研究者データベース

市原 健介(イチハラ ケンスケ)
北方生物圏フィールド科学センター 水圏ステーション 室蘭臨海実験所
助教

基本情報

所属

  • 北方生物圏フィールド科学センター 水圏ステーション 室蘭臨海実験所

職名

  • 助教

学位

  • 博士(理学)(北海道大学)

科研費研究者番号

  • 60610095

J-Global ID

研究キーワード

  • 無性生殖   有性生殖   環境適応   進化   藻類   

研究分野

  • ライフサイエンス / 多様性生物学、分類学

職歴

  • 2021年04月 - 現在 北海道大学 北方生物圏フィールド科学センター 水圏ステーション 室蘭臨海実験所 助教
  • 2017年04月 - 2021年03月 北海道大学 北方生物圏フィールド科学センター 水圏ステーション 室蘭臨海実験所 特任助教
  • 2016年 - 2017年 専修大学 商学部 非常勤講師
  • 2014年 - 2017年 東京大学 大学院新領域創成科学研究科 学振特別研究員(PD)
  • 2015年06月 - 2016年06月 東邦大学 理学部 非常勤講師
  • 2013年 - 2014年 日本女子大学 理学部 学術研究員
  • 2011年 - 2013年 東邦大学 理学部 博士研究員
  • 2008年 - 2011年 北海道大学 大学院理学院 学振特別研究員(DC1)

研究活動情報

論文

  • Kensuke Ichihara, Tomokazu Yamazaki, Shigeyuki Kawano
    Phycological Research 70 1 50 - 56 2022年01月 [査読有り][通常論文]
     
    Although the green seaweed Ulva is one of the most common seaweeds in the coastal regions with well-studied ecological characteristics, few reverse genetic technologies have been developed for it. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system is a simple genome-editing technology based on a ribonucleoprotein (RNP) complex composed of an endonuclease and programmable RNA to target particular DNA sequences. Genome editing makes it possible to generate mutations on a target gene in non-model organisms without established transgenic technologies. In this study, we applied the CRISPR-Cas9 RNP genome-editing system to the green seaweed Ulva prolifera, using polyethylene glycol (PEG)-mediated transfection. Our experimental system disrupts a single gene (UpAPT) encoding adenine phosphoribosyl transferase (APT) and generates a resistant phenotype for gametophytes cultured in a medium with toxic compound 2-fluoroadenine. The PEG-mediated transfection used for gametes resulted in 2-fluoroadenine-resistant strains containing short indels or substitutions on UpAPT. Our results showed that the CRISPR-Cas9 system with PEG-mediated transfection was efficient for genome editing in Ulva.
  • Rina Yonamine, Kensuke Ichihara, Shiro Tsuyuzaki, Cécile Hervé, Taizo Motomura, Chikako Nagasato
    Journal of phycology 57 4 1356 - 1367 2021年05月01日 [査読有り]
     
    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.
  • Visualization of Gamete Mating Structure of Marine Green Alga by FE-SEM.
    Shinichi Miyamura, Kensuke Ichihara, Tomokazu Yamazaki, Kazuyoshi Kuwano & Shigeyuki Kawano.
    Cytologia 84 3 191 - 192 2019年09月 [査読有り][通常論文]
  • Ichihara K, Yamazaki T, Miyamura S, Hiraoka M, Kawano S
    Scientific reports 9 1 13523  2019年09月 [査読有り][通常論文]
  • Shahlizah Sahul Hamid, Masataka Wakayama, Kensuke Ichihara, Katsutoshi Sakurai, Yujin Ashino, Rie Kadowaki, Tomoyoshi Soga, Masaru Tomita
    Planta 2019年01月01日 [査読有り][通常論文]
     
