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

在分析在性腺发生中显示缺陷的突变体之前，构成性腺的细胞谱系已经在运动性、起源和翻译调节方面进行了表征。对突变体青鳉进行了表型分析和突变鉴定，结果表明，托托罗（tot）为性腺肥大的青鳉。表型分析表明，tot具有过多的生殖细胞和一半的遗传男性表现出男性到女性的性逆转。在抗苗勒管激素受体II型的激酶结构域中发现了突变，导致酪氨酸被半胱氨酸取代。已知该基因参与仅在哺乳动物中发现的附属器官的性别特异性发育，并且在其他脊椎动物中的功能仍有待阐明。我们的研究结果表明，该基因参与生殖细胞的增殖，在性别依赖的方式。由于推测性逆转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青鳉。生殖细胞缺陷型青鳉表现出雌雄逆转，表明生殖细胞在性腺发育过程中具有重要的两性异形性，并在其表面抗原基因中发现一个zenzai突变体。体内生殖细胞示踪分析表明，该突变体的生殖腺中存在两种增殖方式，参与生殖细胞维持的增殖过程受到影响，导致其在成虫期不育。

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.