Sex Determination and Differentiation in Fish

Sex determination and gonadal differentiation vary considerably in fish. The medaka, Oryzias latipes, has two major advantages for genetic research: a large genetic diversity within the species and the existence of several inbred strains. Using positional cloning and detailed sequence analysis of BAC clones, we have recently identified Z)A/y (DM-related gene on the Y chromosome) as a strong candidate for the sex-determining gene (DMY) of medaka, which possess and XY system. DMY contains the highly conserved DM domain found in other genes involved in sexual development in both vertebrates and invertebrates. Expression analysis during early embryogenesis shows that DMY 15 found in the somatic cells of the XY gonads at the time when sex determination occurs. Two naturally occurring XY female mutants established DMTs critical role in male development. DMK provides the first example of a sex-determining gene in non-mammalian vertebrates.