    © 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Main Conclusion: Among seaweed groups, brown algae had characteristically high concentrations of mannitol, and green algae were characterised by fructose. In red algae, metabolite profiles of individual species should be evaluated. Seaweeds are metabolically different from terrestrial plants. However, general metabolite profiles of the three major seaweed groups, the brown, red, and green algae, and the effect of various extraction methods on metabolite profiling results have not been comprehensively explored. In this study, we evaluated the water-soluble metabolites in four brown, five red, and two green algae species collected from two sites in northern Japan, located in the Sea of Japan and the Pacific Ocean. Freeze-dried seaweed samples were processed by methanol–water extraction with or without chloroform and analysed by capillary electrophoresis- and liquid chromatography-mass spectrometry for metabolite characterisation. The metabolite concentration profiles showed distinctive characteristic depends on species and taxonomic groups, whereas the extraction methods did not have a significant effect. Taxonomic differences between the various seaweed metabolite profiles were well defined using only sugar metabolites but no other major compound types. Mannitol was the main sugar metabolites in brown algae, whereas fructose, sucrose, and glucose were found at high concentrations in green algae. In red algae, individual species had some characteristic metabolites, such as sorbitol in Pyropia pseudolinearis and panose in Dasya sessilis. The metabolite profiles generated in this study will be a resource and provide guidance for nutraceutical research studies because the information about metabolites in seaweeds is still very limited compared to that of terrestrial plants.
  • Jianjun Cui, Alvin P. Monotilla, Wenrong Zhu, Yoshihito Takano, Satoshi Shimada, Kensuke Ichihara, Tohru Matsui, Peimin He, Masanori Hiraoka
    Phycologia 57 692 - 704 2018年09月21日 [査読有り][通常論文]
     
    © 2018 International Phycological Society. Since 2008, the green seaweed Ulva prolifera has caused the world's largest green tide in the Yellow Sea, China. It has subsequently attracted considerable research interest. However, species identification is an essential step for advancing this research. Based on phylogenetic analyses using molecular sequences such as internal transcribed spacer (ITS) or ribulose bisphosphate carboxylase large chain (rbcL), specimens of U. prolifera collected worldwide were separated into a European clade and the Ulva linza-procera-prolifera (LPP) complex clade that included the Chinese bloom-forming strains and Japanese brackish strains. This has resulted in considerable controversy as to the identity of U. prolifera and the bloom-forming species in the Yellow Sea. To resolve this issue, we examined populations of U. prolifera from the type locality at Lolland Island, Denmark, and globally significant sites including sites from Japan and China using morphological, developmental, molecular and crossing studies. We found that almost all the Danish strains agree with the description of the type specimen and were included in the LPP clade. They had a branched morphology in culture and an obligate asexual life history with quadriflagellate zoosporoids. We conclude that this taxon in the LPP clade is true U. prolifera. Based on culture morphology, mating compatibility and the 5S rDNA spacer sequences, the Chinese bloom-forming strains were distinct, and the new subspecies U. prolifera subsp. qingdaoensis subsp. nov. is described. Strains of the European clade showing gamete incompatibility with the sexual members of the LPP clade were assigned to the species Ulva splitiana.
  • Tomokazu Yamazaki, Kensuke Ichihara, Ryogo Suzuki, Kenshiro Oshima, Shinichi Miyamura, Kazuyoshi Kuwano, Atsushi Toyoda, Yutaka Suzuki, Sumio Sugano, Masahira Hattori, Shigeyuki Kawano
    SCIENTIFIC REPORTS 7 2017年09月 [査読有り][通常論文]
     
    The evolution of sex chromosomes and mating loci in organisms with UV systems of sex/mating type determination in haploid phases via genes on UV chromosomes is not well understood. We report the structure of the mating type (MT) locus and its evolutionary history in the green seaweed Ulva partita, which is a multicellular organism with an isomorphic haploid-diploid life cycle and mating type determination in the haploid phase. Comprehensive comparison of a total of 12.0 and 16.6 Gb of genomic next-generation sequencing data for mt(-) and mt(+) strains identified highly rearranged MT loci of 1.0 and 1.5 Mb in size and containing 46 and 67 genes, respectively, including 23 gametologs. Molecular evolutionary analyses suggested that the MT loci diverged over a prolonged period in the individual mating types after their establishment in an ancestor. A gene encoding an RWP-RK domain-containing protein was found in the mt(-) MT locus but was not an ortholog of the chlorophycean mating type determination gene MID. Taken together, our results suggest that the genomic structure and its evolutionary history in the U. partita MT locus are similar to those on other UV chromosomes and that the MT locus genes are quite different from those of Chlorophyceae.
  • Masanori Hiraoka, Kensuke Ichihara, Wenrong Zhu, Satoshi Shimada, Naohiro Oka, Jianjun Cui, Shuntaro Tsubaki, Peimin He
    PHYCOLOGIA 56 5 517 - 532 2017年 [査読有り][通常論文]
     
