Researcher Database

Chikako Nagasato
Field Science Center for Northern Biosphere Aquatic Research Station Muroran Marine Station

Researcher Profile and Settings


  • Field Science Center for Northern Biosphere Aquatic Research Station Muroran Marine Station

Job Title

  • Professor


J-Global ID

Research Interests

  • 受精   中心体   微細構造   褐藻類   受精卵   セントリオール   膜融合   セントリン   細胞骨格   免疫電子顕微鏡   細胞質分裂   電子顕微鏡   オルガネラ   ストラメノパイル   多糖類   多細胞化   不等毛藻類   急速凍結置換法   

Research Areas

  • Life sciences / Morphology, anatomy

Academic & Professional Experience

  • 2020/04 - Today Hokkaido University Field Science Center for Northern Biosphere
  • 2010 Hokkaido University Field Science Center for Northern Biosphere

Association Memberships


Research Activities

Published Papers

  • Lisa Mazéas, Rina Yonamine, Tristan Barbeyron, Bernard Henrissat, Elodie Drula, Nicolas Terrapon, Chikako Nagasato, Cécile Hervé
    Seminars in cell & developmental biology 2022/03/17 
    In brown algae, the extracellular matrix (ECM) and its constitutive polymers play crucial roles in specialized functions, including algal growth and development. In this review we offer an integrative view of ECM construction in brown algae. We briefly report the chemical composition of its main constituents, and how these are interlinked in a structural model. We examine the ECM assembly at the tissue and cell level, with consideration on its structure in vivo and on the putative subcellular sites for the synthesis of its main constituents. We further discuss the biosynthetic pathways of two major polysaccharides, alginates and sulfated fucans, and the progress made beyond the candidate genes with the biochemical validation of encoded proteins. Key enzymes involved in the elongation of the glycan chains are still unknown and predictions have been made at the gene level. Here, we offer a re-examination of some glycosyltransferases and sulfotransferases from published genomes. Overall, our analysis suggests novel investigations to be performed at both the cellular and biochemical levels. First, to depict the location of polysaccharide structures in tissues. Secondly, to identify putative actors in the ECM synthesis to be functionally studied in the future.
  • Chikako Nagasato, Rina Yonamine, Taizo Motomura
    Methods in molecular biology (Clifton, N.J.) 2382 253 - 264 2022 
    Similar to land plant cells, brown algal cells possess plasmodesmata with minute cytoplasmic tunnels, which enable the direct connection between adjacent cells. Plasmodesmata are distributed depending on the association of their formation with cytokinesis. Primary plasmodesmata are formed during cytokinesis, while secondary plasmodesmata appear on the cell wall septum following cytokinesis. Typically, the plasmodesmata of brown algae are cylindrical without the penetration of desmotubules from the endoplasmic reticulum, and there are no morphological differences between primary and secondary plasmodesmata. This present chapter describes the observation of cytokinesis and primary plasmodesmata formation in brown algae using electron microscopy as well as the examination of polysaccharide distribution using antibodies and enzyme-gold probes.
  • Yacine Badis, Delphine Scornet, Minori Harada, Céline Caillard, Olivier Godfroy, Morgane Raphalen, Claire M M Gachon, Susana M Coelho, Taizo Motomura, Chikako Nagasato, J Mark Cock
    The New phytologist 231 (5) 2077 - 2091 2021/09 [Refereed]
    Brown algae are an important group of multicellular eukaryotes, phylogenetically distinct from both the animal and land plant lineages. Ectocarpus has emerged as a model organism to study diverse aspects of brown algal biology, but this system currently lacks an effective reverse genetics methodology to analyse the functions of selected target genes. Here, we report that mutations at specific target sites are generated following the introduction of CRISPR-Cas9 ribonucleoproteins into Ectocarpus cells, using either biolistics or microinjection as the delivery method. Individuals with mutations affecting the ADENINE PHOSPHORIBOSYL TRANSFERASE (APT) gene were isolated following treatment with 2-fluoroadenine, and this selection system was used to isolate individuals in which mutations had been introduced simultaneously at APT and at a second gene. This double mutation approach could potentially be used to isolate mutants affecting any Ectocarpus gene, providing an effective reverse genetics tool for this model organism. The availability of this tool will significantly enhance the utility of Ectocarpus as a model organism for this ecologically and economically important group of marine organisms. Moreover, the methodology described here should be readily transferable to other brown algal species.
  • Rina Yonamine, Kensuke Ichihara, Shiro Tsuyuzaki, Cécile Hervé, Taizo Motomura, Chikako Nagasato
    Journal of phycology 57 (4) 1356 - 1367 2021/08 [Refereed]
    We examined the ultrastructure of the cell wall and immunolocalization of alginates using specific antibodies against M-rich alginates and MG blocks during rhizoid formation in fucoid zygotes, Silvetia babingtonii. The thallus region of 24-h-old zygotes had a cell wall made of three layers with different fiber distribution. In the 12-h-old zygotes, three layers in the thallus were observed before rhizoid formation, namely the inner, middle, and outer layers. During rhizoid elongation, only the inner layer was apparent close to the rhizoid tip area. Immunoelectron microscopy detected M-rich blocks of alginate on the inner half of the cell wall, irrespective of the number of layers in the thallus and rhizoid regions. The MG blocks were seen to cover a slightly wider area than M-rich alginate blocks. It was suggested that parts of M in mannuronan would be rapidly converted to G, and MG-blocks are generated. Transcriptome analysis was performed using 3 -, 10 -, and 24-h-old zygotes after fertilization to examine the relationship between gene expression and alginate synthesis over time. The expression of two mannuronan C5-epimerase homologs that convert mannuronic acid into guluronic acid in alginates was upregulated or downregulated over the course of the examination.
  • Yuan Shen, Taizo Motomura, Chikako Nagasato
    Protoplasma 2021/06/17 [Refereed]
    Mitochondrial morphology varies according to development and the physiological conditions of the cell. Here, we performed electron tomography using serial sections to analyze the number, individual volume, and morphological complexity of mitochondria in the cells across two generations in the life cycle of the brown alga Mutimo cylindricus. This species shows a heteromorphic alternation of generations between the macroscopic gametophyte and the crustose sporophyte during its life cycle and displays anisogamous sexual reproduction. We observed the mitochondria in the vegetative cells of gametophytes and sporophytes to mainly show tubular or discoidal shapes with high morphological complexity. The morphology of the mitochondria in the male and female gametes changed to a nearly spherical or oval shape from a tubular or discoidal shape before release. In this species, degradation of the paternal mitochondria was observed in the zygote 2 h after fertilization. Morphological changes in the mitochondria were not observed until 6 h after fertilization. Twenty-four-hour-old zygotes before and after cytokinesis showed a similar number of mitochondria as 6-h-old zygotes; however, the volume and morphological complexity increased. The results indicated that the maternal mitochondria did not undergo fission or fusion until this stage. Based on the analysis results of the number and total volume of mitochondria before and after the release of the gametes, it is possible that the mitochondria in the female gametes fuse immediately before release.
  • Yuan Shen, Toyoki Iwao, Taizo Motomura, Chikako Nagasato
    Protoplasma 2020/08/29 [Refereed][Not invited]
    Based on the morphology of gametes, sexual reproduction in brown algae is usually classified into three types: isogamy, anisogamy, and oogamy. In isogamy, chloroplasts and chloroplast DNA (chlDNA) in the sporophyte cells are inherited biparentally, while mitochondria (or mitochondrial DNA, mtDNA) is inherited maternally. In oogamy, chloroplasts and mitochondria are inherited maternally. However, the patterns of mitochondrial and chloroplast inheritance in anisogamy have not been clarified. Here, we examined derivation of mtDNA and chlDNA in the zygotes through strain-specific PCR analysis using primers based on single nucleotide polymorphism in the anisogamous brown alga Mutimo cylindricus. In 20-day-old sporophytes after fertilization, mtDNA and chlDNA derived from female gametes were detected, thus confirming the maternal inheritance of both organelles. Additionally, the behavior of mitochondria and chloroplasts in the zygotes was analyzed by examining the consecutive serial sections using transmission electron microscopy. Male mitochondria were isolated or compartmentalized by a double-membrane and then completely digested into a multivesicular structure 2 h after fertilization. Meanwhile, male chloroplasts with eyespots were observed even in 4-day-old, seven-celled sporophytes. The final fate of male chloroplasts could not be traced. Organelle DNA copy number was also examined in female and male gametes. The DNA copy number per chloroplast and mitochondria in male gametes was lower compared with female organelles. The degree of difference is bigger in mtDNA. Thus, changes in different morphology and DNA amount indicate that maternal inheritance of mitochondria and chloroplasts in this species may be based on different processes and timing after fertilization.
  • Ji Won Choi, Louis Graf, Akira F Peters, J Mark Cock, Koki Nishitsuji, Asuka Arimoto, Eiichi Shoguchi, Chikako Nagasato, Chang Geun Choi, Hwan Su Yoon
    Scientific reports 10 (1) 2048 - 2048 2020/02/06 [Refereed][Not invited]
    Among the brown algal lineages, Ectocarpales species have isogamous fertilization in which male and female gametes are morphologically similar. In contrast, female gametes are much larger than male gametes in the oogamous species found in many other brown algal lineages. It has been reported that the plastids of isogamous species are biparentally inherited whereas the plastids of oogamous species are maternally inherited. In contrast, in both isogamous and oogamous species, the mitochondria are usually inherited maternally. To investigate whether there is any relationship between the modes of inheritance and organellar genome architecture, we sequenced six plastid genomes (ptDNA) and two mitochondrial genomes (mtDNA) of isogamous species from the Ectocarpales and compared them with previously sequenced organellar genomes. We found that the biparentally inherited ptDNAs of isogamous species presented distinctive structural rearrangements whereas maternally inherited ptDNAs of oogamous species showed no rearrangements. Our analysis permits the hypothesis that structural rearrangements in ptDNAs may be a consequence of the mode of inheritance.
  • Jie Zhang, Jianting Yao, Zi-Min Hu, Alexander Jueterbock, Norishige Yotsukura, Tatiana N Krupnova, Chikako Nagasato, Delin Duan
    Evolutionary applications 12 (4) 791 - 803 2019/04 
    Studies of postglacial range shifts could enhance our understanding of seaweed species' responses to climate change and hence facilitate the conservation of natural resources. However, the distribution dynamics and phylogeographic diversification of the commercially and ecologically important kelp Saccharina japonica in the Northwest Pacific (NWP) are still poorly surveyed. In this study, we analyzed the evolutionary history of S. japonica using two mitochondrial markers and 24 nuclear microsatellites. A STRUCTURE analysis revealed two partially isolated lineages: lineage H, which is scattered along the coast of Japan; and lineage P, which occurs along the west coast of the Japan Sea. Ecological niche modeling projections to the Last Glacial Maximum (LGM) revealed that the southern coasts of the Japan Sea and the Pacific side of the Oshima and Honshu Peninsulas provided the most suitable habitats for S. japonica, implying that these regions served as ancient refugia during the LGM. Ancient isolation in different refugia may explain the observed divergence between lineages P and H. An approximate Bayesian computation analysis indicated that the two lineages experienced post-LGM range expansion and that postglacial secondary contact occurred in Sakhalin. Model projections into the year 2,100 predicted that S. japonica will shift northwards and lose its genetic diversity center on the Oshima Peninsula in Hokkaido and Shimokita Peninsula in Honshu. The range shifts and evolutionary history of S. japonica improve our understanding of how climate change impacted the distribution range and diversity of this species and provide useful information for the conservation of natural resources under ongoing environmental change in the NWP.
  • Unusual patterns of mitochondrial inheritance in the brown alga Ectocarpus.
    Mignerot, L, Nagasato, C, Peters, A, Perrineau, M. M, Scornet, D, Pontheaux, F, Djema, W, Roze, D, Motomura. T, Coelho, S. M, Cock, J. M
    Molecular Biology and Evolution 2019 [Refereed][Not invited]
  • Quantification of laminarialean zoospores in seawater by real‐time PCR.
    Nagasato, C, Kawamoto, H, Tomioka, T, Tsuyuzaki, S, Kosugi, C, Kato, T, Motomura, T
    Phycological Research 2019 [Refereed][Not invited]
  • The role of egg flagella in the settlement and development of zygotes in two Saccharina species.
    Klochkova, T. A, Motomura, T, Nagasato, C, Klimova, A. V, Kim, G. H
    Phycologia 58 (2) 145 - 153 2019 [Refereed][Not invited]
  • Effect of brefeldin A and the dynamics of the actin plate on cytokinesis of zygotes in the brown alga, Silvetia babingtonii (Fucales, Phaeophyceae).
    Nagasato, C, Motomura, T
    European Journal of Phycology. 54 (1) 26 - 38 2019 [Refereed][Not invited]
  • Olivier Godfroy, Toshiki Uji, Chikako Nagasato, Agnieszka P. Lipinska, Delphine Scornet, Akira F. Peters, Komlan Avia, Sebastien Colin, Laure Mignerot, Taizo Motomura, J. Mark Cock, Susana M. Coelho
    Plant Cell 29 (12) 3102 - 3122 1532-298X 2017/12/01 [Refereed][Not invited]
    Brown algae are one of the most developmentally complex groups within the eukaryotes. As in many land plants and animals, their main body axis is established early in development, when the initial cell gives rise to two daughter cells that have apical and basal identities, equivalent to shoot and root identities in land plants, respectively. We show here that mutations in the Ectocarpus DISTAG (DIS) gene lead to loss of basal structures during both the gametophyte and the sporophyte generations. Several abnormalities were observed in the germinating initial cell in dis mutants, including increased cell size, disorganization of the Golgi apparatus, disruption of the microtubule network, and aberrant positioning of the nucleus. DIS encodes a TBCCd1 protein, which has a role in internal cell organization in animals, Chlamydomonas reinhardtii, and trypanosomes. Our study highlights the key role of subcellular events within the germinating initial cell in the determination of apical/basal cell identities in a brown alga and emphasizes the remarkable functional conservation of TBCCd1 in regulating internal cell organization across extremely distant eukaryotic groups.
  • Nana Kinoshita, Chikako Nagasato, Taizo Motomura
