Genome-wide characterization of the FOX gene family reveals sex-biased expression and FoxO-associated regulation during gonadal development in Bellamya aeruginosa.
Forkhead box (FOX) transcription factors are important regulators of development and reproduction, but their roles in molluscan gonadal development remain unclear. In this study, the FOX gene family was systematically identified in the freshwater gastropod Bellamya aeruginosa, and comparative gonadal transcriptomic analyses were performed across sexes and developmental stages.A total of 35 FOX genes were identified and classified into 19 subfamilies. Phylogenetic and synteny analyses indicated that the FOX gene family is generally conserved among mollusks, whereas FoxG and FoxL2 showed lineage-specific expansion. Structural analyses demonstrated that most BaeFOX proteins retained the conserved Forkhead domain architecture. Transcriptomic analyses revealed that gene expression divergence between testes and ovaries was markedly greater than that between developmental stages within the same gonad, indicating that sexual dimorphism is the major source of gonadal transcriptional variation. Functional enrichment consistently identified the FoxO signaling pathway in sex-biased comparisons. Several FOX genes also displayed clear gonad-biased expression patterns, and network analyses suggested that BaeFoxO, BaeFoxL2, and BaeFoxG may play central regulatory roles in gonadal development. These findings provide the first comprehensive characterization of the FOX gene family in B. aeruginosa and suggest that FOX-related regulatory networks potentially participate in gonadal development in gastropod mollusks.