DMRT1-mediated regulation of TOX3 modulates expansion of the gonadal steroidogenic cell lineage in the chicken embryo

During gonadal sex determination, the supporting cell lineage differentiates into Sertoli cells in males and pre-granulosa cells in females. Recently, single cell RNA-seq data have indicated that chicken steroidogenic cells are derived from differentiated supporting cells. This differentiation process is achieved by a sequential upregulation of steroidogenic genes and downregulation of supporting cell markers. The exact mechanism regulating this differentiation process remains unknown. We have identified TOX3 as a previously unreported transcription factor expressed in embryonic Sertoli cells of the chicken testis. TOX3 knockdown in males resulted in increased CYP17A1-positive Leydig cells. TOX3 overexpression in male and female gonads resulted in a significant decline in CYP17A1-positive steroidogenic cells. In ovo knockdown of the testis determinant DMRT1 in male gonads resulted in a downregulation of TOX3 expression. Conversely, DMRT1 overexpression caused an increase in TOX3 expression. Taken together, these data indicate that DMRT1-mediated regulation of TOX3 modulates expansion of the steroidogenic lineage, either directly, via cell lineage allocation, or indirectly, via signaling from the supporting to steroidogenic cell populations.

Automated summary

During gonadal sex determination, supporting cells differentiate into Sertoli cells in males and pre-granulosa cells in females. Recent single cell RNA-seq data suggests that chicken steroidogenic cells are derived from differentiated supporting cells. The exact mechanism regulating this differentiation process remains unknown. TOX3 has been identified as a previously unreported transcription factor expressed in embryonic Sertoli cells of the chicken testis. TOX3 knockdown in males leads to an increase in CYP17A1-positive Leydig cells, while TOX3 overexpression in both male and female gonads results in a significant decline in CYP17A1-positive steroidogenic cells. In male gonads, knockdown of the testis determinant DMRT1 leads to a downregulation of TOX3 expression, whereas DMRT1 overexpression causes an increase in TOX3 expression. These findings suggest that DMRT1-mediated regulation of TOX3 plays a role in modulating the expansion of the steroidogenic lineage.