Researcher Information



Studies of the mechanisms that assure the continuity and diversity of Life.

Department of Biological Sciences, Reproductive and Developmental Biology


Analyses of molecular and cellular mechanisms of gametogenesis and gamete matuation, using fish and frog as experimental models.

FieldReproductive Biology, Developmental Biology, Zoology, Cell Biology, Biochemistry, Molecular Biology
KeywordMedaka, Zebrafish, Oocyte, Sperm, Fertilization, Embryonic Development, Messenger RNA, Translational Control

Introduction of Research

The life of many multicellular organisms begins with the union (fertilization) of germ cells (the eggs and the spermatozoa). (See Figure: Germ cells responsible for the continuity and diversity of life.) The processes during which the spermatozoa and eggs are produced are called spermatogenesis and oogenesis, respectively. These processes are indispensable for organisms that use sexual reproduction to maintain the species beyond the limited life of individuals. In contrast to the somatic cells that compose and maintain the organisms, the germ cells function to extend life to the next generation. The eggs and spermatozoa are highly differentiated cells, but in some aspects they are undifferentiated cells that retain the ability to become various kinds of cells. The germ cells thus mysteriously have the properties of being both differentiated and undifferentiated, and with the aid of these cells, organisms can maintain the species.
In addition to the contribution of germ cells to the continuity of life, the recombination of genes during oogenesis and spermatogenesis and the blending of genes by fertilization give diversity to organisms. Consequently, the germ cells are responsible for both the continuity and the diversity of life. Investigations into the mechanisms by which the germ cells are produced and fertilized should lead to an understanding of the mechanisms that assure two major contradictory characteristics of life: being able to reproduce those equal to the self and to produce those different from the self.
Our laboratory was established in 1993 for studying gametogenesis, gamete maturation, and fertilization, using fish and amphibians as experimental animals. Our research effort in recent years concentrates on the following two subjects.
1 Molecular mechanisms of the formation, activation and function of maturation-promoting factor (MPF). (See Figures: Micrograph of the animal polar region of zebrafish oocyte and Molecular mechanisms of oocyte maturation.)
2 Molecular and cellular biological investigations on the mechanisms of spermatogenesis with a cell culture system. (See Figure: Medaka spermatogenesis in vitro.)
In our laboratory, we have been studying the formation and maturation of germ cells, using fishes (goldfish, loach, eel, medaka, and zebrafish), amphibians (toad, frog, and newt) and mammals (pig and mouse) as experimental models. (See Figure: Experimental animals.)
In addition, we are also involved in the field of fishery science, for the efficient collection of natural spats of Japanese scallop. (See Figure: Immunostaining of Japanese scallop larvae with a specific antibody.)

Germ cells responsible for the continuity and diversity of life.
Micrograph of the animal polar region of zebrafish oocyte. CA, coritcal alveolus, EC, egg chorion; GV, germinal vesicle (the oocyte nucleus); MP, micropyle (the spem entry site); YG, yolk granule.
Molecular mechanisms of oocyte maturation.
Medaka spermatogenesis in vitro.
Experimental animals.
Immunostaining of Japanese scallop larvae with a specific antibody. Only the scallop larvae are stained in deep purple.

Representative Achievements

Staufen1, Kinesin1 and microtubule function in cyclin B1 mRNA transport to the animal polar cytoplasm of zebrafish oocytes. K. Takahashi, K. Ishii, and M. Yamashita, Biochem. Biophys. Res. Commun., 2018, 503, 2778-2783.
Practical improvement of the immunostaining method used for investigating the distribution of Japanese scallop (Mizuhopecten yessoensis) larvae in the field, Y. Shimizu, T. Karino, M. Narita, S. Itakura, K. Enomoto, M. Toda, T. Kawasaki, S. Takabatake, T. Iwai and M. Yamashita, Scientific Reports of Hokkaido Fisheries Research Institutes, 2016, 89, 1-8 [In Japanese with English abstract].
Immunoreactive insulin in diabetes mellitus patientsera detected by ultrasensitive ELISA with thio-NAD cycling, E. Ito, M. Kaneda, H. Kodama, M. Morikawa, M. Tai, K. Aoki, S. Watabe, K. Nakaishi, S. Hashida, S. Tada, N. Kuroda, H. Imachi, K. Murao, M. Yamashita, T. Yoshimura and T. Miura, BioTechniques, 2015, 59, 359-367.
Real-time imaging of actin filaments in the zebrafish oocyte and embryo, Y. Nukada, M. Horie, A. Fukui, T. Kotani and M. Yamashita, Cytoskeleton, 2015, 72, 491-501.
Possible involvement of insulin-like growth factor 2 mRNA-binding protein 3 in zebrafish oocyte maturation as a novel cyclin B1 mRNA-binding protein that represses the translation in immature oocytes, K. Takahashi, T. Kotani, Y. Katsu and M. Yamashita, Biochem. Biophys. Res. Commun., 2014, 448, 22-27.

Related industries

Fishery Science, Medical Science, Pharmaceutical Science
Academic degreeDoctor of Science (Ph.D.)
Academic background1979 Bachelor of Science, School of Science, Hokkaido University
1981 Master of Science, Graduate School of Science, Hokkaido University
1984 Doctor of Science (Ph.D.), Graduate School of Science, Hokkaido University
1989 Assistant Professor, National Institute for Basic Biology, Okazaki
1993 Associate Professor, Faculty of Science, Hokkaido University
1998 Professor, Faculty of Science, Hokkaido University
Affiliated academic societyThe Japanese Society of Zoology
Room addressScience Buiding 5 5-1108