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研究発表を行った学会；
・8th International Symposium on Reproductive Physiology in fish.
　2007年6月 3日~ 8日(フランス)

タイトル；Role of Mullerian inhibiting substance on gonadal sex differentiation in medaka (Oryzias latipes).
　
発表者；　白石　絵吏　氏
　　　（熊本大学　大学院自然科学研究科　理学専攻生命科学講座）
Abstract；
BACKGROUND: First appearance of morphological sex differentiation in medaka is that the genetic female (XX) acquires more number of germ cells than the genetic male (XY) by the hatching stage. Mullerian inhibiting substance (MIS), also known as anti-Mullerian hormone, is a glycoprotein belonging to transforming growth factor β superfamily. In mammals, MIS is responsible for regression of Mullerian ducts, anlagen of the female reproductive ducts, in the male fetus. However, the role of MIS in gonadal sex differentiation of teleost fishes, which do not have the Mullerian ducts, has yet to be clarified.
To elucidate the role of MIS on gonadal sex differentiation in medaka (Oryzias latipes), which is a small laboratory fish with several advantages such as a short generation time, small genome size, and also several useful strains, we performed expression and functional analyses of MIS during the sex differentiation in medaka.

METHODS: We first isolated a MIS cDNA from medaka testes and examined the expression pattern of MIS mRNA in gonads of both sexes during sex differentiation period by in situ hybridization. Next, we performed loss-of-function experiment of MIS by injecting MIS antisense oligo (MIS-AS) into fertilized eggs of the olvas-GFP transgenic medaka line, which allows us to monitor germ cells by GFP fluorescence.

RESULTS: MIS mRNA was expressed specifically in the somatic cells surrounding the germ cells of both sexes during the sex differentiation. In loss-of-function experiment of MIS, before primordial germ cells reach the gonadal region, there were no significant differences in the number of GFP-positive germ cells of both sexes in MIS-AS-injected embryos compared to the controls. After the sex differentiation, there were a small numbers of the germ cells of both sexes in MIS-AS-injected embryos as compared to controls.

CONCLUSION: Loss-of-function of MIS resulted in suppression of germ cell proliferation in both sexes during the sex differentiation, indicating that MIS is required for germ cell proliferation during early gonadal sex differentiation in medaka.