    Phylogenetic clades based on DNA sequence data are heavily used to delimit species in the current taxonomy of Ulva. However, because hybridisation within clades and among other clades for other species has been seldom tested, it remains unclear if molecular clades agree with species boundaries based on the biological species concept. An ITS-based Ulva clade including many specimens collected worldwide was provisionally named 'U. flexuosa'; its species boundary is ambiguous, and in the literature this group has been variously merged with the closely related U. californica clade. In the present study, we clarified the species boundary of this clade and its taxonomic status. Namely reproductive relationships among strains in this and closely related clades were examined by culturing and hybridisation. The culture experiment demonstrated that the ITS-based clade includes a sexual variant and an obligate asexual variant. The sexual strains having 0%-0.4% divergence in ITS2 sequence successfully crossed with each other. In combinations among the closely related clades including true U. flexuosa with. > 1.2% distance in the sequence, no hybridisation occurred. With U. californica strains having a 1.2% sequence divergence, the provisional 'U. flexuosa' strains had few hybrid sporophytes, and these produced zoids that failed to develop normally. Based on these observations of prezygotic and postzygotic isolation, we conclude that the ITS-based clade delimits a different species from U. flexuosa and U. californica. Taxonomically, both the sexual and the asexual variants are assigned to U. mediterranea.
  • A. A. Saber, K. Ichihara, M. Cantonati
    PLANT BIOSYSTEMS 151 5 800 - 812 2017年 [査読有り][通常論文]
     
    Two Rhizoclonium strains thriving in contrasting spring types (slightly hot spring/ambient, shaded pool spring) and biogeographic areas (El-Farafra Oasis in the Western Desert of Egypt/River-Po Plain in Northern Italy) were studied in depth based on field and cultured material, bright-field and fluorescence microscopy, and phylogenetic molecular analyses (SSU and LSU rRNA gene sequences). This polyphasic approach revealed that the two Rh. strains clearly belonged to the Rhizoclonium clade but differed in some of their key diagnostic features. The Egyptian Rhizoclonium strain, isolated from the spring-fed (Ain El-Balad) agricultural ditch in El-Farafra Oasis, was described with the working name Rhizoclonium sp. 10.6m from a desert, slightly-hot spring' based on its smaller cell diameter, ecological and phylogenetic molecular traits compared to allied morphospecies. Moreover, it was highlighted that the L/D ratio can be more than 3.0 within this group. The Italian Rhizoclonium strain, collected from the Fontanile Valle Re-shaded, pool ambient spring (Emilia-Romagna Region), was virtually identical to other strains identified as Rh. hieroglyphicum from China and Japan, due to its highly supported congruence in morphological characteristics and phylogenetic position. This study provided the first partial LSU and SSU rRNA gene sequences for European Rh. hieroglyphicum based on available literature. Phenotypic plasticity of rhizoid formation was also observed in both Rhizoclonium strains studied using culturing approaching techniques. Our investigation also confirms that a lot of work with a variety of approaches is still needed to assess the ecological preferences, morphological plasticity, and phylogenetics of freshwater Rhizoclonium taxa worldwide.
  • Kensuke Ichihara, Satoshi Shimada, Kazuyuki Miyaji
    PHYTOTAXA 266 4 231 - 249 2016年06月 [査読有り][通常論文]
     