    PHOTOCHEMISTRY AND PHOTOBIOLOGY 93 (5) 1216 - 1223 0031-8655 2017/10 [Refereed][Not invited]
    Brown algal swarmers usually exhibit positive or negative phototaxis. Such behaviors influence the increasing or decreasing dispersal distance or colonization on the new substratum. We confirmed that the sign of phototaxis (negative or positive) in male gametes of Mutimo cylindricus was affected by extracellular Ca2+ influx through Ca2+ channels. Under the control condition (10(-2) m [Ca2+]), male gametes swimming with a helical rotation of their cell body mostly showed positive phototaxis. At 10(-3) m [Ca2+], more than half of the male gametes showed positive phototaxis, whereas the others showed negative phototaxis. From 10(-4)-10(-5) m [Ca2+], the phototactic sign changed to negative. When these negative phototactic gametes were transferred back to the control condition, the phototactic sign reverted to positive. At 10(-6) m [Ca2+], some of male gametes showed negative phototaxis, but most showed no phototaxis or flagellar beating. Lanthanum, a Ca2+ channel blocker, affected the sign of phototaxis at 10(-4) m [La3+] under 10(-2) m [Ca2+], and male gametes mostly showed negative phototaxis. A further increase in [La3+] inhibited phototaxis and flagellar beating. These results pointed out the involvement of Ca2+ channels that were blocked by La3+ in phototaxis and flagellar beating.
  • Atsuko Tanaka, Yoichiro Hoshino, Chikako Nagasato, Taizo Motomura
    PROTOPLASMA 254 (3) 1341 - 1351 0033-183X 2017/05 [Refereed][Not invited]
    Tissue wounds are mainly caused by herbivory, which is a serious threat for macro-algae, and brown algae are known to regenerate branches or buds in response to wounding. In the present paper, we describe a branch regeneration system, induced by sever damage, in the brown alga Dictyota dichotoma. Segmentations of juvenile thalli induced branch regenerations unless explants possessed apical cells. Apical excisions in distinct positions elucidated that disruption of an apical cell or disconnection of tissue with an apical cell triggered the branch regeneration. Furthermore, spatial positions of regenerated branches seemed to be regulated by the apical region, which was assumed to generate inhibitory effects for lateral branch regeneration. Mechanical incision, which disrupted tissue continuity with the apical region, induced branch regeneration preferentially below the incision. Although we were unable to identify the candidate inhibitory substance, our results suggested that the apical region may have an inhibitory effect on lateral branch regeneration. Additionally, observations of branch regeneration showed that all epidermal cells in D. dichotoma possess the ability to differentiate into apical cells, directly. This may be the first report of algal transdifferentiation during the wound-stress response.
  • Nana Kinoshita, Chikako Nagasato, Taizo Motomura
    JOURNAL OF PLANT RESEARCH 130 (3) 443 - 453 0918-9440 2017/05 [Refereed][Not invited]
    Brown algae exhibit three patterns of sexual reproduction: isogamy, anisogamy, and oogamy. Unicellular swarmers including gametes and zoospores bear two heterogenous flagella, an anterior flagellum with mastigonemes (fine tripartite hairs) and a posterior one. In seawater, these flagellates usually receive physico-chemical signals for finding partners and good habitats. It is well known that brown algal swarmers change their swimming direction depending on blue light (phototaxis), and male gametes do so, based on the sex pheromones from female gametes (chemotaxis). In recent years, the comparative analysis of chemotaxis in isogamy, anisogamy, and oogamy has been conducted. In this paper, we focused on the phototaxis and chemotaxis of brown algal gametes comparing the current knowledge with our recent studies.
  • Chikako Nagasato, Atsuko Tanaka, Toshiaki Ito, Christos Katsaros, Taizo Motomura
    JOURNAL OF PHYCOLOGY 53 (2) 333 - 341 0022-3646 2017/04 [Refereed][Not invited]
    Despite the high number of studies on the fine structure of brown algal cells, only limited information is available on the intercelluar transportation of molecules via plasmodesmata in brown algae. In this study, plasmodesmatal permeability of Halopteris congesta was examined by observing the translocation of microinjected fluorescent tracers of different molecular sizes. The tip region of H. congesta consists of a cylindrical apical cell, while the basal region is multiseriate. Fluorescein isothiocyanate-dextran (FD; 3, 10, and 20 kDa) and recombinant green fluorescent protein (27 kDa) were injected into the apical cell and were observed to diffuse into the neighboring cells. FD of 40 kDa was detected only in the injected apical cell. The plasmodesmatal size exclusion limit was considered to be more than 20 kDa and less than 40 kDa. The extent of translocation of 3 and 10 kDa FD from the apical to neighboring cells 2 h postinjection was estimated based on the fluorescence intensity. It was suggested that the diffusing capacity of plasmodesmata varied according to molecular size. In order to examine acropetal and/or basipetal direction of molecular movement, 3 and 10 kDa FD were injected into the third cell from the apical cell. Successive observations indicated that the diffusion of fluorescence in the acropetal direction took longer than that in the basipetal direction. No ultrastructural difference in plasmodesmata was noted among the cross walls.
  • Nana Kinoshita, Chikako Nagasato, Taizo Motomura
    PROTOPLASMA 254 (1) 547 - 555 0033-183X 2017/01 [Refereed][Not invited]
    In oogamous species of brown algae such as Saccharina japonica and Fucus distichus, the sperm possess an unusual long posterior flagellum, which oscillates actively and produces a propulsive force during swimming. In this study, we quantitatively analyzed the effect of chemotactic responses on sperm swimming and flagellar waveforms by high-speed video recordings. We found that the thigmotactic response to the chemo-attractant was not enhanced during chemotactic swimming and that the swimming velocity of sperm did not decrease. As concentration of the chemo-attractant decreased, the sperm performed drastic U-turn movements, which was caused by a rapid and large bend of the posterior flagellum. Unilateral bending of the posterior flagellum when sensing a decrease in the concentration of the chemo-attractant may be a common response in male gametes during fertilization of brown algae both oogamous and isogamous species.
  • Kazumasa Yamada, Chikako Nagasato, Taizo Motomura, Mutsuo Ichinomiya, Akira Kuwata, Mitsunobu Kamiya, Kaori Ohki, Shinya Yoshikawa
    PROTOPLASMA 254 (1) 461 - 471 0033-183X 2017/01 [Refereed][Not invited]
    The parmalean algae possess a siliceous wall and represent the sister lineage of diatoms; they are thought to be a key group for understanding the evolution of diatoms. Diatoms possess well-characterized and unique mitotic structures, but the mitotic apparatus of Parmales is still unknown. We observed the microtubule (MT) array during interphase and mitosis in Triparma laevis using TEM. The interphase cells had four or five centrioles (similar to 80 nm in length), from which MTs emanated toward the cytoplasm. In prophase, the bundle of MTs arose at an extranuclear site. The position of centrioles with respect to an MT bundle changed during its elongation. Centrioles were observed on the lateral side of a shorter MT bundle (similar to 590 nm) and on either side of an extended MT bundle (similar to 700 nm). In metaphase, the spindle consisted of two types of MTs-MT bundle that passed through a cytoplasmic tunnel in the center of the nucleus and single MTs (possibly kinetochore MTs) that extended from the poles into the nucleus. The nuclear envelope disappeared only at the regions where the kinetochore MTs penetrated. In telophase, daughter chromosomes migrated toward opposite poles, and the MT bundle was observed between segregating chromosomes. These observations showed that MT nucleation does not always occur at the periphery of centrioles through cell cycle and that the spindle of T. laevis has a similar configuration to that of diatoms.
  • Makoto Terauchi, Chikako Nagasato, Akira Inoue, Toshiaki Ito, Taizo Motomura
    PLANTA 244 (2) 361 - 377 0032-0935 2016/08 [Refereed][Not invited]
    This work investigated a correlation between the three-dimensional architecture and compound-components of the brown algal cell wall. Calcium greatly contributes to the cell wall integrity. Brown algae have a unique cell wall consisting of alginate, cellulose, and sulfated polysaccharides. However, the relationship between the architecture and the composition of the cell wall is poorly understood. Here, we investigated the architecture of the cell wall and the effect of extracellular calcium in the sporophyte and gametophyte of the model brown alga, Ectocarpus siliculosus (Dillwyn) Lyngbye, using transmission electron microscopy, histochemical, and immunohistochemical studies. The lateral cell wall of vegetative cells of the sporophyte thalli had multilayered architecture containing electron-dense and negatively stained fibrils. Electron tomographic analysis showed that the amount of the electron-dense fibrils and the junctions was different between inner and outer layers, and between the perpendicular and tangential directions of the cell wall. By immersing the gametophyte thalli in the low-calcium (one-eighth of the normal concentration) artificial seawater medium, the fibrous layers of the lateral cell wall of vegetative cells became swollen. Destruction of cell wall integrity was also induced by the addition of sorbitol. The results demonstrated that electron-dense fibrils were composed of alginate-calcium fibrous gels, and electron negatively stained fibrils were crystalline cellulose microfibrils. It was concluded that the spatial arrangement of electron-dense fibrils was different between the layers and between the directions of the cell wall, and calcium was necessary for maintaining the fibrous layers in the cell wall. This study provides insights into the design principle of the brown algal cell wall.
  • Sae Kikutani, Kensuke Nakajima, Chikako Nagasato, Yoshinori Tsuji, Ai Miyatake, Yusuke Matsuda
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 113 (35) 9828 - 9833 0027-8424 2016/08 [Refereed][Not invited]
    The algal pyrenoid is a large plastid body, where the majority of the CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) resides, and it is proposed to be the hub of the algal CO2-concentrating mechanism(CCM) and CO2 fixation. The thylakoid membrane is often in close proximity to or penetrates the pyrenoid itself, implying there is a functional cooperation between the pyrenoid and thylakoid. Here, GFP tagging and immunolocalization analyses revealed that a previously unidentified protein, Pt43233, is targeted to the lumen of the pyrenoid-penetrating thylakoid in the marine diatom Phaeodactylum tricornutum. The recombinant Pt43233 produced in Escherichia coli cells had both carbonic anhydrase (CA) and esterase activities. Furthermore, a Pt43233:GFP-fusion protein immunoprecipitated from P. tricornutum cells displayed a greater specific CA activity than detected for the purified recombinant protein. In an RNAi-generated Pt43233 knockdown mutant grown in atmospheric CO2 levels, photosynthetic dissolved inorganic carbon (DIC) affinity was decreased and growth was constantly retarded; in contrast, overexpression of Pt43233: GFP yielded a slightly greater photosynthetic DIC affinity. The discovery of a theta-type CA localized to the thylakoid lumen, with an essential role in photosynthetic efficiency and growth, strongly suggests the existence of a common role for the thylakoid-luminal CA with respect to the function of diverse algal pyrenoids.
  • Nana Kinoshita, Kogiku Shiba, Kazuo Inaba, Gang Fu, Chikako Nagasato, Taizo Motomura
    EUROPEAN JOURNAL OF PHYCOLOGY 51 (2) 139 - 148 0967-0262 2016/05 [Refereed][Not invited]
    Brown algae are members of the Stramenopiles and their gametes generally have two heterogeneous flagella: a long anterior flagellum (AF) with mastigonemes and a short posterior flagellum (PF). In this study, swimming paths and flagellar waveforms in free-swimming and thigmotactic-swimming male and female gametes and in male gametes during chemotaxis, were quantitatively analysed in the model brown alga Ectocarpus siliculosus. This analysis was performed using a high-speed video camera. It was revealed that the AF plays a role in changing the locomotion of male and female gametes from free-swimming to thigmotactic-swimming and also in changing the swimming path of male gametes from linear to circular during chemotaxis. In the presence of a sex pheromone, male gametes changed their swimming path from linear (swimming path curvature, 0-0.02 mu m(-1)) to middle and small circular path (swimming path curvature, 0.04-0.20 mu m(-1)). The flagellar asymmetry and the deflection angle of the AF became larger, whereas the oscillation pattern of the AF was stable. However, there was no correlation between the flagellar asymmetry and the deflection angle of the AF and the path curvature when the male gametes showed middle to small circular paths. The PF irregularly changed the deflection angle and the oscillation pattern was unstable depending on the gradient of the sex pheromone concentration. AF waveforms were independent of PF locomotion during chemotaxis. This means that the AF has the ability to change the swimming path of male gametes - for example, from a highly linear path to a circular path - while changes in locomotion from a middle circle path to a small circle path is the result of beating of the PF.
  • Gang Fu, Chikako Nagasato, Takahiro Yamagishi, Hiroshi Kawai, Kazuo Okuda, Yoshitake Takao, Takeo Horiguchi, Taizo Motomura
    PROTOPLASMA 253 (3) 929 - 941 0033-183X 2016/05 [Refereed][Not invited]
    Most swarmers (swimming cells) of the stramenopile group, ranging from unicellular protist to giant kelps (brown algae), have two heterogeneous flagella: a long anterior flagellum (AF) and a relatively shorter posterior flagellum (PF). These flagellated cells often exhibit phototaxis upon light stimulation, although the mechanism by which how the phototactic response is regulated remains largely unknown. A flavoprotein concentrating at the paraflagellar body (PFB) on the basal part of the PF, which can emit green autofluorescence under blue light irradiance, has been proposed as a possible blue light photoreceptor for brown algal phototaxis although the nature of the flavoprotein still remains elusive. Recently, we identified helmchrome as a PF-specific flavoprotein protein in a LC-MS/MS-based proteomics study of brown algal flagella (Fu et al. 2014). To verify the conservation of helmchrome, in the present study, the absence or presence and the localization of helmchrome in swarmers of various algal species were investigated. The results showed that helmchrome was only detected in phototactic swarmers but not the non-phototactic ones of the stramenopile group. Electron microscopy further revealed that the helmchrome detectable swarmers bear a conserved PFB-eyespot complex, which may serve as structural basis for light sensing. It is speculated that all three conserved properties: helmchrome, the PFB structure, and the eyespot apparatus, will be essential parts for phototaxis of stramenopile swarmers.
