山下正兼 教授 / YAMASHITA, Masakane

生命の連続性と多様性の源を探る

山下正兼 教授 /  YAMASHITA, Masakane

研究分野・テーマ・内容

研究分野 生殖生物学
研究テーマ 生殖細胞(卵と精子)が作られる仕組みを探る

研究内容

生殖細胞を作り受精させることは、個体の限られた寿命を越え、種を永遠に存続させるために必須の過程です。これらの過程で起こる遺伝子の再編は、生物に多様性を与え、多種多様な種を生み出す原動力にもなっています。生殖細胞が作られる仕組みの解明は、人工受精、避妊、有用生物種の作出など、我々の生活に深く関係する種々の生殖操作にも直結します。
当研究室では、主に魚類と両生類を実験材料に、生殖細胞が作られ、成熟し、受精する仕組みを、分子や細胞のレベルで明らかにする研究を行っています。特に、減数分裂における遺伝子発現の翻訳レベルでの制御やタンパク質の機能解析に焦点を絞って研究を進めています。

メッセージ

生物がどのような仕組みで生命を連続させているのかを細胞や分子のレベルで調べてみたい方は、私たちと一緒に研究しましょう。生殖生物学は未知の事柄にあふれた発展途上の学問分野です。特に以下のような方を歓迎します。1)生殖現象(卵・精子・受精・発生など)に興味がある人、2)科学研究者になりたいと強く思っている人、3)理論よりも実験を好む人、4)結果を一刻も早く知りたいと思う人(今日できることは明日に延ばさない人)、5)教科書や論文に書かれている事柄でも、自分で確かめないと気が済まない人。研究内容の詳しい説明や実験室の見学等は随時実施します。上記のうち、一つでも該当する人はメールで御連絡ください。

参考文献・論文・著書

nameYAMASHITA Masakane

Research subject

Specialized field

Reproductive and Developmental Biology in Animals

Key words

・African clawed frog, Xenopus laevis
・Cell culture
・Chinese medaka, Oryzias curvinotus
・Gametogenesis and oocyte maturation in fish and frogs
・Intracellular localization and translational control of mRNA
・Japanese medaka, Oryzias latipes
・Javanese medaka, Oryzias hubbsi
・Transgenic fish
・Zebrafish, Danio rerio

Research subject

The life of many multicellular organisms begins with the union (fertilization) of germ cells (the eggs and the spermatozoa). The processes during which the spermatozoa and eggs are produced are called spermatogenesis and oogenesis, respectively, and called gametogenesis collectively. 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 of 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 four subjects: 1) Elucidation of the molecular mechanisms of oocyte maturation in zebrafish and African clawed frog, with particular attention to the translational activation of mRNAs stored in oocytes; 2) Molecular and cellular biological investigations of medaka spermatogenesis using a cell culture system that can recapitulate the whole spermatogenesis from spermatogonia to spermatozoa in vitro; 3) Development of a new technique for producing transgenic medaka by means of transgenic spermatozoa produced in vitro; and 4) Understanding of the control mechanisms of chromosomal behavior in mitosis and meiosis revealed by abnormalities occurring in interspecific medaka hybrids (Oryzias latipes-hubbsi and O. latipes-curvinotus).

図

message

We would like to collaborate with the following people: 1) those who are interested in reproductive phenomena including gametogenesis, gamete maturation, fertilization and embryonic development; 2) those who really want to be a scientist; 3) those who prefer experiments to theories; 4) those who want to find out the results of an experiment as soon as possible; and 5) those who are not satisfied unless confirming the truth of a matter by themselves.

references

  • Iwai, T., et al. (2011) Interspecific medaka hybrids as experimental models for investigating cell division and germ cell development. In Medaka: Model for Organogenesis, Human Diseases and Evolution (Naruse, K., et al. eds.), Chapter 19, pp. 287-303, Springer.
  • Ota, R., et al. (2011) Possible involvement of Nemo-like kinase 1 in Xenopusoocyte maturation as a kinase responsible for Pumilio1, Pumilio2, and CPEB phosphorylation. Biochemistry, 50, 5648–5659.
  • Ota, R., et al. (2011) Biochemical characterization of Pumilio1 and Pumilio2 inXenopus oocytes. J. Biol. Chem., 286, 2853-2863.
  • Yasuda, K., et al. (2010) Transgenic zebrafish reveals novel mechanisms of translational control of cyclin B1 mRNA in oocytes. Dev. Biol., 348, 76-86.
  • Kotani, T., et al. (2010) Mys protein regulates protein kinase A activity by interacting with regulatory type I subunit during vertebrate development. J. Biol. Chem., 285, 5106-5116.
  • Iwai, T., et al. (2009) Production of transgenic medaka fish carrying fluorescent nuclei and chromosomes. Zool. Sci., 26, 9-16.
  • Otani, S., et al. (2009) Artificial fertilization by intracytoplasmic sperm injection (ICSI) in a teleost fish, the medaka Oryzias latipesBiol. Reprod., 80, 175-183.