    Microfilamentous unbranched cladophoralean algae are distributed from high latitudes to the tropics in waters of varying salinities. Their simple morphology provides few diagnostic characteristics for distinguishing species, such that the taxonomic status of minute Cladophoraceae remains unclear. In a recent field survey in Japanese mangrove forests and brackish waters, we found Rhizoclonium-like cladophoralean algae (Cladophoraceae spp. 1-3). In molecular phylogenetic analyses based on partial small subunit ribosomal RNA (SSU) and large subunit ribosomal RNA (LSU) genes, these algae clustered with R. africanum Kutzing in the LSU tree and were separated from the true Rhizoclonium clade in both the LSU and SSU trees. An early divergence in the Cladophoraceae lineage was also strongly supported in both trees. Cladophoraceae spp. 1-3 and R. africanum shared a specific rhizoidal developmental structure, the "knee-like joint." Cladophoraceae spp. 1-3 also shared polypyramidal pyrenoids, while typical bilenticular pyrenoids are hardly found. Cladophoraceae sp. 1 is characterized by wider cells and more nuclei per cell than described taxa. Cladophoraceae sp. 3 had a smaller cell length/diameter ratio and fewer nuclei per cell than described taxa. Based on these distinct morphological features, we describe two new species: R. fractum Ichihara et Miyaji sp. nov. and R. umbraticum Ichihara et Miyaji sp. nov. We also revealed that Cladophoraceae sp. 2 should be assigned to the described species R. minutissimum (Zeller) P. C. Silva based on morphological characteristics.
  • Candidate key genes for low-salinity adaptation identified by RNA-seq comparison between closely related Ulva species in marine and brackish waters.
    Yuka Masakiyo, Atsushi Ogura, Kensuke Ichihara, Kei Yura, Satoshi Shimada
    Algal Resources 9: 61-76. 2016年 [査読有り][通常論文]
  • Satoshi Shimada, Kensuke Ichihara, Yuka Masakiyo, Riko Kawaguchi, Norio Kikuchi
    Seaweed Phylogeography: Adaptation and Evolution of Seaweeds under Environmental Change 345 - 360 2016年01月01日 [査読無し][通常論文]
     
    Comparative studies of closely related species or populations in contrasting environments can potentially provide insights into adaptive mechanisms. We reviewthe phylogeography and population diversity of brackish water species derived from marine species, Ulva prolifera Müller (Ulvophyceae) and Pyropia tenera (Kjellman) N. Kikuchi, M. Miyata, M.S. Hwang & H.G. Choi (Bangiophyceae). Brackish U. prolifera and marine Ulva linza L. have been resolved as closely related species based on phylogenetic analysis of moleclar markers, with U. linza apparently parental to U. prolifera. Our analyses of 5S rDNA spacer region in samples from an Ulvalean bloom in Qingdao, China, indicate that the species appear to be derived from Japanese U. prolifera. Hybridization tests suggest that U. linza and the Qingdao bloom samples are probably distinct species, but gene flow is possible between them. The threatened brackish water species, P. tenera, is morphologically and phylogenetically related to the coastal species, Pyropia yezoensis (Ueda) M.S. Hwang & H.G. Choi. One form, P. yezoensis Ueda f. narawaensis Miura (new combination "Pyropia yezoensis f. narawaensis" has not yet been proposed), is the largest aquaculture source of "Nori" in Japan. Hybridization between these species has been reported, especially between male P. tenera and female P. yezoensis. Sequences of the nrITS1 region and rbcL gene, and PCR-RFLP (ARP4 gene) analyses suggested that P. tenera is distributed across 15 prefectures from Kyushu to Tohoku in Japan but is restricted to estuarine and brackish water habitats. Based on SSR analysis on the genetically identified P. tenera samples, we conclude that this species spread from Kyushu to Tohoku through the Kanto region.
  • Kensuke Ichihara, Ryogo Suzuki, Tomokazu Yamazaki, Shuhei Ota, Yuko Mogi, Yayoi Kagami, Kazuyoshi Kuwano, Shigeyuki Kawano
    CYTOLOGIA 80 3 261 - 270 2015年09月 [査読無し][通常論文]
     
    In this report, Ulva partita Ichihara, sp. nov. (Ulvales, Ulvophyceae) was described from Japanese seashores. This species was characterized by (i) frequent branches in the basal region, but not in the middle to upper region, (ii) being up to 20 cm in height and 5mm in diameter, and (iii) containing chloroplasts covering the outer cell wall in the middle and upper regions of thalli, but with many chloroplasts leaning to one side of the cells in the basal region. Ulva partita is distinguished from morphologically similar species based on the branching pattern, early development pattern, and gamete size. Molecular phylogenetic analyses of nuclear-encoded ITS2 sequence and chloroplast-encoded rbcL sequences also strongly supported the independence of this species.
  • Kaoru Matsumoto, Kensuke Ichihara, Satoshi Shimada
    PHYCOLOGIA 53 2 127 - 136 2014年 [査読無し][通常論文]
     