  • Formation of primary intercellular connections in multicellular algae. (in Japanese)
    Nagasato, C, Terauchi, M, Motomura, T
    Microscopy 51 140 - 144 2016 [Refereed][Not invited]
  • Nana Kinoshita, Chikako Nagasato, Atsuko Tanaka, Taizo Motomura
    PHYCOLOGIA 55 (4) 359 - 364 0031-8884 2016 [Refereed][Not invited]
    Locomotion of female and male gametes of Mutimo cylindricus was analysed using a high-speed recording system. Female and male gametes morphologically differed in terms of their cell size and flagellar length. Male gametes swam significantly faster than female gametes; although, the flagellar waveforms were almost the same. Thus, the different swimming velocities of male and female gametes may have been due to differences in their cell size. Chemotactic male gametes treated with the sex pheromone from settled female gametes behaved in a similar manner to the male gametes of the isogamous Ectocarpus siliculosus. The results of the study revealed the following: (1) free-swimming male gametes exhibited thigmotaxis, (2) the beat frequency of the anterior flagellum and the swimming velocity decreased, (3) the deflection angle of the anterior flagellum increased, (4) the unilateral beat of the posterior flagellum was affected by the sex pheromone gradient, and (5) the tracking radius of male gametes around female gametes decreased.
  • Kazumasa Yamada, Shinya Yoshikawa, Kaori Ohki, Mutsuo Ichinomiya, Akira Kuwata, Taizo Motomura, Chikako Nagasato
    PHYCOLOGIA 55 (5) 602 - 609 0031-8884 2016 [Refereed][Not invited]
    The marine alga Triparma laevis NIES-2565, belonging to the Parmales (Bolidophyceae), possesses a siliceous cell wall that is composed of shield, ventral, dorsal and girdle plates. The cell wall is lost under silicate-deficient culture conditions. Regeneration of the cell wall occurs with the addition of sufficient silicate ions into the culture medium. In this study, the formation of the siliceous cell wall was observed by transmission electron microscopy. Silica deposition vesicles (SDVs) forming the shield and ventral plates were initially found around the chloroplast, moving toward the plasma membrane as they expanded, with siliceous plates being built within the SDV. The SDV membrane was tightly adpressed to the siliceous plate. In contrast, SDVs for dorsal and girdle plates were formed adjacent to the plasma membrane. Extracellular secretion of mature siliceous plates began with shield plates, followed in turn by ventral, dorsal and girdle plates. The dorsal and girdle plates were inserted into the space between the previously secreted shield and ventral plates. Our study demonstrates that SDVs develop in different areas of the cell, according to whether they are forming dorsal and girdle plates or shield and ventral plates.
  • Jie Zhang, Jian-Ting Yao, Zhong-Min Sun, Gang Fu, Dmitry A. Galanin, Chikako Nagasato, Taizo Motomura, Zi-Min Hu, De-Lin Duan
    BMC EVOLUTIONARY BIOLOGY 15 1471-2148 2015/11 [Refereed][Not invited]
    Background: Population structure and genetic diversity of marine organisms in the Northwestern Pacific Ocean exhibited complex patterns. Saccharina japonica is a commercially and ecologically important kelp species widely distributed along the coast of Japan Sea. However, it is still poorly known about population genetics and phylogeographic patterns of wild S. japonica populations on a large geographic scale, which is an important contribution to breeding and conservation of this marine crop. Results: We collected 612 mitochondrial COI and trnW-trnL sequences. Diversity indices suggested that S. japonica populations along the coast of Hokkaido exhibited the highest genetic diversity. Bayesian Analysis of Population Structure (BAPS) revealed four clusters in the kelp species (cluster 1: Hokkaido and South Korea; cluster 2: northwestern Hokkaido; cluster 3: Far Eastern Russia; cluster 4: China). The network inferred from concatenated data exhibited two shallow genealogies corresponding to two BAPS groups (cluster 2 and cluster 3). We did not detect gene flow between the two shallow genealogies, but populations within genealogy have asymmetric gene exchange. Bayesian skyline plots and neutrality tests suggested that S. japonica experienced postglacial expansion around 10.45 ka. Conclusions: The coast of Hokkaido might be the origin and diversification center of S. japonica. Gene exchange among S. japonica populations could be caused by anthropogenic interference and oceanographic regimes. Postglacial expansions and gene exchange apparently led to more shared haplotypes and less differentiation that in turn led to the present shallow phylogeographical patterns in S. japonica.
  • Chikako Nagasato, Makoto Terauchi, Atsuko Tanaka, Taizo Motomura
    BOTANICA MARINA 58 (3) 229 - 238 0006-8055 2015/06 [Refereed][Not invited]
    Brown algae have plasmodesmata, tiny tubular cytoplasmic channels connecting adjacent cells. The lumen of plasmodesmata is 10-20 nm wide, and it takes a simple form, without a desmotubule (the inner membrane structure consisting of endoplasmic reticulum in the plasmodesmata of green plants). In this study, we analyzed the ultrastructure and distribution of plasmodesmata during development of Fucus distichus zygotes. The first cytokinesis of zygotes in brown algae is not accompanied by plasmodesmata formation. As the germlings develop, plasmodesmata are found in all septal cell walls, including the first cell division plane. Plasmodesmata are formed de novo on the existing cell wall. Pit fields, which are clusters of plasmodesmata, were observed in germlings with differentiated cell layers. Apart from the normal plasmodesmata, these pit fields had branched plasmodesmata that appeared to arise from the lateral preexisting ones. Fluorescent tracers with different molecular sizes were microinjected to examine the size exclusion limit of molecules for transit through the plasmodesmata. Fluorescein isothiocyanate (FITC)-dextran of 3 kDa size was spread over the germlings, and 10 kDa FITC-dextran was tracked only in the rhizoid. The size exclusion limit was <10 kDa for the thallus but <40 kDa for the rhizoid.
  • Masahiko Idei, Shinya Sato, Chikako Nagasato, Taizo Motomura, Kensuke Toyoda, Tamotsu Nagumo, David G. Mann
    JOURNAL OF PHYCOLOGY 51 (1) 144 - 158 0022-3646 2015/02 [Refereed][Not invited]
    Spermatogenesis and auxospore development were studied in the freshwater centric diatom Hydrosera triquetra. Spermatogenesis was unusual, lacking depauperating cell divisions within the spermatogonangium. Instead, a series of mitoses occurred within an undivided cell to produce a multinucleate plasmodium with peripheral nuclei, which then underwent meiosis. 32 or 64 sperm budded off from the plasmodium leaving a large residual cell containing all the chloroplasts. Similar development apparently occurs in Pleurosira, Aulacodiscus, and Guinardia, these being so distantly related that independent evolution of plasmodial spermatogenesis seems likely. After presumed fertilization, the Hydrosera egg cell expanded distally to form a triangular end part. However, unlike in other triangular diatoms (Lithodesmium, Triceratium), the development of triradiate symmetry was not controlled by the "canonical" method of a perizonium that constrains expansion to small terminal areas of the auxospore wall. Instead, the auxospore wall lacked a perizonium and possessed only scales and a dense mat of thin, apparently entangled strips of imperforate silica. No such structures have been reported from any other centric diatoms, the closest analogs being instead the incunabular strips of some raphid diatoms (Nitzschia and Pinnularia). Whether these silica structures are formed by the normal method (intracellular deposition within a silica deposition vesicle) is unknown. As well as being more rounded than vegetative cells, the initial cell is aberrant in its structure, since it has a less polarized distribution of the "triptych" pores characteristic of the species.
  • Kazumasa Yamada, Chikako Nagasato, Taizo Motomura, Mutsuo Ichinomiya, Akira Kuwata, Mitsunobu Kamiya, Kaori Ohki, Shinya Yoshikawa
    EUROPEAN JOURNAL OF PHYCOLOGY 50 155 - 156 0967-0262 2015 [Refereed][Not invited]
  • Makoto Terauchi, Chikako Nagasato, Taizo Motomura
    JOURNAL OF PLANT RESEARCH 128 (1) 7 - 15 0918-9440 2015/01 [Refereed][Not invited]
    Plasmodesmata (PD) are intercellular connections in plants which play roles in various developmental processes. They are also found in brown algae, a group of eukaryotes possessing complex multicellularity, as well as green plants. Recently, we conducted an ultrastructural study of PD in several species of brown algae. PD in brown algae are commonly straight plasma membrane-lined channels with a diameter of 10-20 nm and they lack desmotubule in contrast to green plants. Moreover, branched PD could not be observed in brown algae. In the brown alga, Dictyota dichotoma, PD are produced during cytokinesis through the formation of their precursor structures (pre-plasmodesmata, PPD). Clustering of PD in a structure termed "pit field" was recognized in several species having a complex multicellular thallus structure but not in those having uniseriate filamentous or multiseriate one. The pit fields might control cell-to-cell communication and contribute to the establishment of the complex multicellular thallus. In this review, we discuss fundamental morphological aspects of brown algal PD and present questions that remain open.
  • Jong Won Han, Tatyana A. Klochkova, Junbo Shim, Chikako Nagasato, Taizo Motomura, Gwang Hoon Kim
    PLANTA 240 (6) 1253 - 1267 0032-0935 2014/12 [Refereed][Not invited]
    Metabolic pathways of cell organelles may influence the expression of nuclear genes involved in fertilization and subsequent zygote development through a retrograde regulation. In Scytosiphon lomentaria, inheritance of chloroplast is biparental but mitochondria are maternally inherited. Male and female gametes underwent different parthenogenetic outcomes. Most (> 99 %) male gametes did not differentiate rhizoid cells or survived beyond four-cell stage, while over 95 % of female gametes grew into mature asexual plants. Proteomic analysis showed that the protein contents of male and female gametes differed by approximately 1.7 %, 12 sex-specific proteins out of 700 detected proteins. Three sex-specific proteins were isolated and identified using CAF-MALDI mass spectrometry and RACE-PCR. Among them, a male gamete-specific homoaconitate hydratase (HACN) and a female gamete-specific succinate semialdehyde dehydrogenase (SSADH) were predicted to be the genes involved in mitochondrial metabolic pathways. The expression level of both mitochondrial genes was dramatically changed at the fertilization event. During parthenogenetic development the male-specific HACN and GTP-binding protein were gradually down-regulated but SSADH stayed up-regulated up to 48 h. To observe the effect of chemicals on the expression of these genes, male and female gametes were treated with gamma-aminobutyric acid (GABA), hydrogen peroxide and l-ascorbic acid. Among them GABA treatment significantly reduced SSADH gene expression in female gamete but the same treatment induced high upregulation of the gene in male gamete. GABA treatment affected the behavior of gametes and their parthenogenetic development. Both gametes showed prolonged motile stage, retarded settlement and subsequent parthenogenetic development. Our results suggest that male and female gametes regulate mitochondrial metabolic pathways differentially during fertilization, which may be the reason for their physiological and behavioral differences.
  • Chikako Nagasato, Naoko Kajimura, Makoto Terauchi, Yoshinobu Mineyuki, Taizo Motomura
    PROTOPLASMA 251 (6) 1347 - 1357 0033-183X 2014/11 [Refereed][Not invited]
    In brown algae, membrane resources for the new cell partition during cytokinesis are mainly flat cisternae (FCs) and Golgi-derived vesicles. We used electron tomography coupled with rapid freezing/freeze substitution of zygotes to clarify the structure of transient membrane compartments during cytokinesis in Silvetia zygotes. After mitosis, an amorphous membranous structure, considered to be an FC intermediate was observed near endoplasmic reticulum clusters, lying between two daughter nuclei. FCs were arrayed at the cytokinetic plane, and a tubular membranous network was formed around them. This network might be formed by the consecutive fusion of spherical vesicles that are linked to the edges of FCs to form a membranous network (MN). At the initial stage of the formation of a membranous sac (MS) from the MN, the MS had flat and swollen parts, with the latter showing membranous tunnels. Coated pits were detected with high frequency at the swollen parts of the MS. This observation indicated that membranous tunnels disappeared by recycling of excess membrane via endocytosis, and the swollen part became flat. The MN appeared at the edges of the growing MS. MN and the MN-MS complex were observed along the cytokinetic plane in several spaces. The MS expanded by the incorporation of MN or other MS in its neighborhood. With the maturation of the new cell partition membrane, the thickness of the MS became constant and the membrane cavity disappeared. The changes in the surface area and volume of the transient membrane compartment during cytokinesis were analyzed from the tomographic data.
  • Gang Fu, Chikako Nagasato, Seiko Oka, J. Mark Cock, Taizo Motomura
    PROTIST 165 (5) 662 - 675 1434-4610 2014/09 [Refereed][Not invited]
    Flagella are conserved organelles among eukaryotes and they are composed of many proteins, which are necessary for flagellar assembly, maintenance and function. Stramenopiles, which include brown algae, diatoms and oomycetes, possess two laterally inserted flagella. The anterior flagellum (AF) extends forward and bears tripartite mastigonemes, whilst the smooth posterior flagellum (PF) often has a paraflagellar body structure. These heterogeneous flagella have served as crucial structures in algal studies especially from a viewpoint of phylogeny. However, the protein compositions of the flagella are still largely unknown. Here we report a LC-MS/MS based proteomics analysis of brown algal flagella. In total, 495 flagellar proteins were identified. Functional annotation of the proteome data revealed that brown algal flagellar proteins were associated with cell motility, signal transduction and various metabolic activities. We separately isolated AF and PF and analyzed their protein compositions. This analysis led to the identification of several AF- and PF-specific proteins. Among the PF-specific proteins, we found a candidate novel blue light receptor protein involved in phototaxis, and named it HELMCHROME because of the steering function of PF. Immunological analysis revealed that this protein was localized along the whole length of the PF and concentrated in the paraflagellar body. (C) 2014 Elsevier GmbH. All rights reserved.
  • Tomonori Sato, Chikako Nagasato, Yoshiaki Hara, Taizo Motomura
    PROTIST 165 (2) 113 - 122 1434-4610 2014/03 [Refereed][Not invited]
