Makoto Tachibana

In mammals, male and female gonads initially develop from bipotential progenitor cells, which can differentiate into either testicular or ovarian cells. The decision to adopt a testicular or ovarian fate relies on robust genetic forces, i.e., activation of the testis-determining gene Sry , as well as a delicate balance of expression levels for pro-testis and pro-ovary factors. Recently, epigenetic regulation has been found to be a key element in activation of Sry . Nevertheless, the mechanism by which epigenetic regulation controls the expression balance of pro-testis and pro-ovary factors remains unclear. Chromodomain Y-like protein (CDYL) is a reader protein for repressive histone H3 methylation marks. We found that a subpopulation of Cdyl -deficient mice exhibited XY sex reversal. Gene expression analysis revealed that the testis-promoting gene Sox9 was downregulated in XY Cdyl -deficient gonads during the sex determination period without affecting Sry expression. Instead, we found that the ovary-promoting gene Wnt4 was derepressed in XY Cdyl -deficient gonads prior to and during the sex-determination period. Wnt4 heterozygous deficiency restored SOX9 expression in Cdyl -deficient XY gonads, indicating that derepressed Wnt4 is a cause of the repression of Sox9 . We found that CDYL directly bound to the Wnt4 promoter and maintained its H3K27me3 levels during the sex-determination period. These findings indicate that CDYL reinforces male gonadal sex determination by repressing the ovary-promoting pathway in mice.