Sex- and stage-dependent expression of gonadal soma-derived factor paralogues reveals functional and evolutionary divergence in European sea bass (Dicentrarchus labrax)

Introduction The gonadal soma-derived factor (Gsdf) is a member of the Transforming Growth Factor-β (TGF-β) superfamily, with key roles in teleost reproduction, particularly in males. Previously considered teleost-specific, its presence in non-teleostvertebrates indicates a more ancient evolutionary origin. It is still classified as an orphan ligand with uncharacterized signaling pathways, and its evolution, regulatory mechanisms, and functional divergence remain unclear. Methods The roesent work provides a comprehensive characterization of two gsdf paralogues in European sea bass ( Dicentrarchus labrax ), integrating phylogenetic, synteny, transcriptional regulation, and protein localization analyses, together with stage-specific gene expression profiling during ontogeny, puberty onset and adult reproductive cycle. Results Phylogenetic reconstruction of 31 species revealed that gsdf duplications are independent, lineage-specific events unrelated to the teleost-specific whole genome duplication (3R). Synteny analyses showed that gsdf1 retains strong conservation with ancestral loci, whereas gsdf2 resides in a distinct but conserved genomic context, suggesting complex rearrangement. Comparative promoter analysis identified conserved transcription factor binding sites, supporting a shared regulatory framework across teleosts. Expression profiling revealed that both paralogues are gonad-enriched, expressed from early gonadal differentiation, and downregulated at the onset of precocious male puberty. In adults, gsdf1 was predominantly expressed in males, especially during pre-meiotic stages, while gsdf2 was more abundant in females, particularly in follicular cells during pre-vitellogenesis. Immunolocalization confirmed stage- and sex-specific presence in Sertoli and follicular cells, indicating local action. Conclusions These results support the subfunctionalization of gsdf paralogues in sea bass, with sexspecific partitioning of reproductive roles, and provide new insight into the evolutionary plasticity of gonad-related genes in teleosts.