    The cells of cryptophycean and chlorarachniophycean algae contain a nucleomorph, a vestigial nucleus derived from red and green algal endosymbionts respectively. The origin of the nucleomorph is therefore different from that of cellular organelles such as mitochondria and chloroplasts. In this study, we sought to determine whether cell cycle regulation of the nucleomorph in the cryptophycean alga Pyrenomonas helgolandii is functionally similar to that of the cell nucleus. We performed an ultrastructural analysis of nucleomorph division in cells prepared by rapid freezing fixation - freeze substitution and also carried out BrdU labeling experiments to determine the timing of nucleomorph DNA synthesis in relation to that of the cell nucleus. In cells cultured under 16 hours light: 8 hours dark conditions, BrdU labeling experiments showed that DNA synthesis in the nucleomorph occurred during a limited period from 2 hr to 4 hr after the beginning of the dark period. The S phase in the nucleomorph started just after completion of the nuclear S phase. Thus, DNA synthesis in the nucleomorph occurred at a defined period of the cell cycle. By contrast, our BrdU experiments showed that the nucleoids of mitochondria and chloroplasts could perform DNA synthesis throughout the whole cell cycle. (C) 2014 Elsevier GmbH. All rights reserved.
  • Tatyana A. Klochkova, Min Seok Kwak, Jong Won Han, Taizo Motomura, Chikako Nagasato, Gwang Hoon Kim
    ALGAE 28 (2) 185 - 192 1226-2617 2013/06 [Refereed][Not invited]
    A new cold-adapted Arctic strain of Haematococcus pluvialis from Blomstrandhalvoya Island (Svalbard) is described. This strain is predominantly always in non-motile palmelloid stage. Transmission electron microscopy showed the presence of very thick cell wall and abundant lipid vesicles in the palmelloids, including red and green cells. The external morphology of the non-motile palmelloid and motile bi-flagellated cells of our strain is similar to H. pluvialis; however it differs from H. pluvialis in physiology. Our strain is adapted to live and produce astaxanthin in the low temperature (4-10 degrees C), whilst the usual growth temperature for H. pluvialis is between 20-27 degrees C. Phylogenetic analysis based on 18S rRNA gene data showed that our strain nested within the Haematococcus group, forming a sister relationship to H. lacustris and H. pluvialis, which are considered synonymous. Therefore, we identified our Arctic strain as H. pluvialis.
  • Gang Fu, Chikako Nagasato, Toshiaki Ito, Dieter G. Müller, Taizo Motomura
    Protoplasma 250 (1) 261 - 272 0033-183X 2013 [Refereed][Not invited]
    Flagellar development in the plurilocular zoidangia of sporophytes of the brown alga Ectocarpus siliculosus was analyzed in detail using transmission electron microscopy and electron tomography. A series of cell divisions in the plurilocular zoidangia produced the spore-mother cells. In these cells, the centrioles differentiated into flagellar basal bodies with basal plates at their distal ends and attached to the plasma membrane. The plasma membrane formed a depression (flagellar pocket) into where the flagella elongated and in which variously sized vesicles and cytoplasmic fragments accumulated. The anterior and posterior flagella started elongating simultaneously, and the vesicles and cytoplasmic fragments in the flagellar pocket fused to the flagellar membranes. The two flagella (anterior and posterior) could be clearly distinguished from each other at the initial stage of their development by differences in length, diameter and the appendage flagellar rootlets. Flagella continued to elongate in the flagellar pocket and maintained their mutually parallel arrangement as the flagellar pocket gradually changed position. In mature zoids, the basal part of the posterior flagellum (paraflagellar body) characteristically became swollen and faced the eyespot region. Electron dense materials accumulated between the axoneme and the flagellar membrane, and crystallized materials could also be observed in the swollen region. Before liberation of the zoospores from the plurilocular zoidangia, mastigoneme attachment was restricted to the distal region of the anterior flagellum. Structures just below the flagellar membrane that connected to the mastigonemes were clearly visible by electron tomography. © 2012 Springer-Verlag.
  • Makoto Terauchi, Chikako Nagasato, Naoko Kajimura, Yoshinobu Mineyuki, Kazuo Okuda, Christos Katsaros, Taizo Motomura
    PLANTA 236 (4) 1013 - 1026 0032-0935 2012/10 [Refereed][Not invited]
    Plasmodesmata are intercellular bridges that directly connect the cytoplasm of neighboring cells and play a crucial role in cell-to-cell communication and cell development in multicellular plants. Although brown algae (Phaeophyceae, Heterokontophyta) are phylogenetically distant to land plants, they nevertheless possess a complex multicellular organization that includes plasmodesmata. In this study, the ultrastructure and formation of plasmodesmata in the brown alga Dictyota dichotoma were studied using transmission electron microscopy and electron tomography with rapid freezing and freeze substitution. D. dichotoma possesses plasma membrane-lined, simple plasmodesmata without internal endoplasmic reticulum (desmotubule). This structure differs from those in land plants. Plasmodesmata were clustered in regions with thin cell walls and formed pit fields. Fine proteinaceous "internal bridges" were observed in the cavity. Ultrastructural observations of cytokinesis in D. dichotoma showed that plasmodesmata formation began at an early stage of cell division with the formation of tubular pre-plasmodesmata within membranous sacs of the cytokinetic diaphragm. Clusters of pre-plasmodesmata formed the future pit field. As cytokinesis proceeded, electron-dense material extended from the outer surface of the mid region of the pre-plasmodesmata and finally formed the nascent cell wall. From these results, we suggest that pre-plasmodesmata are associated with cell wall development during cytokinesis in D. dichotoma.
  • J. Mark Cock, Lieven Sterck, Sophia Ahmed, Andrew E. Allen, Grigoris Amoutzias, Veronique Anthouard, François Artiguenave, Alok Arun, Jean-Marc Aury, Jonathan H. Badger, Bank Beszteri, Kenny Billiau, Eric Bonnet, John H. Bothwell, Chris Bowler, Catherine Boyen, Colin Brownlee, Carl J. Carrano, Bénédicte Charrier, Ga Youn Cho, Susana M. Coelho, Jonas Collén, Gildas Le Corguillé, Erwan Corre, Laurence Dartevelle, Corinne Da Silva, Ludovic Delage, Nicolas Delaroque, Simon M. Dittami, Sylvie Doulbeau, Marek Elias, Garry Farnham, Claire M.M. Gachon, Olivier Godfroy, Bernhard Gschloessl, Svenja Heesch, Kamel Jabbari, Claire Jubin, Hiroshi Kawai, Kei Kimura, Bernard Kloareg, Frithjof C. Küpper, Daniel Lang, Aude Le Bail, Rémy Luthringer, Catherine Leblanc, Patrice Lerouge, Martin Lohr, Pascal J. Lopez, Nicolas Macaisne, Cindy Martens, Florian Maumus, Gurvan Michel, Diego Miranda-Saavedra, Julia Morales, Hervé Moreau, Taizo Motomura, Chikako Nagasato, Carolyn A. Napoli, David R. Nelson, Pi Nyvall-Collén, Akira F. Peters, Cyril Pommier, Philippe Potin, Julie Poulain, Hadi Quesneville, Betsy Read, Stefan A. Rensing, Andrés Ritter, Sylvie Rousvoal, Manoj Samanta, Gaelle Samson, Declan C. Schroeder, Delphine Scornet, Béatrice Ségurens, Martina Strittmatter, Thierry Tonon, James W. Tregear, Klaus Valentin, Peter Von Dassow, Takahiro Yamagishi, Pierre Rouzé, Yves Van de Peer, Patrick Wincker
    Advances in Botanical Research 64 141 - 184 0065-2296 2012 [Not refereed][Not invited]
    Brown algae are important organisms both because of their key ecological roles in coastal ecosystems and because of the remarkable biological features that they have acquired during their unusual evolutionary history. The recent sequencing of the complete genome of the filamentous brown alga Ectocarpus has provided unprecedented access to the molecular processes that underlie brown algal biology. Analysis of the genome sequence, which exhibits several unusual structural features, identified genes that are predicted to play key roles in several aspects of brown algal metabolism, in the construction of the multicellular bodyplan and in resistance to biotic and abiotic stresses. Information from the genome sequence is currently being used in combination with other genomic, genetic and biochemical tools to further investigate these and other aspects of brown algal biology at the molecular level. Here, we review some of the major discoveries that emerged from the analysis of the Ectocarpus genome sequence, with a particular focus on the unusual genome structure, inferences about brown algal evolution and novel aspects of brown algal metabolism. © 2012 Elsevier Ltd.
  • Christos I. Katsaros, Vasilios Varvarigos, Claire M. M. Gachon, Jerry Brand, Taizo Motomura, Chikako Nagasato, Frithjof C. Kuepper
    PROTIST 162 (2) 315 - 331 1434-4610 2011/04 [Refereed][Not invited]
    A detailed comparative examination of microtubule (MT) organization in interphase and dividing cells of Uronema sp., Klebsormidium flaccidum, K. subtilissimum, Stichococcus bacillaris and S. chloranthus was made using tubulin immunofluorescence and transmission electron microscopy (TEM). During interphase all the species bear a well-organized cortical MT system, consisting of parallel bundles with different orientations. In Uronema sp. the cortical MT bundles are longitudinally oriented, whereas in the other species they are in transverse orientation to the axis of the cells. Considerable differences in MT organization were also observed during stages of mitosis, mainly preprophase, as well as cytokinesis. In Uronema sp., a particular radial MT assembly is organized during preprophase-early prophase, which was not observed in the other species. In Stichococcus a fine MT ring surrounded the nucleus during preprophase and prophase. An MT ring, together with single cytoplasmic MTs, was also found associated with the developing diaphragm during cytokinesis in Stichococcus. A phycoplast participates in cytokinesis in Uronema sp., but not in the other species. In Uronema sp. the centrosome functions as a microtubule organizing center (MTOC) during mitosis, but not during interphase and cytokinesis. The phylogenetic significance of these differences is discussed in combination with SSU/ITS sequencing and other, existing molecular data. (C) 2010 Elsevier GmbH. All rights reserved.
  • Kei Kimura, Chikako Nagasato, Shinya Uwai, Taizo Motomura
    CYTOLOGIA 75 (4) 353 - 361 0011-4545 2010/12 [Refereed][Not invited]
    In oogamous brown algae, mitochondria and mitochondrial DNA (mtDNA) are maternally inherited. In this study, we attempted to clarify the timing of this process through morphological observations and molecular experiments using Undaria pinnatifida (Harvey) Suringar. Immunoelectron microscopy using an anti-DNA antibody indicated that mitochondria have their own mtDNA. The strain-specific single-germling PCR method showed that sperm mtDNA disappeared during the latter part of the one-cell zygote stage; digestion of sperm mitochondria, probably by autophagy, was observed in the one-celled zygote. These data show that in oogamous brown algae, sperm mtDNA is introduced into the cytoplasm of the egg with the mitochondria, and that sperm mitochondria and mtDNA are digested simultaneously, until initiation of the first division of the zygote.
  • Chikako Nagasato, Akira Inoue, Masashi Mizuno, Kazuki Kanazawa, Takao Ojima, Kazuo Okuda, Taizo Motomura
    PLANTA 232 (2) 287 - 298 0032-0935 2010/07 [Refereed][Not invited]
    During cytokinesis in brown algal cells, Golgi-derived vesicles (GVs) and flat cisternae (FCs) are involved in building the new cell partition membrane. In this study, we followed the membrane fusion process in Silvetia babingtonii zygotes using electron microscopy together with rapid freezing and freeze substitution. After mitosis, many FCs were formed around endoplasmic reticulum clusters and these then spread toward the future cytokinetic plane. Actin depolymerization using latrunculin B prevented the appearance of the FCs. Fusion of GVs to FCs resulted in structures that were thicker and more elongated (EFCs; expanded flat cisternae). Some complicated membranous structures (MN; membranous network) were formed by interconnection of EFCs and following the arrival of additional GVs. The MN grew into membranous sacs (MSs) as gaps between the MNs disappeared. The MSs were observed in patches along the cytokinetic plane. Neighboring MSs were united to form the new cell partition membrane. An immunocytochemical analysis indicated that fucoidan was synthesized in Golgi bodies and transported by vesicles to the future cytokinetic plane, where the vesicles fused with the FCs. Alginate was not detected until the MS phase. Incubation of sections with cellulase-gold showed that the cellulose content of the new cross wall was not comparable to that of the parent cell wall.
  • Makoto Terauchi, Atsushi Kato, Chikako Nagasato, Taizo Motomura
    PHYCOLOGICAL RESEARCH 58 (3) 217 - 221 1322-0829 2010/07 [Refereed][Not invited]
    P>A cDNA library was constructed from the chrysophycean alga, Ochromonas danica E. G. Pringsheim. 5'-end sequencing of about 600 cDNA clones yielded 476 authentic expressed sequence tags (EST) of which 275 showed significant matches (E-value < 10-4) to sequences in a public database. The annotation of these ESTs was carried out to assess subcellular localization of the putative proteins using several internet-accessible prediction programs for subcellular localization. These analyses revealed that putative plastid proteins in Ochromonas possess N-terminal bipartite presequences with a conserved phenylalanine at the N-terminus of the predicted transit peptide-like domains, similar to other 'red-lineage' secondary symbiotic organisms. The examination of sequences of 3'-UTR revealed that, similarly to chlorophyte algae, UGUAA may represent a putative polyadenylation signal in O. danica.
  • J. Mark Cock, Lieven Sterck, Pierre Rouze, Delphine Scornet, Andrew E. Allen, Grigoris Amoutzias, Veronique Anthouard, Francois Artiguenave, Jean-Marc Aury, Jonathan H. Badger, Bank Beszteri, Kenny Billiau, Eric Bonnet, John H. Bothwell, Chris Bowler, Catherine Boyen, Colin Brownlee, Carl J. Carrano, Benedicte Charrier, Ga Youn Cho, Susana M. Coelho, Jonas Collen, Erwan Corre, Corinne Da Silva, Ludovic Delage, Nicolas Delaroque, Simon M. Dittami, Sylvie Doulbeau, Marek Elias, Garry Farnham, Claire M. M. Gachon, Bernhard Gschloessl, Svenja Heesch, Kamel Jabbari, Claire Jubin, Hiroshi Kawai, Kei Kimura, Bernard Kloareg, Frithjof C. Kuepper, Daniel Lang, Aude Le Bail, Catherine Leblanc, Patrice Lerouge, Martin Lohr, Pascal J. Lopez, Cindy Martens, Florian Maumus, Gurvan Michel, Diego Miranda-Saavedra, Julia Morales, Herve Moreau, Taizo Motomura, Chikako Nagasato, Carolyn A. Napoli, David R. Nelson, Pi Nyvall-Collen, Akira F. Peters, Cyril Pommier, Philippe Potin, Julie Poulain, Hadi Quesneville, Betsy Read, Stefan A. Rensing, Andres Ritter, Sylvie Rousvoal, Manoj Samanta, Gaelle Samson, Declan C. Schroeder, Beatrice Segurens, Martina Strittmatter, Thierry Tonon, James W. Tregear, Klaus Valentin, Peter von Dassow, Takahiro Yamagishi, Yves Van de Peer, Patrick Wincker
    NATURE 465 (7298) 617 - 621 0028-0836 2010/06 [Refereed][Not invited]
    Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related(1). These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae(2-5), closely related to the kelps(6,7) (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic(2) approaches to explore these and other(4,5) aspects of brown algal biology further.
  • Taizo Motomura, Chikako Nagasato, Kei Kimura
    JOURNAL OF PLANT RESEARCH 123 (2) 185 - 192 0918-9440 2010/03 [Refereed][Not invited]
