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¥3,700,000 (Direct Cost : ¥3,700,000)
Fiscal Year 2005 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 2004 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 2003 : ¥1,400,000 (Direct Cost : ¥1,400,000)
There are evolutionary implications of a sex-determining system mediated by DM domain proteins beyond the sexual fate of individual animals. All metazoan species examined so far have multiple DM domain genes, and at least one such gene may be required in each species for sexual determination and/or development, suggesting that the DM domain genes may have evolved alongside the evolution of sexual reproduction in metazoans. Until now, the molecular mechanism of the ZZ/ZW-type sex-determining system in vertebrates is unknown. In this study, we characterized two Xenopus laevis genes encoding DM domains, xDMRT1 and its W-linked paralogue xDM-W. In non-mammalian vertebrates, DMRT1 is involved in testis formation. xDM-W transcripts showed transient expression in the primordial gonads of ZW tadpoles, and were more abundant than xDMRT1 transcripts during the critical period for sex determination. Interestingly, xDM-W repressed the transcriptional activity of xDMRT1. When xDM-W was overexpressed as a transgene or knocked down, a portion of the ZZ or ZW frogs, respectively, showed morphologically abnormal gonads. Collectively, these results suggest that xDM-W may be a sex (ovary)-determining (anti-testis) gene, and we propose a novel model for the ZZ/ZW-type sex determination in which xDM-W determines the development of undifferentiated gonads into ovaries by interfering with testis formation induced by xDMRT1.
Non-mammalian vertebrates may have developed a different regulatory system for DMRT1 expression or function, contributing to species diversity. In fact, in X.borealis and Silurana (X.) tropicalis, which are species closely allied to X.laevis, we could not identify a DM-W orthologue. Given these species-specific variations, we believe that DM domain genes, the sex-determining system, and species diversity could be closely related to one another.