Gonadal sex differentiation in Eleutheronema tetradactylum: Histological features and transcriptomic insights from mature gonads.

Plasticity in teleosts is a fascinating evolutionary strategy enables species to acclimate to environmental changes. However, the molecular mechanisms that underlie gonadal differentiation and reversal remain incompletely understood. The four-finger threadfin (Eleutheronema tetradactylum), a protandrous hermaphrodite belonging to the Polynemidae family, serves as an excellent model for studying genes and molecules involved in gonadal transformation. In this study, we used de novo transcriptome sequencing of the male and female gonads to identify key regulatory genes and pathways involved in sex differentiation. A total of 12,034 DEGs were identified, with 7567 upregulated and 4467 downregulated between testes and ovaries. GO and KEGG enrichment analyses identified steroid hormone biosynthesis as the key pathway in gonadal differentiation. Several novel sex biased genes DEGs were identified, including testis-biased genes nefl, rfesd, and gpatch8, and ovary-biased genes ift57, hoxb5a, naxd, and tgfbr3. furthermore, clusters of testis-specific genes, including dnah7, tspan1, hspa8, dnah3, dnah6, dnah17, myo10, kcnq3, dnaaf11, rtase, dmrt1, smcl1b, slc44a5b, tex11,cyp51 and ovary-biased genes, such as cd9, zp2, ccnp, cldnd, znf622, tc1a, hsd17b7, foxl2, sox3, and sox19a were identified, emphasizing their crucial roles in gonadal differentiation. This in-depth transcriptomic study sheds light on the molecular foundations of reproductive adaptability, offering novel insights for disciplines such as aquaculture, conservation and evolutionary biology.