Phenotypic Analyses and Identification of Causal Mutations In Medaka Mutants with Gonadal Dysgenesis.

在分析性腺发生缺陷的突变体之前，构成性腺的细胞系已经在运动、起源和翻译调控方面进行了表征。然后，对突变体medaka进行了表型分析和突变鉴定。突变medaka龙猫（totoro）被鉴定为性腺肥大的medaka。表型分析表明，tot具有过多的生殖细胞，一半的遗传雄性表现出雄性向雌性的性别逆转。在抗苗勒管激素受体II型的激酶结构域发现突变，导致酪氨酸向半胱氨酸取代。该基因仅在哺乳动物中发现，与辅助器官的性别特异性发育有关，而在其他脊椎动物中的功能仍有待阐明。我们的结果表明，该基因以性别依赖的方式参与生殖细胞的增殖。由于性别逆转被推测是由于生殖细胞数量激增的结果，因此产生了生殖细胞完全丧失的medaka。生殖细胞缺陷的medaka表现出雌性-雄性的性别逆转，表明生殖细胞深深致力于两性二形性腺激素的产生。在一个表面抗原基因中也发现了zenzai突变体的突变。体内生殖细胞示踪分析表明，该突变体在生殖腺中存在两种类型的增殖，参与生殖细胞维持的增殖过程受到影响，导致成年期不育。

Before analysis of the mutants displaying defects in gonadogenesis, the cell lineages that constitute the gonad have been characterized in terms of the motility, origin and translational regulation. Then, phenotypic analyses and identification of the mutations have been performed for the mutant medaka.Mutant medaka, totoro (tot), was identified as medaka showing a hypertrophic gonad. Phenotypic analyses showed that tot possessed an excessive number of germ cells and a half of genetic male exhibited male-to-female sex reversal. A mutation was found in the kinase domain of anti-Mullerian hormone receptor type II, resulting in tyrosine to cysteine substitution. This gene has been known to be involved in sex-specific development of accessory organs found in only mammals and function in other vertebrates remained to be elucidated. Our result indicated that this gene is involved in proliferation of germ cells in a sex-dependent manner. Since sex-reversal was speculated to be due to a result of a burst number of germ cells, medaka with the complete loss of germ cells were generated. The germ-cell deficient medaka displayed a female-male sex reversal, suggesting that germ cells are deeply committed to sexual dimorphic gonadogenesis.A mutation of zenzai mutant has also been identified in one of the surface antigen genes. In vivo germ cell-tracing analysis indicated that two types of proliferation are present in the gonads and the process of proliferation involved in germ cell maintenance was affected in this mutant, which brings about sterility in adult stage.