Deletion of Ybx1 results in germ cell hypoplasia in mouse embryos

Several evolutionarily conserved genes have been reported to be involved in gametogenesis. Y-box binding proteins, which have a conserved nucleotide-binding cold-shock domain, have been reported in both vertebrates and invertebrates. Although homologues of Ybx1 in Drosophila and zebrafish play important roles in oogenesis, the involvement of mouse Ybx1 in gametogenesis or gonadal development remains unclear. In this study, we investigated the female and male fetal gonadal phenotypes in Ybx1 knockout mice. Embryos of Ybx1 knockout mice at E13.5 showed slender gonads compared to those of the controls. Whole-mount gonadal immunostaining revealed a significant decrease in the number of female embryonic germ cells. Immunocytochemistry revealed that YB-1, a protein encoded by Ybx1, is expressed in both germ and gonadal somatic cells. In contrast, transcriptome analysis of germ cells and gonadal somatic cells at E13.5 revealed that deletion of Ybx1 did not cause global changes in gene expression. However, Anapc5 and Rpn1, which have been implicated in germ cell survival, were significantly downregulated in Ybx1(–/–) female germ cells. Furthermore, Acta2 and Mmp2, known Ybx1-regulated genes, were also significantly downregulated in Ybx1(–/–) female gonadal somatic cells, potentially contributing to germ cell hypoplasia. Collectively, our results suggest that YB-1 may have a role in gonadal development by promoting germ cell survival and gonadal development.