Integrative omics reveals clues as to why Cynoglossus semilaevis pseudomales produce no W sperm

Cynoglossus semilaevis (half-smooth tongue sole) is an important aquaculture species that has a ZW/ZZ sex-determination system (females, ZW; males, ZZ). Some genotypic females may develop phenotypic males, and are known as pseudomales (ZW). These pseudomales can develop mature testes and produce sperm. However, previous studies have shown that pseudomales cannot produce sperms bearing W chromosome (W sperm). In this study, transcriptomic, proteomic, and ubiquitinated proteomic analyses were employed simultaneously to investigate the differences in gonads between pseudomales and normal males. Functional enrichment analysis of the differentially expressed genes/proteins showed that non-coding RNA metabolic processes and RNA degradation were more active in the gonads of pseudomales, and they showed higher levels of ubiquitination compared to males. In addition, most genes/proteins related to sperm morphogenesis expressed downwards in pseudomales. These genes included genes located exclusively on the Z chromosome, such as sperm flagellar protein 2 (spef2), doublesex and mab-3 related transcription factor 1 (dmrt1), doublesex and mab-3 related transcription factor 3 (dmrt3), and cilia- and flagella-associated protein 157 (cfap157). These findings characterized the transcriptional and proteomic profiles of the gonads of pseudomales and males, and suggested that W sperm were absent in pseudomales, possibly due to the disruption of sperm morphogenesis, resulting from W chromosome lacking spermatogenesis-related genes.