Ph. D, Hokkaido University, Mar. 2013

Life Science, Developmental biology

Life Science, Animal physiological chemistry, physiology and behavioral biology

Life Science, Morphology and anatomical structure

Bachelor's degree program, School of Science

Master's degree program, Graduate School of Life Science

Doctoral (PhD) degree program, Graduate School of Life Science

Abnormal Sperm Morphology in Lodpr/lncRNA-HSVIII Knockout Mice with Advancing Age
Pummarin Tippramuan; Luo Yujia; Yui Satoh; Kazuhiro Kitada; Chika Fujimori; Atsushi P. Kimura
Reproductive Sciences, 30 Apr. 2026, [Peer-reviewed]
Scientific journal

The Bivalent Chromatin and a Potential Silencer for Differential Expression of PRSS Genes in the Human Testis
Kouta Iijima; Ryuzaburo Shibayama; Chika Fujimori; Atsushi P. Kimura
Molecular Reproduction and Development, Feb. 2026, [Peer-reviewed], [Corresponding author]
Scientific journal

Direct photoreception by pituitary endocrine cells regulates hormone release and pigmentation.
Ayaka Fukuda; Keita Sato; Chika Fujimori; Takahiro Yamashita; Atsuko Takeuchi; Hideyo Ohuchi; Chie Umatani; Shinji Kanda
Science (New York, N.Y.), 387, 6729, 43, 48, 03 Jan. 2025, [Peer-reviewed], [International Magazine]
English, Scientific journal, The recent discovery of nonvisual photoreceptors in various organs has raised expectations for uncovering their roles and underlying mechanisms. In this work, we identified a previously unrecognized hormone-releasing mechanism in the pituitary of the Japanese rice fish (medaka) induced by light. Ca2+ imaging analysis revealed that melanotrophs, a type of pituitary endocrine cell that secretes melanocyte-stimulating hormone, robustly increase the concentration of intracellular Ca2+ during short-wavelength light exposure. Moreover, we identified Opn5m as the key molecule that drives this response. Knocking out opn5m attenuated melanogenesis by reducing tyrosinase expression in the skin. Our findings suggest a mechanism in which direct reception of short-wavelength light by pituitary melanotrophs triggers a pathway that might contribute to protection from ultraviolet radiation in medaka.

Functional characterization of follicle-stimulating hormone and luteinizing hormone receptors in cloudy catshark, Scyliorhinus torazame
Shogo Arimura; Marty Kwok Shing Wong; Ryotaro Inoue; Mai Kawano; Koya Shimoyama; Chika Fujimori; Kotaro Tokunaga; Wataru Takagi; Susumu Hyodo
General and Comparative Endocrinology, 354, 01 Aug. 2024, [Peer-reviewed]
Scientific journal

Long-lasting redundant gnrh1/3 expression in GnRH neurons enabled apparent switching of paralog usage during evolution.
Chika Fujimori; Kohei Sugimoto; Mio Ishida; Christopher Yang; Daichi Kayo; Soma Tomihara; Kaori Sano; Yasuhisa Akazome; Yoshitaka Oka; Shinji Kanda
iScience, 27, 3, 109304, 109304, 15 Mar. 2024, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, Expressed subtype of paralogous genes in functionally homologous cells sometimes show differences across species, the reasons for which have not been explained. The present study examined hypophysiotropic gonadotropin-releasing hormone (GnRH) neurons in vertebrates to investigate this mechanism. These neurons express either gnrh1 or gnrh3 paralogs, depending on the species, and apparent switching of the expressed paralogs in them occurred at least four times in vertebrate evolution. First, we found redundant expression of gnrh1 and gnrh3 in a single neuron in piranha and hypothesized that it may represent an ancestral GnRH system. Moreover, the gnrh1/gnrh3 enhancer of piranha induced reporter RFP/GFP co-expression in a single hypophysiotropic GnRH neuron in both zebrafish and medaka, whose GnRH neurons only express either gnrh3 or gnrh1. Thus, we propose that redundant expression of gnrh1/3 of relatively recent common ancestors may be the key to apparent switching of the paralog usage among present-day species.

