Tracing the Emergence of a Novel Sex-Determining Gene in Medaka,Oryzias luzonensis

Abstract

Three sex-determining (SD) genes, SRY (mammals), Dmy (medaka), and DM-W (Xenopus laevis), have been identified to date in vertebrates. However, how and why a new sex-determining gene appears remains unknown, as do the switching mechanisms of the master sex-determining gene. Here, we used positional cloning to search for the sex-determining gene in Oryzias luzonensis and found that Gsdf^Y (gonadal soma derived growth factor on the Y chromosome) has replaced Dmy as the master sex-determining gene in this species. We found that Gsdf^Y showed high expression specifically in males during sex differentiation. Furthermore, the presence of a genomic fragment that included Gsdf^Y converts XX individuals into fertile XX males. Luciferase assays demonstrated that the upstream sequence of Gsdf^Y contributes to the male-specific high expression. Gsdf is downstream of Dmy in the sex-determining cascade of O. latipes, suggesting that emergence of the Dmy-independent Gsdf allele led to the appearance of this novel sex-determining gene in O. luzonensis.