    Brown algae, together with diatoms and chrysophytes, are a member of the heterokonts. They have either a characteristic life cycle of diplohaplontic alternation of gametophytic and sporophytic generations that are isomorphic or heteromorphic, or a diplontic life cycle. Isogamy, anisogamy and oogamy have been recognized as the mode of sexual reproduction. Brown algae are the characteristic group having elaborated multicellular organization within the heterokonts. In this study, cytoplasmic inheritance of chloroplasts, mitochondria and centrioles was examined, with special focus on sexual reproduction and subsequent zygote development. In oogamy, chloroplasts and mitochondria are inherited maternally. In isogamy, chloroplasts in sporophyte cells are inherited biparentally (maternal or paternal); however, mitochondria (or mitochondrial DNA) derived from the female gamete only remained during zygote development after fertilization. Centrioles in zygotes are definitely derived from the male gamete, irrespective of the sexual reproduction pattern. Female centrioles in zygotes are selectively broken down within 1-2 h after fertilization. The remaining male centrioles play a crucial role as a part of the centrosome for microtubule organization, mitosis, determination of the cytokinetic plane and cytokinesis, as well as for maintaining multicellularity and regular morphogenesis in brown algae.
  • Kei Kimura, Chikako Nagasato, Kazuhiro Kogame, Taizo Motomura
    JOURNAL OF PHYCOLOGY 46 (1) 143 - 152 0022-3646 2010/02 [Refereed][Not invited]
    Mitochondrial DNA (mtDNA) of the isogamous brown alga Scytosiphon lomentaria (Lyngb.) Link is inherited maternally. We used molecular biological and morphological analyses to investigate the fate of male mitochondria. Ultrastructural observations showed that the number of 25 mitochondria in a zygote coincided with the number of mitochondria derived from male and female gametes. This number remained almost constant during the first cell division. Strain-specific PCR in single germlings suggested that mtDNA derived from the female gamete remained in the germling during development, while the male mtDNA gradually and selectively disappeared after the four-cell stage. One week after fertilization, male mtDNA had disappeared in sporophytic cells. Using bisulfite DNA modification and methylation mapping assays, we found that the degree of methylation on three analyzed sites of mtDNA was not different between male and female gametes, suggesting that maternal inheritance of mtDNA is not defined by its methylation. This study indicates that the mechanism of selective elimination of male mtDNA is present in each cell of a four-celled sporophyte and that it does not depend on different degrees of DNA methylation between male and female mtDNA.
  • 石油系燃料油汚染土壌のバイオレメディエーション-特に環境微生物学的なアプローチ-
    北山茂一, 原宏哉, 岩城美朝, 長里千香子, 本村泰三, 遠山忠, チャンヨンチョル, 菊池慎太郎
    環境技術 38 276 - 282 2009/10/01 [Refereed][Not invited]
  • Takahiro Yamagishi, Taizo Motomura, Chikako Nagasato, Hiroshi Kawai
    JOURNAL OF PHYCOLOGY 45 (5) 1110 - 1115 0022-3646 2009/10 [Refereed][Not invited]
    Two-dimensional (2-D) protein analysis of the mastigoneme fraction of the chromophyte alga Ochromonas danica E. G. Pringsh. showed the presence of several component proteins of the tubular mastigoneme. Adding to the reported gene Ocm1, three new genes (Ocm2, Ocm3, and Ocm4) belonging to the Ocm gene family were isolated using degenerate primers designed from predicted Ocm1 amino acid sequences. The predicted polypeptides encoded by Ocm2, Ocm3, and Ocm4 were smaller in size than Ocm1. However, they shared four highly conserved, cysteine-rich, epithelial growth factor (EGF)-like motifs, potentially involved in protein protein interaction. In addition, Ocm2, Ocm3, and Ocm4 showed homology to the SIG protein family in the centric diatom Thalassiosira weissflogii (Grunow) Fryxell et Hasle, which is up-regulated during early stages of sexual reproduction. Immunofluorescence analysis with a polyclonal antibody against the partial amino acid sequences of Ocm2, Ocm3, and Ocm4 showed that Ocm2 and Ocm3 were located in the basal segment region of mastigonemes attached on the surface of the anterior flagellum, and that Ocm4 was located within the tubular shaft portion similar to Ocm1.
  • Mie Ishikawa, Fumio Takahashi, Hisayoshi Nozaki, Chikako Nagasato, Taizo Motomura, Hironao Kataoka
    PLANTA 230 (3) 543 - 552 0032-0935 2009/08 [Refereed][Not invited]
    The new type blue light (BL) receptor aureochrome (AUREO) was recently discovered in a stramenopile alga, Vaucheria (Takahashi et al. Proc Natl Acad Sci USA 104(49):19625-19630, 2007). AUREO has a bZIP (basic region/leucine zipper) and BL-sensing light-oxygen-voltage (LOV) domain and functions as a BL-activated transcription factor. It mediates BL-induced branching and regulates the development of the sex organ in V. frigida. Although AUREO sequences have previously been found in Fucus and some diatoms, here we report that AUREO orthologs are commonly conserved in photosynthetic stramenopiles. Five AUREO orthologs were isolated from three stramenopile genera (Fucus, Ochromonas, and Chattonella). By BLAST search, several AUREO sequences were also detected in genomes in Aureococcus anophagefferens (Pelagophyceae). However, AUREO was not found in heterotrophic stramenopiles or in closely related phyla, such as haptophytes and cryptophytes, or in green plants. Stramenopiles do not possess phototropin, the well-known BL receptor for phototropism of green plants. From comparative analysis of LOV domains, together with kinship analysis of AUREO bZIP domains, AUREO can be regarded as the BL receptor specific to phototrophic stramenopiles. The evolution of AUREO and the phylogeny of LOV domains in stramenopiles and green plants are discussed.
  • Chika Ueki, Chikako Nagasato, Taizo Motomura, Naotsune Saga
    BOTANICA MARINA 52 (2) 129 - 139 0006-8055 2009/04 [Refereed][Not invited]
    We studied mitosis and cytokinesis during spermatogenesis in the red alga Porphyra yezoensis Ueda using electron microscopy with the cryofixation-freeze-substitution technique and by fluorescence microscopy using tubulin immunofluorescence and SYBR Gold staining. Spermatogenesis occurred along the blade margin with a series of cell divisions. During interphase, two nucleus-associated organelles (NAOs) were located close to the nuclear envelope and had a ring-on-ring morphology. In prophase, the NAOs migrated to the future mitotic poles. The nuclear envelope of prometaphase nuclei became deeply depressed below each NAO, and the two rings of the NAOs appeared to separate until early telophase. The chromosomes became aligned at the equator in metaphase, although individual chromosomes and their kinetochores were not clearly defined. The two rings of the NAO moved next to each other on the nuclear envelope during mid-telophase, and then NAO replication occurred. In late telophase, the pair of NAOs repositioned on the nuclear envelope. Cytokinesis started with furrowing of the plasma membrane.
  • Chikako Nagasato, Taizo Motomura
    JOURNAL OF PHYCOLOGY 45 (2) 404 - 412 0022-3646 2009/04 [Refereed][Not invited]
    In zygotes of the brown alga Scytosiphon lomentaria (Lyngb.) Link, cytokinesis proceeds by growth of membranous sacs, which are formed by fusion of Golgi vesicles and flat cisternae accumulated at the future cytokinetic plane. It has been reported that depolymerization of actin filaments by latrunculin B does not inhibit mitosis. However, this molecule prevents the formation of the actin plate, which appears at the region of intermingled microtubules from each centrosome just before and during cytokinesis. In this study, zygotes treated with latrunculin B were observed using EM. Remarkably, this reagent inhibited the formation of flat cisternae. Golgi vesicles gathered around the midzone between the two daughter nuclei and fused with the plasma membrane there. As a result, the plasma membrane invaginated, in a complicated manner, into the cytoplasm. However, these invaginations of the plasma membrane never produced a continuous partition membrane. The ultrastructure of zygotes treated with brefeldin A, which prevents Golgi-mediated secretion, was also examined. Flat cisternae appeared at the future cytokinetic plane, and a new cell partition membrane was formed. However, the partition membrane became thick, because it was filled with amorphous material rather than the normal rigid fibrous material. These results suggested that actin is involved in the formation of flat cisternae, where it is necessary for completion of the new cell partition membrane, and that Golgi vesicles may play an important role in the deposition of cell wall material.
  • Christos Katsaros, Taizo Motomura, Chikako Nagasato, Basil Galatis
    BOTANICA MARINA 52 (2) 150 - 161 0006-8055 2009/04 [Refereed][Not invited]
    We studied development of the cytokinetic diaphragm (i.e., the membranous septum formed during cytokinesis) in vegetative cells of the brown algae Sphacelaria rigidula, Halopteris congesta and Dictyota dichotoma after cryofixation-freeze-substitution. Cytokinesis began by the gathering of organelles and large vesicles between daughter nuclei following telophase. Subsequently, a thin cytoplasmic strand was formed along this plane, where endoplasmic reticulum (ER), dictyosome vesicles and particular membranous elements, the flat cisternae, were accumulated. Their fusion formed a patchy diaphragm with irregular gaps. Fine tubular channels perforated the diaphragm during all stages of its formation. Following diaphragm completion, cell wall material was deposited in it. The new walls had ER-free plasmodesmata. In D. dichotoma, diaphragm development did not follow a definite pattern, i.e., centripetal or centrifugal, a phenomenon also confirmed in H. congesta. In contrast, in apical cells of S. rigidula the diaphragm started developing from the periphery, growing to some extent centripetally. In these cells, local cell wall deposition was greatest at the division site. In apical cells in which cytokinesis was experimentally inhibited a ring of wall material was usually deposited at the cytokinetic plane.
  • Taizo Motomura, Chikako Nagasato
    BOTANICA MARINA 52 (2) 140 - 149 0006-8055 2009/04 [Refereed][Not invited]
    Functional (with centrioles) and non-functional (without centrioles) mitotic spindle formation was studied in Fucus distichus zygotes. In normally fertilized zygotes, a pair of centrioles derived from sperm existed at both mitotic poles. Both centrin and gamma-tubulin were associated with centrioles. In multipolar spindles of fertilized multinucleate eggs, mitotic poles with centrioles were stained with an anti-gamma-tubulin antibody, but the other poles were not, and cytokinesis proceeded abnormally. When karyogamy was blocked with colchicine, centrioles remained around the sperm nucleus. A monastral spindle or a bipolar, barrel-shaped spindle was formed on the egg nucleus; however, there were no centrioles at these mitotic poles. When cytoplasmic fragments containing only an egg or a sperm nucleus were separately prepared and cultured, the egg nucleus appeared to enter, but did not complete, mitosis. In cytoplasm containing only a sperm nucleus, mitosis and cytokinesis did not occur. We concluded that the egg nucleus has the potential to form a non-functional spindle without the sperm centrioles. However, this acentrosomal spindle was non-functional; mitosis remained at the stage of chromosome condensation and did not proceed to cytokinesis. Even though some cells proceeded to cytokinesis, they showed abnormal chromosome condensation.
  • Chika Ueki, Chikako Nagasato, Taizo Motomura, Naotsune Saga
    PHYCOLOGIA 47 (1) 5 - 11 0031-8884 2008/01 [Refereed][Not invited]
    Pit plug formation during conchosporogenesis in Porphyra yezoensis Ueda was studied with electron microscopy using freeze substitution. Just after nuclear division, cytokinesis started with furrowing of the septum. During furrowing, small vesicles were produced by projections of the plasma membrane in the space between the plasma membrane and the cell wall material and occasionally formed long chains. Afterwards, the plug core was gradually formed by endoplaslilic reticulum, becoming vertical to the septum. The plasma membrane expanded like a loop along the pit Plug from both sides of the furrowing septum. Lomasomes were located near the plasma membrane, beside the pit Plug. With maturation of conchosporangia, the number of lomasomes increased near the pit plug. P. yezoensis has a characteristic expanding process of the plasma membrane along the pit plug, which is unique in the red algae.
  • Atsuko Tanaka, Chikako Nagasato, Shinya Uwai, Taizo Motomura, Hiroshi Kawai
    PHYCOLOGICAL RESEARCH 55 (3) 203 - 213 1322-0829 2007/09 [Refereed][Not invited]
    Some taxa of brown algae have a so-called 'stellate' chloroplast arrangement composed of multiple chloroplasts arranged in a stellate configuration, or else a single chloroplast with radiating lobes. The fine structures of chloroplasts and pyrenoids have been studied, but the details of their membrane configurations as well as pyrenoid ontogeny have not been well understood. The ultrastructure of the single stellate chloroplast in Splachnidium rugosum and Scytothamnus australis were re-examined in the present study, as well as the stellate arrangement of chloroplasts in Asteronema ferruginea and Asterocladon interjectum, using freeze-substitution fixation. It was confirmed that the chloroplast envelope invaginated into the pyrenoid in Splachnidium rugosum, Scytothamnus australis and Asteronema ferruginea, but chloroplast endoplasmic reticulum (CER) remained on the surface of the chloroplast. The space between the invaginated chloroplast envelope and CER was filled with electron-dense material. In Asteronema ferruginea, CER surrounding each pyrenoid was closely appressed to the neighboring CER over the pyrenoids, so that the chloroplasts formed a stellate configuration; however, in the apical cells chloroplasts formed two or more loose groups, or were completely dispersed. The pyrenoids of Asterocladon interjectum did not have any invagination of the chloroplast envelope, but a unique membranous sac surrounded the pyrenoid complex and occasionally other organelles (e.g. mitochondria). Immunolocalization of beta-1,3-glucans showed that the membranous sac in Asterocladon interjectum did not contain photosynthetic products such as chrysolaminaran. Observations in the dividing cells of Splachnidium rugosum and Scytothamnus australis indicated that the pyrenoid in the center of the chloroplast enlarged and divided into two before or during chloroplast division.
  • Takahiro Yamagishi, Taizo Motomura, Chikako Nagasato, Atsushi Kato, Hiroshi Kawai
    JOURNAL OF PHYCOLOGY 43 (3) 519 - 527 0022-3646 2007/06 [Refereed][Not invited]
    The phylogenetic group stramenopiles refers to the systematic groups that possess tripartite tubular hairs (stramenopiles) on their flagella. There have been a number of studies describing the fine structure of these mastigonemes and a few studies isolating the component proteins; however, these proteins and their gene sequences have not yet been identified. In the present study, we identified a mastigoneme protein (Ocm1) of the chrysophycean alga Ochromonas danica Pringsh. (UTEX LB1298). Its corresponding gene, Ocm1, was identified by using degenerate primers that correspond to the partial amino acid sequences of a protein (85 kDa) obtained from a mastigoneme-rich fraction of isolated flagella. The polypeptide encoded by Ocm1 has four cysteine-rich, epithelial growth factor (EGF)-like motifs, potentially involved in protein-protein interactions. It lacks obvious hydrophobic regions characteristic of transmembrane domains, suggesting that this polypeptide is not likely a protein for anchoring the mastigoneme. In addition, a polyclonal antibody against Ocm1 labeled the area where the tubular shafts of the mastigonemes are located, but not the basal portion or the terminal filaments.
