The genome-wide identification and gonad-specific expression analysis of the PfTSSK gene family in Pinctada fucata.

Pinctada fucata is a crucial marine pearl oyster species for pearl culture, and the regulation of gonadal maturation is essential for pearl oyster breeding. This study investigates the genetic characteristics and expression patterns of the testis-specific serine/threonine kinase family (PfTSSK) in this species. A total of six PfTSSK genes were identified, namely PfTSSK1, PfTSSK1-like, PfTSSK3, PfTSSK4, PfTSSK5, and PfTSSK7, among which PfTSSK1-like is a newly reported member in P. fucata. Phylogenetic and conserved motif analyses indicated that these genes are highly conserved among bivalves, but exhibit evolutionary divergence compared to those in mammals. The cis-regulatory element analysis suggests that this gene family may influence growth and developmental processes through gene regulation. Expression profile analysis revealed that PfTSSK genes are most highly expressed in the testes, particularly during testicular maturation, while their expression in the ovaries is lower but synchronized with female gametogenesis. In situ hybridization results demonstrated that PfTSSK are expressed in various cells within both the testes and ovaries, suggesting their involvement in the development of both male and female gametes. This study provides new insights into the molecular mechanisms underlying bivalve reproductive development and lays a theoretical foundation for the molecular regulatory network governing gonadal development and gametogenesis.