Strain‐Dependent Functional Variation of a Sex Specific Sox9 Enhancer

ABSTRACT

In mammalian sex differentiation, Sox9 expression in undifferentiated gonads determines male development. Sox9 is regulated by multiple enhancers, of which Enh13/mXYSRa is the most critical. Disruption of the GATA4 binding site in Enh13/mXYSRa causes XY sex reversal in the C57BL/6J (B6J) strain, but not in the mixed genetic background of B6J × DBA/2. To clarify the cause of these differences, mice with the same mutation were generated in DBA/2. Homozygous mutants developed as XY males. We hypothesized that the phenotypic differences between strains were due to functional differences of another enhancer. Mice lacking TESCO and carrying a mutation in the GATA4 binding site were generated and analyzed. The mutants developed according to their chromosomal sex despite reduced Sox9 expression. These findings imply that the DBA/2 genetic background contains factors preventing Sox9 expression from falling below the threshold required for male development. Bulk RNA‐seq analysis of fetal gonads during sex determination identified strain‐dependent differences in intermediate mesoderm development and protease inhibition pathways; the study also revealed that the expression of Sox8 has a redundant role in Sertoli cell differentiation to that of Sox9 in male embryonic gonads. These differences may contribute to the phenotypic variation observed between strains.