The PGE2/Ptger4b pathway regulates ovulation by inducing intracellular actin cytoskeleton rearrangement via the Rho/Rock pathway in the granulosa cells of periovulatory follicles in the teleost medaka.
Katsueki Ogiwara; Chika Fujimori; Takayuki Takahashi
Molecular and cellular endocrinology, 111816, 111816, 18 Nov. 2022, [Peer-reviewed], [International Magazine]
English, Scientific journal, We have previously shown that the prostaglandin E2/Ptger4b receptor system is involved in ovulation in teleost medaka and induces intracellular actin cytoskeleton rearrangement in the granulosa cells of preovulatory follicles. In this study, we investigated the signaling pathways through which prostaglandin E2 induces a change in the actin cytoskeleton. Treating preovulatory follicles with GW627368X (Ptger4b antagonist), a Rho inhibitor, or Y-27632 [Rho-associated protein kinase (Rock) inhibitor] inhibited not only in vitro follicle ovulation but also intracellular actin cytoskeleton rearrangement. Active Rhoa-c and Rock1 were detected in follicles immediately before ovulation. GW627368X also inhibited Rhoa-c activation and cytoskeleton rearrangement. PGE2-induced actin cytoskeleton rearrangement was not observed in the Ptger4b-, Rhoa-c-, or Rock1-deficient OLHNI-2 cells. These results indicate that the PGE2/Ptger4b pathway regulates intracellular actin cytoskeleton rearrangement via the Rho/Rock pathway in the granulosa cells of preovulatory follicles during medaka ovulation.

In vitro and in vivo gene transfer in the cloudy catshark Scyliorhinus torazame.
Chika Fujimori; Chie Umatani; Misaki Chimura; Shigeho Ijiri; Hisanori Bando; Susumu Hyodo; Shinji Kanda
Development, growth & differentiation, 14 Nov. 2022, [Peer-reviewed], [Lead author, Corresponding author], [Domestic magazines]
English, Scientific journal, Cartilaginous fishes have various unique physiological features such as cartilaginous skeletons and a urea-based osmoregulation strategy for adaptation to their marine environment. Also, because they are a sister group of bony vertebrates, understanding their unique features is important from an evolutionary perspective. However, genetic engineering, which can analyze gene functions as well as cellular behavior, has not been effectively utilized in cartilaginous fishes. This is partly because their reproductive strategy involves internal fertilization, which results in difficulty in microinjection into fertilized eggs at the early developmental stage. Here, to identify efficient gene transfer methods in cartilaginous fishes, we examined the effects of various methods both in vitro and in vivo using the cloudy catshark, a candidate model cartilaginous fish species. In all methods, green fluorescent protein (GFP) expression was used to evaluate exogenous gene transfer. First, we examined gene transfer to primary cultured cells from cloudy catshark embryos by lipofection, polyethylenimine (PEI), adenovirus, baculovirus and electroporation. Among the methods tested, lipofection, electroporation and baculovirus infection enabled the successful transfer of exogenous genes into primary cultured cells. We then attempted in vivo transfection into cloudy catshark embryos by electroporation and baculovirus infection. Although baculovirus-injected groups did not show GFP fluorescence, electroporation successfully introduced GFP into muscle cells. Furthermore, we succeeded in GFP transfer into adult tissues by electroporation. The in vitro and in vivo gene transfer methods that worked in this study may identify paths for future genetic manipulation including knockout experiments and cellular linage analysis in cartilaginous fishes.

Germ cells in the teleost fish medaka have an inherent feminizing effect
Toshiya Nishimura; Kazuki Yamada; Chika Fujimori; Mariko Kikuchi; Toshihiro Kawasaki; Kellee R. Siegfried; Noriyoshi Sakai; Minoru Tanaka
PLoS Genetics, 14, 3, e1007259, Public Library of Science, 01 Mar. 2018, [Peer-reviewed]
English, Scientific journal

Roles of proteases and prostaglandins in follicle rupture during ovulation in the medaka
T. Takahashi; C. Fujimori; A. Hagiwara; K. Ogiwara
PROCEEDINGS OF THE 17TH INTERNATIONAL CONGRESS OF COMPARATIVE ENDOCRINOLOGY (ICCE 2013), 23, 28, 2014, [Peer-reviewed]
English, International conference proceedings