  • Chihiro Uemori, Chikako Nagasato, Atsushi Kato, Taizo Motomura
    PHYCOLOGICAL RESEARCH 54 (2) 133 - 139 1322-0829 2006/06 [Refereed][Not invited]
    The rhizoplast, a striated band elongating from the flagellar basal body to the nucleus, is conspicuous in cells of Ochromonas danica Prings. In interphase cells, it runs from the basal body of the anterior flagellum to the space between the nucleus and the Golgi body. In O. danica, the rhizoplast duplicates during mitosis and the two rhizoplasts serve as mitotic poles. In the present study, we reinvestigated mitosis of O. danica using transmission electron microscopy and immunofluorescence microscopy, especially focusing on the rhizoplast. The nuclear envelope became dispersed during metaphase, and the rhizoplasts from two sets of the flagellar basal bodies functioned as the mitotic poles. Immunofluorescence microscopy using anti-alpha-tubulin, anti-centrin and anti-gamma-tubulin antibodies showed that centrin molecules were localized at the flagellar basal bodies, whereas gamma-tubulin molecules were detected at the rhizoplast during the whole cell cycle.
  • Y Kato, K Kogame, C Nagasato, T Motomura
    PHYCOLOGICAL RESEARCH 54 (1) 65 - 71 1322-0829 2006/03 [Refereed][Not invited]
    Patterns of inheritance of chloroplasts and mitochondria were examined by fluorescence microscopy and haplotype genome markers in the isogamous brown alga Scytosiphon lomentaria (Lyngbye) Link. Germination of the zygote in this species was unilateral, the growing thallus developed entirely from the germ tube, and the original zygote cell did not develop except for the formation of a hair. Inheritance of chloroplasts was biparental, and partitioning of the two parental chloroplasts into the first sporophytic cells was accidental: either the maternal or the paternal chloroplast was migrated from the zygote into the germ tube cell, whereas the other chloroplast remained in the original cell. In contrast, the mitochondrial genome in all cells of the sporophyte came only from the female gamete (maternal inheritance). These inheritance patterns are similar to those of the isogamous brown alga Ectocarpus siliculosus (Dillwyn) Lyngbye. Maternal inheritance of mitochondria might be universal in brown algae.
  • C Nagasato
    JOURNAL OF PLANT RESEARCH 118 (6) 361 - 369 0918-9440 2005/12 [Refereed][Not invited]
    In brown algal cells, the centrosome, consisting of a pair of centrioles and the pericentriolar material, is primarily involved in the organization of microtubules (MTs) throughout the cell cycle. In motile cells, the centrioles participate in the formation of flagellar axoneme as flagellar basal bodies, and in somatic cells they play a crucial role in many cellular activities as a part of the centrosome. With respect to the role of the centrosome as a microtubule organizing center (MTOC), brown algal cells resemble animal cells. In most animal fertilization processes, the sperm cell introduces centrioles, the core of the centrosome, into the egg cytoplasm. In this study, the behavior of centrioles from gametogenesis and fertilization to the first cell division of the zygote was examined in the three sexual reproduction patterns occurring in brown algae, i.e., oogamy, anisogamy and isogamy, by electron- and immunofluorescence-microscopy. The pair of centrioles contained in somatic cells was shown to be derived from the male gamete, irrespective of the sexual reproductive pattern. The paternally derived centrioles were duplicated before mitosis and were involved in spindle pole formation. Moreover, MTs from the centrosome play a crucial role in the process of cytokinesis, as the position of centrosomes accompanying daughter nuclei seems to determine the cytokinetic plane. A new approach to clarifying the mode of cytokinesis in brown algae is presented in this study.
  • S Uwai, C Nagasato, T Motomura, K Kogame
    EUROPEAN JOURNAL OF PHYCOLOGY 40 (2) 179 - 194 0967-0262 2005/05 [Refereed][Not invited]
    A small prostrate filamentous brown alga, isolated from the warm temperate Pacific coast of Japan, was cultured to investigate its life history, morphology, ultrastructure and molecular phylogenetic position. The isolate had an isomorphic, diphasic life history with anisogamous sexual reproduction. Gametogenesis was regulated by temperature and occurred only at temperatures <= 14 degrees C. At higher temperatures, gametophytes reproduced by means of asexual zoids. All swarmers from plurilocular and unilocular zoidangia lacked an eyespot. Both sporophytes and gametophytes had oligostichous filamentous axes, lateral hairs with a basal sheath and no erect thalli. Three to eight oblong chloroplasts, each with a protruding pyrenoid, aggregated to form a stellate chloroplast configuration. All these morphological features suggested that this alga belongs to the genus Asterocladon. Plurilocular gametangia produced in an intercalary or terminal position and zoids lacking eyespots, are, however, unlike those of Asterocladon lobatum, formerly the only member of the genus. Therefore, we described the alga as a new taxon, Asterocladon interjectum sp. nov. Molecular phylogenetic analyses based on the large RUBISCO subunit ( rbcL) and partial SSU nuclear ribosomal RNA gene sequences showed that A. interjectum, A. lobatum and Asteronema rhodochortonoides together formed a monophyletic clade, sister to the Ectocarpales sensu lato. Because the molecular phylogenetic analyses showed Asteronema to be paraphyletic, but monophyly of Asterocladon spp. and Asteronema rhodochortonoides was supported by the absence of cytoplasmic invaginations in pyrenoids, Asteronema rhodochortonoides was transferred to Asterocladon and an emended generic circumscription of Asterocladon was included.
  • C Nagasato, T Motomura
    CELL MOTILITY AND THE CYTOSKELETON 59 (2) 109 - 118 0886-1544 2004/10 [Refereed][Not invited]
    In brown algal fertilization, a pair of centrioles is derived from the male gamete, irrespective of the Sexual reproduction pattern, i.e., isogamy, anisogamy, or oogamy. In this study, the manner in which the maternal centriole structure is destroyed in early zygotes of the isogamous brown alga Scytosiphon lomentaria was examined by electron microscopy. At fertilization, the zygote had two pairs of centrioles (flagellar basal bodies) derived from motile male and female gametes, and there was no morphological difference between the two pairs. The flagellar basal plate and the axonemal microtubules were still connected with the distal end of centrioles. Ultrastructural observations showed that the integrity of maternal-derived centrioles began to degenerate even in the 1-h-old zygote. At that time. the cylinder of triplet microtubules of the maternal centrioles became shorter from the distal end, and a section passing through the centrioles indicated that a part of the nine triplets Of microtubules changed into doublet or singlet microtubules by degeneration of B and/or C tubules. In 2-h-old zygote, there was no trace of maternal centrioles ultrastructurally, and only the paternal centrioles remained. Further, reduction of centrin accompanying destruction of the maternal centrioles was examined in immunofluorescence microscopy. Centrin localized at the paternal and the maternal centrioles had the same fluorescence intensity in the early zygotes. At 4-6 h after fertilization, two spots indicating centrin localization showec different fluorescence intensity. Later, the weaker spot disappeared completely. These results showed that there is a difference in time between the destruction of the centriolar cylinders and the reduction of centrin molecules around them.(C) 2004 Wiley-Liss. Inc.
  • C Nagasato, C Uemori, A Kato, T Motomura
    PHYCOLOGICAL RESEARCH 52 (3) 266 - 272 1322-0829 2004/09 [Refereed][Not invited]
    Centrin, the EF-hand Ca2+-binding protein is localized at the basal apparatus of flagella and in centrioles in many eukaryotic cells. In the present study, centrin genes of the heterokont algae have been clarified for the first time. We isolated and analyzed cDNA and genomic DNA of centrin genes from the crysophycean alga Ochromonas danica Prings (UTEX LB1298) and the brown alga Scytosiphon lomentaria (Lyngbye) Link. The centrin gene of Ochromonas contained an open reading frame of 163 amino acids. The deduced protein, named Odcen, exhibited 85%, 78% and 59% homology to Chlamydomonas, human and Arabidopsis centrin, respectively. The centrin genes of Scytosiphon contained an open reading frame of 164 amino acids. The deduced protein, named Slcen, exhibited 84%, 77% and 59% homology to Chlamydomonas, human and Arabidopsis centrin, respectively. Both Odcen and Slcen possessed N-terminal extensions before the conserved amino acid among various centrins, four EF-hand domains and an aromatic amino acid at the C-terminus. Southern blot hybridization suggested that the centrin gene occurs as a single copy gene in both Ochromonas and Scytosiphon genomes. Comparison of the sequence of the cDNA and the genomic DNA revealed that the Odcen gene was split into three fragments by introns and Slcen gene consisted of five fragments. The junctions of all introns of both genes conformed to the GT-AG rule. The introns of Slcen gene were considerably long and, as a result, the Slcen gene was approximately seven times longer than Odcen gene.
  • T Motomura, C Nagasato
    HYDROBIOLOGIA 512 (1-3) 171 - 176 0018-8158 2004/01 [Refereed][Not invited]
    Regulation of the first spindle formation in brown algal zygotes was described. It is well known that there are three types of sexual reproduction in brown algae; isogamy, anisogamy and oogamy. Paternal inheritance of centrioles can be observed in all these cases, similar to animal fertilization. In isogamy and anisogamy, female centrioles (= flagellar basal bodies) selectively disappear and male centrioles remain after fertilization. In a typical oogamy (e.g. fucoid members), liberated egg does not have centrioles, and sperm centrioles are introduced in zygote. Participation of sperm centrioles to the spindle formation in zygotes was also described using Fucus distichus as a model system. Sperm centrioles function as a part of centrosome, namely microtubule organizing center, in zygote. Therefore, they have a crucial role in the spindle formation. Observations on the spindle formation in polygyny and karyogamy-blocked zygotes strongly suggest that egg nucleus can form a mitotic spindle by itself without centrosome, even though the resulting spindles are of abnormal shapes.
  • Nuclear histone proteins of gametes in brown algae. The Japanese Journal of Phycology (Sorui) 52 (supplement issue)
    Yoshikawa S, Nagasato C, Makino Y, Murakami A, Kawai H, Ichimura T, Motomura T
    Japanese Journal of Phycology (Sorui) 52 123 - 127 2004 [Refereed][Not invited]
  • Chikako Nagasato, Shinya Yoshikawa, Masakane Yamashita, Hiroshi Kawai, Taizo Motomura
    Journal of Phycology 39 (6) 1172 - 1180 0022-3646 2003/12 [Refereed][Not invited]
    Vegetative cells of the brown alga Scytosiphon lomentaria (Lyngbye) Link characteristically have only one chloroplast with a prominent protruding pyrenoid, whereas zygotes have both paternal and maternal chloroplasts. In zygotes, before cell and chloroplast division, each chloroplast has an old and a new pyrenoid. In this study, we raised a polyclonal antibody to RUBISCO and examined the distribution of RUBISCO by immunofluorescence microscopy, focusing on new pyrenoid formation in vegetative cells of gametophytes and zygotes in Scytosiphon. In interphase, only one old pyrenoid was positively indicated by anti-RUBISCO antibody in vegetative cells of gametophytes. From mid-S phase, small fluorescence aggregates reflecting RUBISCO localization started to appear at stroma positions other than adjacent to the old protruding pyrenoid. The fluorescent spots eventually coalesced into a protrusion into the adjacent cytoplasm. We also used inhibitors to clarify the relationship between the cell cycle and new pyrenoid formation, using zygotes after fertilization. When DNA replication was blocked by aphidicolin, new pyrenoid formation was also inhibited. Washing out aphidicolin permitted new pyrenoid formation with the progression of the cell cycle. When mitosis was prolonged by nocodazole, which disrupted the spindle microtubules, the fluorescent masses indicating RUBISCO localization continued to increase when compared with pyrenoid formation in untreated zygotes. During treatment with chloramphenicol, mitosis and cytokinesis were completed. However, there was no occurrence of new RUBISCO localization within the chloroplast stroma beyond the old pyrenoid. From these observations, it seems clear that new pyrenoid formation in the brown alga Scytosiphon depends on the cell cycle.
  • Shinya Yoshikawa, Chikako Nagasato, Terunobu Ichimura, Taizo Motomura
    Phycological Research 51 (2) 77 - 82 1322-0829 2003 [Refereed][Not invited]
    Morphological changes and chromatin condensation of sperm nuclei were observed during spermatogenesis in the fucalean brown alga Cystoseira hakodatensis (Yendo) Fensholt. Ultrastructural studies have shown that the mature spermatozoid has an elongated and concave nucleus with condensed chromatin. The morphological changes and the chromatin condensation process during spermatogenesis was observed. Nuclear size decreased in two stages during spermatogenesis. During the first stage, spherical nuclei decreased in size as they were undergoing meiotic divisions and the subsequent mitoses within the antheridium. During the second stage, the morphological transformation from a spherical into an elongated nucleus occurred. Afterwards, chromatin condensed at the periphery in each nucleus, and chromatin-free regions were observed in the center of the nucleus. These chromatin-free regions in the center of nucleus were compressed by the peripheral chromatin-condensed region. As the result, the elongated and concave nucleus of the mature sperm consisted of uniformly well-condensed chromatin.
  • C Nagasato, T Motomura
    JOURNAL OF PHYCOLOGY 38 (4) 800 - 806 0022-3646 2002/08 [Refereed][Not invited]
    The Seytosiphon lomentaria (Lyngbye) Link cell characteristically has only one chloroplast with a prominent protruding pyrenoid. We observed the appearance of a new pyrenoid in each chloroplast during first mitosis in zygotes of S. lomentaria, using the freeze substitution technique. At first, a pyrenoid matrix appeared within the outermost stroma, in which thylakoid triplets and ribosomes were absent. At this time, the surface of this part remained smooth. The old pyrenoid was covered with a pyrenoid cap on the cytoplasmic side, whereas there was no pyrenoid cap on the new pyrenoid before protrusion. Irregularly shaped membranous sacs containing fine granular materials associated with the cytoplasmic side of the new pyrenoid. The sacs fused with each other and changed conformation and finally transformed into the pyrenoid cap. The new pyrenoid gradually protruded toward the cytoplasm, and the new pyrenoid cap became curved along the surface of pyrenoid. Cytokinesis occurred, and each chloroplast had two prominent protruding pyrenoids in two-celled zygotes. We examined immunolocalization of beta-1,3-glucans within the pyrenoid cap with a monoclonal antibody, using EM. Gold particles indicating localization of beta-1,3-glucans were detected in vacuoles but never in the pyrenoid cap. This observation suggests that the pyrenoid cap in brown algae contains no photosynthetic products such as polysaccharide.
