Integrated application of transcriptomics and metabolomics provides insights into sexual dimorphism in Apostichopus japonicus

Sea cucumber (Apostichopus japonicus) is a commercially important aquaculture species in China. Research findings have indicated that adult male sea cucumbers with differentiated gonads have a greater growth advantage compared to females. Understanding the molecular basis of sexual dimorphism in A. japonicus is critical for developing sex control breeding strategies in aquaculture. In this study, we integrated transcriptomic and metabolomic analyses of testes and ovaries to elucidate differences in gene expression and metabolite profiles. Key sex-biased genes, including cyp2 subfamily members, cpeb1, and sult1e1, were predominantly expressed in the ovaries, whereas sac and catsper4 showed specific expression in the testes, suggesting their potential roles in sex development. Moreover, compared to the ovaries, the testes exhibited significantly higher expression of immune-related genes (myosin-9, formin-like, and vwde), along with greater abundance of metabolites such as astaxanthin and ferulate, suggesting that males may possess stronger immune capacity than females. Higher expression levels of ugts in differentiated ovaries compared to testes suggest that female gonads may possess greater nutritional value due to their role in saponin biosynthesis. Additionally, pathway enrichment analyses revealed that ovaries exhibited enhanced carbon metabolism, amino acid biosynthesis, and purine and pyrimidine metabolism, suggesting that the higher energy demands of oogenesis compared to spermatogenesis may contribute to sexual dimorphism in growth. These findings provide novel insights into sex-biased metabolic and regulatory mechanisms and lay a foundation for future studies aimed at elucidating the regulatory mechanisms of gonadal development in sea cucumbers.