Disruption of Sex-Linked Causes ZW Female-to-Male Sex Reversal in the Japanese Frog .

is an ancestral homologous gene of the male-determining in eutherian mammals and determines maleness in medaka fish. In the Japanese frog, , is located on the Z and W chromosomes. To assess the sex-determining function of in this frog, we investigated its expression in gonads during early tadpole development and conducted genome-editing experiments. We found that the mRNA levels in the gonads/mesonephroi were much higher in ZW females than that in ZZ males, and that the W-borne allele was dominantly expressed. A higher expression in ZW females preceded the onset of the sexually dimorphic expression of other autosomal sex differentiation genes. The Sox3 protein was detected by immunostaining in the somatic cells of early tadpole gonads around the boundary between the medulla and cortex in ZW females, whereas it was outside the gonads in ZZ males. Disrupting using TALEN, which targets two distinct sites, generated sex-reversed ZW males and hermaphrodites, whereas no sex reversal was observed in ZZ males. These results suggest that the sex-linked is involved in female determination in the ZZ-ZW sex-determining system of the frog, an exact opposite function to the male determination of medaka and eutherian .