Comparative analysis demonstrates cell type-specific conservation of SOX9 targets between mouse and chicken.

SRY (sex-determining region Y)-box 9 (SOX9) is a transcription factor regulating both chondrogenesis and sex determination. Among vertebrates, SOX9's functions in chondrogenesis are well conserved, while they vary in sex determination. To investigate the conservation of SOX9's regulatory functions in chondrogenesis and gonad development among species, we performed chromatin immunoprecipitation sequencing (ChIP-seq) using developing limb buds and male gonads from embryos of two vertebrates, mouse and chicken. In both mouse and chicken, SOX9 bound to intronic and distal regions of genes more frequently in limb buds than in male gonads, while SOX9 bound to the proximal upstream regions of genes more frequently in male gonads than in limb buds. In both species, SOX palindromic repeats were identified more frequently in SOX9 binding regions in limb bud genes compared with those in male gonad genes. The conservation of SOX9 binding regions was significantly higher in limb bud genes. In addition, we combined RNA expression analysis (RNA sequencing) with the ChIP-seq results at the same stage in developing chondrocytes and Sertoli cells and determined SOX9 target genes in these cells of the two species and disclosed that SOX9 targets showed high similarity of targets in chondrocytes, but not in Sertoli cells.