    We conducted a phylogenetic and morphological reinvestigation of Petalonia species from the Pacific coast southeast of Honshu, Japan. Phylogenetic analyses based on plastid rbcL and the nuclear ITS regions resulted in three genetically distinct species: P. binghamiae, P. fascia, and Petalonia sp. Petalonia sp. was characterized by the medullary structure showing intermediate characteristics between those of P. binghamiae and P. fascia as well as by the thinner thallus. In addition, the habitat and the seasonality of Petalonia sp. were slightly different from those of the two species. Sexual fusion of plurizoids was observed on Petalonia sp., and the morphology of the prostrate sporophytes agreed with the previous reports of P. binghamiae and P. fascia. According to the characteristics, Petalonia sp. is described as a new species, P. tenuis sp. nov.
  • Kensuke Ichihara, Satoshi Shimada, Kazuyuki Miyaji
    Phycologia 52 5 398 - 410 2013年09月 [査読無し][通常論文]
     
    Analyses of partial small subunit (SSU) and large subunit (LSU) rRNA genes of Rhizoclonium-like filamentous green algae, collected from brackish waters in Japan, revealed the existence of five genetically distinct species. Four species (Rhizoclonium spp. 1-4) were closely related to Rhizoclonium hieroglyphicum. The phylogenetic position of the Rhizoclonium-like sp. 5 remained largely unresolved, although LSU analyses suggested a relationship with Chaetomorpha ligustica. Rhizoclonium spp. 1 and 4 were identified as Rhizoclonium riparium and Rhizoclonium lubricum, respectively. Rhizoclonium spp. 2 and 3 were morphologically distinguishable from other Rhizoclonium species and minute Chaetomorpha species. Rhizoclonium sp. 2 exhibited a characteristically small L/D (cell length/cell diameter) ratio and large number of nuclei (3-7 per cell), while Rhizoclonium sp. 3 was characterized by unique spindle or band-like, densely arranged chloroplasts therefore, we described them as new species, Rhizoclonium breve and Rhizoclonium confertum. Rhizoclonium-like sp. 5 was characterized by perforated chloroplasts and polypyramidal pyrenoids and was clearly distinct from known Rhizoclonium or Chaetomorpha species. Based on the phylogenetic position and morphological features of Rhizoclonium-like sp. 5, we described it as a new species of Chaetomorpha, Chaetomorpha tokyoensis.
  • Kensuke Ichihara, Kazuyuki Miyaji, Satoshi Shimada
    PHYCOLOGICAL RESEARCH 61 1 52 - 57 2013年01月 [査読無し][通常論文]
     
    The green macroalgal genus Ulva (Ulvales, Ulvophyceae, Chlorophyta) is distributed worldwide from marine to freshwater environments. Comparative analyses of hyposalinity tolerance among marine, brackish, and freshwater Ulva species were performed by fluorescein diacetate viability counts. The subtidal marine species Ulva sp., collected from a depth of 30m, showed the poorest tolerance to low salinity. This species died in 5 practical salinity units (PSU) artificial seawater or freshwater within 1 day. Its closely related species U. linza L. (an intertidal species) and U. prolifera Muller (a brackish species) showed varying tolerances to low salinity. After 7 days of freshwater exposure, the viability of U. linza L. decreased to approximately 20%, while U. prolifera Muller showed nearly 100% viability. The freshwater species U. limnetica Ichihara et Shimada, not yet found in coastal areas, was highly viable in seawater.
  • Morphological variations of the seagrass species, Halophila nipponica (Hydrocharitaceae, Alismatales)
    Satoshi Shimada, Maki Watanabe, Kensuke Ichihara, Masayuki Uchimura
    Coastal Marine Science 35 85 - 90 2012年 [査読有り][通常論文]
  • Threatened species Nemalionopsis tortuosa (Thoreales, Rhodophyta) in Japan, new locality and current condition of its all reported habitats.
    Satoshi Shimada, Kensuke Ichihara, Yuka Masakiyo, Masafumi Iima, Tadao Yoshida, Shigeru Kumano
    Algal resource 5 9 - 15 2012年 [査読有り][通常論文]
  • Kensuke Ichihara, Frederic Mineur, Satoshi Shimada
    JOURNAL OF PHYCOLOGY 47 3 584 - 590 2011年06月 [査読無し][通常論文]
     
