Résumé
The gonad-specific transcription factor DMRT1 is considered as the Testis Determining Factor in many vertebrates. In mammals, SRY is the testis-determining gene, and according to the mouse species, DMRT1 has no longer function in testis determination since Dmrt1 disruptions only affect post-natal testis differentiation and fertility. Nevertheless, human patients with DMRT1 mutations exhibit 46, XY DSD with testicular dysgenesis, suggesting an earlier role for DMRT1 in non-rodent mammals. Thanks to CRISPR/Cas9 technology, our laboratory generated DMRT1 mutant rabbits. We showed that the absence of DMRT1 leads to early male-to-female sex reversal in XY homozygous mutants that developed ovaries. Indeed, when observed a few days after sex determination, XY DMRT1-/- gonads were devoid of testis cords structures and presented a typical ovarian organization with a thicker epithelium and ovigerous cords. Molecular studies confirmed the ovarian signature with an up-regulation of ovary-driving genes (RSPO1, WNT4, FOXL2, and CYP19A1) and downregulation of testis-specific genes (SOX9, SOX10, and DHH) in the developing XY DMRT1-/- gonads (bulk RNA-sequencing and RT-qPCR data). Interestingly, although some SOX9 protein remained detectable in a few somatic cells, it was not sufficient to trigger its target gene expression. Our data highlight the role of DMRT1 as a key player in sex determination in rabbits. DMRT1 is required for SRY action on SOX9 gene expression and may also be necessary for SOX9 protein function on its target genes acting as a pioneer factor. Our investigations are currently focused on characterizing DMRT1 direct targets in the rabbit gonads by ChIP-seq.