Recent Advances in the Understanding of Teleost Medaka Ovulation: The Roles of Proteases and Prostaglandins
Takayuki Takahashi; Chika Fujimori; Akane Hagiwara; Katsueki Ogiwara
ZOOLOGICAL SCIENCE, 30, 4, 239, 247, Apr. 2013, [Peer-reviewed]
English

Characterization of Luteinizing Hormone and Luteinizing Hormone Receptor and Their Indispensable Role in the Ovulatory Process of the Medaka
Katsueki Ogiwara; Chika Fujimori; Sanath Rajapakse; Takayuki Takahashi
PLOS ONE, 8, 1, e54482, Jan. 2013, [Peer-reviewed]
English, Scientific journal

New evidence for the involvement of prostaglandin receptor EP4b in ovulation of the medaka, Oryzias latipes
Chika Fujimori; Katsueki Ogiwara; Akane Hagiwara; Takayuki Takahashi
MOLECULAR AND CELLULAR ENDOCRINOLOGY, 362, 1-2, 76, 84, Oct. 2012, [Peer-reviewed], [Lead author]
English, Scientific journal

Expression of cyclooxygenase-2 and prostaglandin receptor EP4b mRNA in the ovary of the medaka fish, Oryzias latipes: Possible involvement in ovulation
Chika Fujimori; Katsueki Ogiwara; Akane Hagiwara; Sanath Rajapakse; Atsushi Kimura; Takayuki Takahashi
MOLECULAR AND CELLULAR ENDOCRINOLOGY, 332, 1-2, 67, 77, Jan. 2011, [Peer-reviewed], [Lead author]
English, Scientific journal

Expression and localization of collagen type IV alpha 1 chain in medaka ovary
Yumiko Kato; Katsueki Ogiwara; Chika Fujimori; Atsushi Kimura; Takayuki Takahashi
CELL AND TISSUE RESEARCH, 340, 3, 595, 605, Jun. 2010, [Peer-reviewed]
English, Scientific journal

Collagen Type-1 alpha 1 Chain mRNA is Expressed in the Follicle Cells of the Medaka Ovary
Maya Horiguchi; Chika Fujimori; Katsueki Ogiwara; Akihiko Moriyama; Takayuki Takahashi
ZOOLOGICAL SCIENCE, 25, 9, 937, 945, Sep. 2008, [Peer-reviewed]
English, Scientific journal

Medaka as a model teleost: characteristics and approaches of genetic modification
Tokiro Ishikawa; Yu Murakami; Chika Fujimori; Masato Kinoshita; Kiyoshi Naruse; Shinji Kanda, Laboratory Fish in Biomedical Research, 185, 213, 2022
Elsevier

Laboratory Fish in Biomedical Research Biology, Husbandry and Research Applications for zebrafish, medaka, killifish, cavefish, stickleback, goldfish and Danionella translucida
Chapter 9 - Medaka as a model teleost: characteristics and approaches of genetic modification.
Academic Press, 2021, 9780128210994

生殖発生機構学特論, 2024年, 修士課程, 生命科学院

ISP生物科学実習Ⅱ・a, 2024年, 学士課程, 理学部

ISP生物科学実習Ⅱ・b, 2024年, 学士課程, 理学部

発生学実習, 2024年, 学士課程, 理学部

発生学実習, 2024年, 学士課程, 理学部

英語演習, 2024年, 学士課程, 全学教育

Apr. 2008 - Present
日本動物学会

Oct. 2007 - Present
日本比較内分泌学会

Functional changes of hormones which regulate reproduction during vertebrate evolution
Grants-in-Aid for Scientific Research
01 Apr. 2024 - 31 Mar. 2027
藤森 千加
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 24K09522