    The macroalga Ulva limnetica K. Ichihara et S. Shimada is the only known Ulva species to be distributed exclusively in freshwater and is restricted to freshwater bodies in the Ryuku archipelago. Molecular phylogenetic analysis suggests that U. limnetica originally evolved from marine forms of Viva. The mechanisms of adaptation to freshwater in Ulva spp. are poorly understood. In this study, we isolated genes potentially involved in adaptation or tolerance to freshwater conditions in U. limnetica, using suppression subtractive hybridization between mRNAs of samples cultured in freshwater and seawater conditions. A total of 219 genes, up-regulated by the exposure of the macroalga to freshwater, were isolated. Reverse transcription-PCR (RT-PCR) revealed 39 clones, including malate dehydrogenase, soluble starch synthase, triosephosphate isomerase, plastid ribosomal protein, DnaJ-like protein, and chloroplast ascorbate peroxidase (APX), which were specifically or preferentially expressed in freshwater conditions. These 39 clones were also analyzed for their temporal transcriptional response to freshwater conditions. A large majority of these up-regulated genes showed a transient peak of expression after 1-4 h, followed in the next 24 h by a decrease to a stable level (over the 7 d of the experiment). After the initial response peak, the level of expression either remained higher than in the control (long-term response) or returned to a level similar to pretreatment level. A few genes showed a more delayed response (i.e., after several days) to freshwater exposure. Finally, we discussed the possible contributions of the freshwater-induced genes in the acquisition of freshwater adaptation or tolerance of U. limnetica.
  • Masanori Hiraoka, Kensuke Ichihara, Wenrong Zhu, Jiahai Ma, Satoshi Shimada
    PLOS ONE 6 5 2011年05月 [査読無し][通常論文]
     
    In the summer of 2008, immediately prior to the Beijing Olympics, a massive green tide of the genus Ulva covered the Qingdao coast of the Yellow Sea in China. Based on molecular analyses using the nuclear encoded rDNA internal transcribed spacer (ITS) region, the Qingdao strains dominating the green tide were reported to be included in a single phylogenetic clade, currently regarded as a single species. On the other hand, our detailed phylogenetic analyses of the clade, using a higher resolution DNA marker, suggested that two genetically separate entities could be included within the clade. However, speciation within the Ulva clade has not yet been examined. We examined the occurrence of an intricate speciation within the clade, including the Qingdao strains, via combined studies of culture, hybridization and phylogenetic analysis. The two entities separated by our phylogenetic analyses of the clade were simply distinguished as U. linza and U. prolifera morphologically by the absence or presence of branches in cultured thalli. The inclusion of sexual strains and several asexual strains were found in each taxon. Hybridizations among the sexual strains also supported the separation by a partial gamete incompatibility. The sexually reproducing Qingdao strains crossed with U. prolifera without any reproductive boundary, but a complete reproductive isolation to U. linza occurred by gamete incompatibility. The results demonstrate that the U. prolifera group includes two types of sexual strains distinguishable by crossing affinity to U. linza. Species identification within the Ulva clade requires high resolution DNA markers and/or hybridization experiments and is not possible by reliance on the ITS markers alone.
  • Enteromorpha-like Ulva (Ulvophyceae, Chlorophyta) Growing in the Todoroki River, Ishigaki Island, Japan, with Special Reference to Ulva meridionalis Hoiromoto et Shimada, sp. nov.
    Rika Horimoto, Yuka Masakiyo, Kensuke Ichihara, Satoshi Shimada
    Bull. Natl. Mus. Nat. Sci., Ser. B. 37 4 155 - 167 2011年 [査読有り][通常論文]
  • Phylogeographic analysis of the genus Ulva (Ulvales, Chlorophyta), including bloom sample in Qingdao, China
    Satoshi Shimada, Moe Nagano, Masanori Hiraoka, Kensuke Ichihara, Frederic Mineur, Wenrong Zhu
    Coastal Marine Science 34 1 117 - 122 2010年 [査読有り][通常論文]
  • Kensuke Ichihara, Shogo Arai, Masayuki Uchimura, Etienne J. Fay, Hiroki Ebata, Masanori Hiraoka, Satoshi Shimada
    PHYCOLOGICAL RESEARCH 57 2 94 - 103 2009年06月 [査読無し][通常論文]
     