  • C Nagasato, T Motomura
    JOURNAL OF CELL SCIENCE 115 (12) 2541 - 2548 0021-9533 2002/06 [Refereed][Not invited]
    We examined the relationship between the spindle orientation and the determination site of cytokinesis in brown algal cells using polyspermic zygotes of Scytosiphon lomentaria. When two male gametes fuse with one female gamete, the zygote has two pairs of centrioles derived from male gametes and three chloroplasts from two male and one female gametes. Just before mitosis, two pairs of centrioles duplicate and migrate towards the future mitotic poles. Spindle MTs develop and three or four spindle poles are formed. In a tri-polar spindle, one pair of centrioles shifts away from the spindle, otherwise, two pairs of centrioles exist adjoining at one spindle pole. Chromosomes arrange at several equators of the spindle. As a result of these multipolar mitoses, three or four daughter nuclei developed. Subsequently, these daughter nuclei form a line along the long axis of the cell. Cell partition always takes place between daughter nuclei, perpendicular to the long axis of the cell. Three or four daughter cells are produced by cytokinesis. Some of the daughter cells after cytokinesis do not have a nucleus, but all of them always contain the centrosome and chloroplast. Therefore, the number of daughter cells always coincides with the number of centrosomes or microtubule organizing centers (MTOCs). These results show that the cytokinetic plane in the brown algae is determined by the position of centrosomes after mitosis and is not dependent on the spindle position.
  • Shinya Yoshikawa, Chikako Nagasato, Yumiko Makino, Akio Murakami, Hiroshi Kawai, Terunobu Ichimura, Taizo Motomura
    Journal of Phycology 38 (2) 318 - 324 0022-3646 2002/01/01 [Refereed][Not invited]
    Nuclear basic proteins (histones) were studied in male and female gametes of the isogamous brown algae, Colpomenia bullosa (Saunders) Yamada and Analipus japonicus (Harvey) Wynne and sperm of the oogamous Cystoseira hakodatensis (Yendo) Fensholt by using SDS- and AUT-PAGE. Four major core histones and several linker histone H1s were detected by electrophoresis. Each of the core histones was identified by amino acid sequence analysis and peptide mapping. Electrophoresis patterns of histones were the same in male and female gametes and quite similar between the two species. The composition of histone H1s in conspicuously condensed sperm nuclei of C. hakodatensis was different from that in isogamous gametes. Electrophoresis after micrococcal nuclease digestion of chromatin in male and female gamete nuclei of C. bullosa and A. japonicus and sperm of C. hakodatensis resulted in regular ladder patterns of DNA fragments (ca. 200 base pair). The chromatin of the brown algal gametes thus has the typical nucleosome structure. These results showed that chromatin condensation in sperm nuclei of C. hakodatensis was associated with a modification of linker histone H1 but not by change of core histones, replacement by other basic proteins, changes of repeating patterns, or disappearance of nucleosomes.
  • C Nagasato, T Motomura
    PROTOPLASMA 219 (3-4) 140 - 149 0033-183X 2002 [Refereed][Not invited]
    The ultrastructure of mitosis and cytokinesis in Scytosiphon lomentaria (Lyngbye) Link zygotes was studied by freeze fixation and substitution. During mitosis, the nuclear envelope remained mostly intact. Spindle microtubules (MTs) from the centrosome passed through the gaps of the nuclear envelope and entered the nucleoplasm. In anaphase and telophase, two daughter chromosome masses were partially surrounded with endoplasmic reticulum. After telophase, the nuclear envelope was reconstructed and two daughter nuclei formed. Then, several large vacuoles occupied the space between the daughter nuclei. MTs from the centrosomes extended toward the mid-plane between two daughter nuclei, among the vacuoles. At that time, Golgi bodies near the centrosome actively produced many vesicles. Midway between the daughter nuclei, small globular vesicles and tubular cisternae accumulated. These vesicles derived from Golgi bodies were transported from the centrosome to the future division plane. Cytokinesis then proceeded by fusion of these vesicles, but not by a furrowing of the plasma membrane. After completion of the continuity with the plasma membrane, cell wall material was deposited between the plasma membranes. The tubular cisternae were still observed at the periphery of the newly formed septum. Microfilaments could not be observed by this procedure. We conclude that cytokinesis in the brown algae proceeds by fusion of Golgi vesicles and tubular cisternae, not by a furrowing of the plasma membrane.
  • C Nagasato, T Motomura, T Ichimura
    PHYCOLOGIA 40 (5) 411 - 420 0031-8884 2001/09 [Refereed][Not invited]
    Oogenesis in Silvetia babingtonii, Cystoseira hakodatensis and Sargassum confusum, especially nuclear behaviour and the degeneration of excess nuclei, was studied using electron and immunofluorescence microscopy. During oogenesis, meiosis and mitosis occurred without cell division, and eight nuclei temporarily coexisted in the oogonium. In the oogonium of Silvetia babingtonii, the eight nuclei were at first scattered. Two of them migrated to opposite sides of the oogonium and six to the centre. The six nuclei were finally extruded during the cytokinesis that precedes the formation of the two eggs. The nuclear envelope, the nucleoplasmic region and the nucleolus could not be recognized in these nuclei after extrusion. In the oogonium of C. hakodatensis, during the differentiation of the single egg, the seven excess nuclei were extruded from the oogonial cytoplasm as small cells containing several mitochondria, vesicles and a centriole but no chloroplasts. The nuclear envelope and a nucleolus were clearly recognizable. After extrusion, the small extruded cells formed cell walls. In the egg of Sargassum confustum, eight nuclei remained throughout maturation. After plasmogamy, however, the sperm nucleus fused with one of the eight nuclei, and the other seven nuclei then gradually degenerated during the development of the zygote. When the zygote nucleus entered the first mitosis, chromosomal condensation occurred also in the other nuclei, but a mitotic spindle was formed only for the zygote nucleus. The degenerating nuclei could still be observed even in the two-celled zygote. These cytological observations confirm earlier observations that oogenesis is quite different among members of the Fucales and will have significance for considerations of phylogenetic relationships within this group.
  • Motomura T, Nagasato C, Komeda Y, Okuda K
    Journal of Phycology 37 783 - 792 2001 [Refereed][Not invited]
  • C Nagasato, T Motomura, T Ichimura
    EUROPEAN JOURNAL OF PHYCOLOGY 35 (4) 339 - 347 0967-0262 2000/11 [Refereed][Not invited]
    The first spindle formation in karyogamy-blocked zygotes in the isogamous brown alga Scytosiphon lomentaria was studied by electron and immunofluorescence microscopy using anti-centrin and anti-beta -tubulin antibodies. Zygotes blocked in karyogamy by incubation at high temperature (22 degreesC) were compared with normal zygotes incubated at 14 degreesC. In normal zygotes, after the disappearance of female gamete centrioles. centrioles from the male gamete duplicated and migrated to both poles in the metaphase, and a bipolar spindle was formed. The nuclear envelope was almost intact except at the poles. In karyogamy-blocked zygotes of S. lomentaria, both DNA synthesis and chromosomal condensation occurred in the male and female nuclei. A bipolar mitotic spindle with a pair of centrioles at each of two poles could be observed in the male nucleus, but not in the female nucleus. In some cases, after a pair of centrioles derived from the male gamete duplicated and separated, one of the two pairs migrated towards the female nucleus. In this case, a monopolar spindle was formed independently in each of the female and male nuclei, In addition to the monopolar spindle, a bipolar spindle was formed lying across the unfused male and female nuclei. Male and female chromosomes were intermixed and some of them were incorporated into the spindle. After cytokinesis of the normal and karyogamy-blocked zygotes, two daughter cells, each with one nucleus and one chloroplast, were formed.
  • C Nagasato, T Motomura, T Ichimura
    PHYCOLOGIA 39 (2) 163 - 166 0031-8884 2000/03 [Refereed][Not invited]
    Unfertilized eggs of Focus distichus subsp. evanescens developed parthenogenetically in laboratory culture. Some of the eggs (< 10%) secreted cell wall materials in 14 degrees C, long-day conditions. Rhizoid elongation tin < 1% of unfertilized eggs) and chromosome condensation could be observed starting three days after inoculation, but the mitotic spindle was abnormal and generally lacked centrioles, although rarely these were present. Cytokinesis occurred in some parthenogenetic eggs.
  • C Nagasato, T Motomura, T Ichimura
    JOURNAL OF PHYCOLOGY 35 (6) 1246 - 1252 0022-3646 1999/12 [Refereed][Not invited]
    Karyogamy was inhibited by heat stress in zygotes of Scytosiphon lomentaria (Lyngbye) Link (isogamy), Cutleria cylindrica Okamura (anisogamy), and Fucus distichus subsp, evanescens (C. Agardh) Powell (oogamy), Although high temperatures did not inhibit migration of the male and female nuclei, nuclear envelope fusion was blocked. The ultrastructural stage at which karyogamy was inhibited varied among these species. In S. lomentaria, the outer membranes fused with each other, but the inner membranes did not fuse, Partial fusion of the nuclear envelope occurred in C, cylindrica, In F, distichus, the block of karyogamy at high temperature was incomplete, and nuclear fusion proceeded gradually, The block to karyogamy in S, lomentaria zygotes was reversible, and karyogamy proceeded when zygotes were transferred from 22 degrees to 14 degrees C, Experiments using inhibitors suggested that proteins that might be formed de novo after fertilization do not participate in karyogamy or its inhibition at either 14 degrees or 22 degrees C.
  • C Nagasato, T Motomura, T Ichimura
    DEVELOPMENTAL BIOLOGY 208 (1) 200 - 209 0012-1606 1999/04 [Refereed][Not invited]
    The influence of centrioles, derived from the sperm flagellar basal bodies, and the centrosomal material (MTOCs) on spindle formation in the brown alga Fucus distichus (oogamous) was studied by immunofluorescence microscopy using anti-centrin and anti-beta-tubulin antibodies In contrast to a bipolar spindle, which is formed after normal fertilization, a multipolar spindle was formed in polyspermic zygote. The number of mitotic poles in polyspermic zygotes was double the number of sperm involved in fertilization. As an anti-centrin staining spot (centrioles) was located at these poles, the multipolar spindles in polyspermic zygotes were produced by the supplementary centrioles. When anucleate egg fragments were fertilized, chromosome condensation and mitosis did not occur in the sperm nucleus. Two anti-centrin staining spots could be detected, microtubules (MTs) radiated from nearby, but the mitotic spindle was never produced. When a single sperm fertilized multinucleate eggs (polygyny), abnormal spindles were also observed. In addition to two mitotic poles containing anti-centrin staining spots, extra mitotic poles without anti-centrin staining spots were also formed, and as a result multipolar spindles were formed. When karyogamy was blocked with colchicine, it became clear that the egg nucleus proceeded independently into mitosis accompanying chromosome condensation. A monoastral spindle could be frequently observed, and in rare cases a barrel-shaped spindle was formed. However, when a sperm nucleus was located near an egg nucleus, the two anti-centrin staining spots shifted to the egg nucleus from the sperm nucleus. In this case, a normal spindle was formed, the egg chromosomes arranged at the equator, and the associated MTs elongated from one pole of the egg spindle toward the sperm chromosomes which were scattered. From these results, it became clear that paternal centrioles derived from the sperm have a crucial role in spindle formation in the brown algae, such as they do during animal fertilization. However, paternal centrioles were not adequate for the functional centrosome during spindle formation. We speculated that centrosomal materials from the egg cytoplasm aggregate around the sperm centrioles and are needed for centrosomal activation. (C) 1999 Academic Press.
  • Chikako Nagasato, Taizo Motomura, Terunobu Ichimura
    Phycological Research 46 (3) 191 - 198 1322-0829 1998 [Refereed][Not invited]
    The behavior of centrioles in zygotes and female gametes developing parthenogenetically in the anisogamous brown alga Cutleria cylindrica Okamura was studied using electron and immunofluorescence microscopy. Two pairs of centrioles, detected using anti-centrin antibody, were observed in the vicinity of the male and female nuclei, respectively, just after plasmogamy. The fluorescence intensity of one of the two centrin foci became weak 6 h after plasmogamy and finally disappeared. It was impossible to determine whether the male- or female-derived centrioles disappeared in zygotes, because there was nothing to detect morphological differences between the two centrioles. However, a prominent anti-centrin staining focus was located at the condensed male nucleus in zygotes in which karyogamy had not occurred yet. As a result, it was considered that the maternally inherited centrioles had selectively disappeared during development in C. cylindrica. The paternal inheritance of centrioles in zygotes was also confirmed by electron microscopy. Considering previous observations from oogamous and isogamous species of brown algae, we concluded that the paternal inheritance of centrioles could be universal in the brown algae.
  • Bisgrove, SR, C Nagasato, T Motomura, DL Kropf
    JOURNAL OF PHYCOLOGY 33 (5) 823 - 829 0022-3646 1997/10 [Refereed][Not invited]
    Antibodies that recognize the centrosome-associated protein centrin were used to characterize centrosomal origin and positioning during fertilization and the first cell cycle in Fucus distichus subsp. evanescens (C. Agardh) Powell and Pelvetia compressa (J. Agardh) Be Tent. Centrin was identified in sperm, eggs, and zygotes on protein blots, indicating the protein is present in both gametes. Using immunofluorescence microscopy, centrin was found in discrete foci in sperm. In contrast, eggs lack centrosomes and centrin was not detectable by immunofluorescence, indicating that centrin was probably dispersed in the cytoplasm. Two foci of centrin were present on the nuclear envelope of zygotes, but microtubules remained dispersed over the zygotic nucleus. Centrin foci separated over the nuclear envelope as the first cell cycle progressed. Microtubules became concentrated at the centrin foci to form centrosomes that gave rise to the spindle poles at mitosis.