Introduction of reverse genetic analysis into cartilaginous fish research
Grants-in-Aid for Scientific Research
28 Jun. 2019 - 31 Mar. 2022
HYODO SUSUMU
In this study, we aimed to introduce reverse genetic analysis into the study of cartilaginous fish, which occupy an important position in the evolution of vertebrates and have various characteristics such as morphology, development, adaptation, and reproduction. First, we clarified the process of embryonic development including nutrient digestion and absorption function during the ontogeny of cloudy catshark, and also investigated endocrine regulation of the reproductive cycle of catshark from ovulation to fertilization, egg-case formation and spawning by ultrasound investigation and concomitant plasma hormone measurement. Based on these basic information, we established primary cultured cells from cloudy catshark embryos and optimized gene transfer using various methods. Furthermore, we conducted introduction of genes into the embryos of cloudy catsharks and the testes of adult fish, an exploratory research aiming at future reverse genetic study.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), The University of Tokyo, 19K22414

Elucidation of the process of duplicated gene independence using FSH and LH as a model.
Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists
Apr. 2019 - Mar. 2022
Fujimori Chika
The genes fshb and lhb, which produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are paralogous genes derived from the duplication of identical genes. They are co-expressed in the same pituitary cells in mammals, whereas they are expressed in separate cells in teleost fish. In this study, we investigated how the expression patterns of fshb and lhb changed during evolution by introducing the enhancer sequences of fshb and lhb from co-expressing and differentially expressing species into medaka and checking the reporter activity in the pituitary cells of medaka. Immunohistochemistry and in situ hybridization on the same sections revealed the correspondence between fshb/lhb co-expressing cells of co-expressing species and fshb- and lhb-expressing cells of differentially expressing species.
Japan Society for the Promotion of Science, Grant-in-Aid for Early-Career Scientists, The University of Tokyo, 19K16176

The role of AMH in gonadal size
Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
01 Apr. 2015 - 31 Mar. 2018
Fujimori Chika
In previous studies, anti-mullerian hormone (amh) signal deficient medaka hotei were isolated and they showed hyperactivation of germline stem cell division, resulting germ cell excess. I performed medaka ovarian cell culture and examined the character of cultured cells . After 14 days of cell culture, functional sperm were produced from cultured ovarian germ cells, suggesting that medaka adult ovaries have germ cells with potential to differentiate into both oocytes and sperm.
Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Principal investigator, Competitive research funding, 15K18572

プロスタグランジンによる脊椎動物に共通の排卵誘導機構の解明
特別研究員
01 Apr. 2010 - 31 Mar. 2013
藤森 千加
プロスタグランジン(PG)は、多くの脊椎動物において排卵誘導作用を示す因子として知られているが、その分子機構については未だに明らかになっていない。そこで、本研究では排卵研究に適した生物であるメダカを用いて、PGによる排卵誘導の分子機構を明らかにすることを目的とする。これまでにPG合成酵素COX-2及びPGE2受容体EP4bの解析を行い、PGE2が排卵時にアクチン重合調節に関与していることを示唆する結果を得た。平成24年度ではPGE2シグナルによって働くアクチン重合の調節機構及び排卵への作用機構について調査し、以下の研究成果が得られた。
1.アクチン重合を調節する因子であるRhoファミリーについて、メダカの排卵への関与をin vitro排卵実験系を用いて調査した。その結果、Rho阻害剤でのみ排卵が阻害された。さらに、Rhoの下流因子であるRhoキナーゼの阻害剤をin vitro排卵実験系に添加した場合においても排卵が阻害された。
2.メダカのゲノムデータベースより、Rho遺伝子はRhoA, RhoB, RhoCの3種類が存在しており、排卵前濾胞における各Rho遺伝子の発現量を調べた。その結果、RhoAが最も高く発現していた。また、排卵前濾胞において活性型RhoAが検出された。
3.メダカ排卵時における濾胞の収縮とPGE2の作用との関連について調査を行った。その結果、EP4bアンタゴニストによって濾胞の収縮が阻害された。また、EP4bアンタゴニストとRho活性化剤を添加し培養を行うと、何も添加していない場合と同程度まで収縮した。
以上の結果より、メダカではPGE2が、EP4b-RhoA-アクチン重合調節の経路を介し、濾胞を収縮させることによって、排卵に寄与していると予想された。
日本学術振興会, 特別研究員奨励費, 北海道大学, Principal investigator, Competitive research funding, 10J02188