    Ulva limnetica Ichihara et Shimada, sp. nov. (Ulvales, Ulvophyceae) is described from the Ryukyu Islands, Japan, and is characterized by thalli that are: (i) branched, tubular, fragile and wrinkled; (ii) up to 80 cm in height and up to 2 cm in diameter; (iii) light to yellowish green in color; and (iv) having an asexual reproduction by means of quadriflagellate swarmers. Rhizoidal cells bear tubular extensions on the outside of the cell layer in the stipe. Ulva limnetica is distinguished from species with similar thalli by chloroplast disposition, branching pattern, number of pyrenoids per cell and gross morphology. It is also distinguished by sequences of the nuclear-encoded 18S ribosomal RNA gene, internal transcribed spacer 2 region and the plastid-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxgenase gene (rbcL). Ulva limnetica was clustered with other Ulva species in an early diverging lineage within the genus.
  • Kensuke Ichihara, Shogo Arai, Satoshi Shimada
    PHYCOLOGICAL RESEARCH 57 2 104 - 110 2009年06月 [査読無し][通常論文]
     
    The macroalgal species Ulva limnetica Ichihara et Shimada was investigated to understand the molecular mechanism of its tolerance or adaptation to freshwater. We detected a 19 kDa protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which accumulated in greater amounts in freshwater conditions compared with marine conditions. The band was excised and the partial amino acid sequence was determined by Edoman degradation. Based on the sequences, we isolated the corresponding cDNA by the rapid amplification of cDNA ends (RACE) technique. The constructed, full-length cDNA was 1272 bp in length, consisting of 198 bp 5'-non-coding region, an open reading frame of 840 bp (279 amino acids), 233 bp 3'-non-coding region and poly (A) tail. The protein encoded by the cDNA showed 30% identity and 45% similarity to lectin isolated from Ulva pertusa Kjellman, and we named this gene ULL (encoding Ulva limnetica lectin-like protein). Northern blot analysis demonstrated that the expression level of the ULL in the freshwater-cultured sample was higher than in the seawater-cultured sample.
  • cDNA cloning of a lectin related gene in freshwater macroalga, Ulva limnetica (Ulvales, Ulvophyceae), preferentially expressed in freshwater than seawater conditions.
    Kensuke Ichihara, Shogo Arai, Satoshi Shimada
    Phycological Research 57: 104-110. 2009年 [査読有り][通常論文]

書籍

講演・口頭発表等

その他活動・業績

受賞

  • 2014年03月 日本藻類学会 第10回日本藻類学会研究奨励賞
     
    受賞者: 市原健介

共同研究・競争的資金等の研究課題

  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2021年04月 -2024年03月 
    代表者 : 市原 健介
  • 日本学術振興会:科学研究費助成事業 若手研究
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 市原 健介
     
    有性生殖は真核生物を特徴付ける重要な形質であり、動植物を問わずに進化してきた。動物では配偶子は大きく二形化し、精子と卵による卵生殖がおこなわれる。一方で、植物、特に藻類では同形から異形配偶子接合、卵生殖に至るまで進化の過程の様々なタイプの有性生殖が保存されている。アオサ藻綱に属するスジアオノリはわずかに大きさの異なる異形配偶子接合をおこなう。雌雄の配偶子を混合すると、配偶子は凝集し、鞭毛の先でお互いの性や種を「認識」し、同種の異性であることがわかると瞬時に細胞の「融合」が進む。またスジアオノリには光学顕微鏡下では配偶子と構造的な違いはほとんど見られないが、電子顕微鏡下では雌雄の配偶子に存在している接合装置が欠けた無性型二本鞭毛遊走子を放出する無性個体も存在する。雌雄配偶子および、この無性型二本鞭毛遊走子を微細構造とタンパク質レベルで比較することで、種と性の「認識」と細胞の「融合」という有性生殖の根幹を明らかにしたい。 当該年度は主に配偶子、二本鞭毛性遊走子から鞭毛を単離し、LC-MS/MS によるショットガン分析をおこなった。Fu et al. 2014.の手法を参考に、EGTAの濃度を調整することでスジアオノリの鞭毛を配偶子から単離する手法を開発した。雌雄配偶子および二本鞭毛性遊走子から単離した鞭毛をプロテオーム解析したところ、全体で251個のタンパク質を同定することができた。このうち80個は雌雄配偶子および二本鞭毛性遊走子で共通性がみられた。この中には鞭毛構成タンパク質が多く含まれていたが、解糖系に関わる酵素も同様に含まれており、アオサ藻綱の鞭毛運動は解糖系からのエネルギーが利用されている可能性が示唆された。
  • 日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 市原 健介
     