Awards & Honors

  • 2019 国際藻類学会 国際藻類学会論文賞
  • 2004 日本植物学会 日本植物学会奨励賞
    受賞者: 長里千香子
  • 2001 第7回国際藻類学会議 The George F. Papenfuss Poster Award
    受賞者: Chikako Nagasato
  • 1998 日本藻類学会 日本藻類学会論文賞
    受賞者: 長里千香子

Research Grants & Projects

Educational Activities

Teaching Experience

  • Advanced Course in Biodiversity Science I
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 群集生態学・生態系・統計モデリング・一般化線形モデル community ecology, ecosystem, statistical modeling, generalized linear model (GLM)
  • Special Lecture in Biosphere Science II
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : Aquatic Biology, Marine Ecology, Oceanography
  • Special Course in Field Science I
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : フィールド科学、森林圏、水圏、耕地圏、生物学、生態学、資源・生態系管理 field science, forest ecosystem, aquatic ecosystem, agricultural ecosystem, biology, ecology, resource and ecosystem management
  • Special Course in Field Science II
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : フィールド科学、森林圏、水圏、耕地圏、生物学、生態学、資源・生態系管理 field science, forest ecosystem, aquatic ecosystem, agricultural ecosystem, biology, ecology, resource and ecosystem management
  • Advanced Course in Aquatic Biology I
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 水圏生物 藻類 海草類 プランクトン 細胞 発生 環境適応 生理生態学 群集生態学 生態系生態学
  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : biodiversity, cell structure, cellular response, ecology, macroalgae, microscopy, phylogenetics
  • Fundamental Course in Field Sciences
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 生物資源創成、共生生態系保全、持続的生物生産、生物多様性、生態系機能、生物群集生態 Bio-resources development, Ecosystem conservation, Sustainable bio-production, Biodiversity, Ecosystem function, Population and community ecology
  • The World of Science and Technology
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 現代生物科学,21世紀に生物科学が解決しなければならない課題,生体高分子,細胞の構造と機能,エネルギー代謝,細胞の成長と分裂,遺伝現象と遺伝子発現制御
  • Environment and People
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 海、河川、生命、細胞、遺伝子、魚、海藻、微生物、代謝、進化
  • Freshman Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 洞爺湖の環境、有珠山噴火、有珠山植生回復、海藻の生態、森林の生態
  • Freshman Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : フィールド、体験型、環境科学、自然、産業
  • Laboratory Course in Phycology
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 海藻類、生活史、生態学、生理学、発生学、形態観察、電子顕微鏡
  • Laboratory Course in Phycology
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 理学部
  • Arts and Science Courses in English 2
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 国際本部
    キーワード : Ecosystem conservation, Sustainable bioproduction, Biodiversity, Material cycling, Harmonizable relation between human and environment
  • English Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 生態系保全、持続的生物生産、生物多様性、物質循環、人間環境共生系
  • General Education Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 総合教育部
    キーワード : 生態系保全、持続的生物生産、生物多様性、物質循環、人間環境共生系
  • General Education Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 現代日本学プログラム課程
    キーワード : 生態系保全、持続的生物生産、生物多様性、物質循環、人間環境共生系
  • Environment and People
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 生物資源創成、共生生態系保全、持続的生物生産、生物多様性、生態系機能、生物群集生態

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