Regulation of Sex-biased Gene Expression by the X-Y Chromosomal Gene Pair Kdm5c-Kdm5d in Pluripotent Cells

Mammalian sex differences are determined by the X and Y chromosomes. Ancestral homologous genes on the sex chromosomes, termed X-Y gene pairs, have been predicted to drive sex differences. However, among the five X-Y gene pairs conserved across eutherians, which pairs drive sex-biased gene expression have remained undefined. Here, we investigate the roles of the X-Y gene pair Kdm5c-Kdm5d in regulating sex-biased gene expression independently of sex hormones using pluripotent mouse embryonic stem cells (ESCs) as a model. Wild-type (WT) XX female and WT XY male ESCs significantly differ in the expression of approximately 4% of all expressed genes, classified as female- or male-biased. Loss of Kdm5c in female ESCs results in the downregulation of female-biased genes. In contrast, loss of either Kdm5c or Kdm5d in male ESCs results in the upregulation of female-biased genes and downregulation of male-biased genes, effectively neutralizing sex-biased gene expression. In male ESCs, most sex-biased genes change in expression in a similar direction upon loss of Kdm5c or Kdm5d. However, Kdm5c loss dysregulates a greater number of sex-biased genes relative to Kdm5d loss in male ESCs. Remarkably, in female ESCs ectopic Kdm5d expression is sufficient to drive a sex-biased gene expression pattern similar to that of WT male ESCs. Taken together, these results establish Kdm5c-Kdm5d as a critical X-Y gene pair in driving sex-biased gene expression in pluripotent cells. Overall design: To test the contributions of X-linked Kdm5c and Y-linked Kdm5d to sex-biased gene expression, we derived and analyzed all combinations of WT and mutant female and male mouse embryonic stem cells. Three biological replicates were analyzed per genotype.