    1) 四万十川採集個体でのRAD-seq解析 昨年度に四万十川で採集し、SNPやマイクロサテライト部位などのゲノム中の多型情報を得るために、RAD-seq解析をおこなった。 2) スジアオノリの配偶子および2本鞭毛型、4本鞭毛型無性胞子のRNA-seq解析 スジアオノリの両接合型の配偶子、および2本鞭毛型無性胞子(無性配偶子)、4本鞭毛型無性胞子(無性胞子)を生殖細胞誘導によって、回収し、これらの細胞で発現している遺伝子の比較をおこなうためにRNA-seq解析をおこなった。真核生物における減数分裂コア遺伝子が保存されていることがわかり、このうち姉妹染色分体の結合に機能しているコヒーシン関連遺伝子(SYN3)が無性胞子や無性配偶子で発現量が低くなっており、前年度に観察された無性個体の生殖細胞形成時の第一減数分裂時に姉妹染色分体が乖離する現象と一致しているように思われた。 3) スジアオノリとヒラアオノリの全ゲノム解析 スジアオノリのゲノム解析を進め、現在までにドラフトゲノムの状態ではあるが、オスのゲノムサイズが約70 Mbpで遺伝子数は8,244個であることがわかっている。近縁種ヒラアオノリとスジアオノリのゲノムを比較したところ、ゲノム全体ではシンテニーが高度に保存されていることが確認できたが、性染色体領域ではシンテニーが失われており、この領域では遺伝子の転座等が起こりやすく、進化速度が速い領域であることが示唆された。またヒラアオノリで単離された性特異的な領域の遺伝子の多くは,スジアオノリにおいても,特定のスカッホールドにクラスター化して存在していることが明らかとなり,この性特異的な染色体領域はアオノリの性決定に保存的に機能していると考えられた。
  • 海藻の『淡水』・『汽水』への適応に関する分子進化学的研究
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2008年 -2010年 
    代表者 : 市原 健介
     
    本研究はアオサ属における海水域から汽水・淡水域への適応進化の分子機構を総合的に理解することを最終的な目標としている。実験は沖縄県で発見したアオサ属に含まれる唯一の淡水産種であるUlva limneticaを用いている。これまでの実験で本種は淡水・海水両条件で良好な生育を示すことが確認できている。 今年度は前年度に単離した淡水誘導性遺伝子群についてRT-PCRを用い、淡水環境での発現上昇の確認と淡水移行後の継時的な発現量の推移(1、4、24時間、3日、7日後)について解析を行った。cDNAサブトラクション法によって単離した217個の異なる淡水誘導性遺伝子のうち39個の遺伝子に関してRT-PCRを用いて淡水条件下で発現が上昇していることを確認した。またこれらの遺伝子についてその発現量の推移を解析した。その結果、39個の遺伝子群には発現上昇のパターンが異なる3つのグループが存在することが明らかになった。一つ目のグループは淡水移行直後の短い期間(1~12時間後)にのみ発現が上昇し、その後海水条件と同じ程度の発現量まで減少した。2つ目のグループでは淡水移行後に見られた発現の上昇が7日目まで維持された。また、3つ目のグループでは1つ目のグループと似た発現パターンを示したが、発現量のピークはより遅い3、7日目に見られた。2つ目のグループは急激なイオン・浸透圧の変化に対するストレス応答など、1,3つ目のグループは淡水環境に藻体を順応させ、維持していくために必要な遺伝子群がそれぞれ含まれているのではないかと考えている。ここまでの部分は論文としてまとめJournal of Phycologyに受理されている。また、これらの遺伝子のうちアスコルビン酸ペルオキシダーゼ、トリオースリン酸イソメラーゼ、リボソームタンパク質などは汽水産種スジアオノリ、海産種ウスバアオノリ、アナアオサでオーソログの単離を行い、現在、それぞれの低塩濃度条件での発現量の推移をrealtime-PCRによって調査している。

教育活動情報

主要な担当授業

  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    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
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    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

大学運営

委員歴

  • 2018年04月 - 現在   日本藻類学会   和文学会誌「藻類」編集委員


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