W chromosome copy number is associated with DNA methylation remodeling and steroid hormone metabolism in the gonads of sterlets (Acipenser ruthenus)

In sturgeons with a ZZ/ZW sex chromosome system, the W chromosome is female-specific and is closely associated with sex determination and gonadal differentiation. However, the mechanisms by which the W chromosome regulates gonadal differentiation remain largely unknown. In this study, gynogenetic diploid sterlets (Acipenser ruthenus) with three W chromosome copy number genotypes, ZZ, ZW, and WW, were used to characterize molecular differences associated with W chromosome copy number in the gonads. Histological analysis showed that ZZ individuals exhibited testicular characteristics, whereas both ZW and WW individuals displayed typical ovarian morphology. Genome-wide DNA methylation analysis revealed distinct methylation patterns among the three genotypes despite similar global CpG methylation levels. Transcriptomic analysis further revealed distinct gene expression profiles among the three genotypes, with differentially expressed genes commonly enriched in the Steroid hormone biosynthesis pathway. Several genes involved in steroid hormone biosynthesis and metabolism, including hsd17b7, hsd17b2, hsd17b12-b, hsd3b, cyp17a1, comt, and srd5a3, showed progressively increased expression with increasing W chromosome copy number. Integration of promoter DNA methylation and gene expression identified a subset of genes exhibiting coordinated methylation and transcriptional changes, which were mainly involved in lipid metabolic processes closely related to steroid hormone biosynthesis. Together, these results reveal distinct DNA methylation and gene expression patterns associated with W chromosome copy number, with coordinated molecular changes involving lipid metabolism and steroid hormone biosynthesis. These findings provide new insights into the transcriptional and epigenetic regulation associated with W chromosome copy number in sturgeon gonads, offering a comparative perspective on the evolution of sex differentiation mechanisms between chondrosteans and teleosts.