A timecourse analysis of gonadal histology and transcriptome during the sexual development of yellow catfish, Pelteobagrus fulvidraco.

Yellow catfish (Pelteobagrus fulvidraco), as an important aquatic species, exhibiting pronounced sexually dimorphic growth patterns. However, the molecular mechanism underlying sexual differentiation in yellow catfish remains a mystery. In this study, we performed histological analysis to identify the critical period of gonadal sex differentiation in P. fulvidraco, Our results showed that the differentiation of male and female gonads did not occur synchronously. The ovarian cavities formation in female occurred at 7 days post-hatching (DPH), followed by the emergence of primordial glandular cells at 25 DPH, whereas male gonadal differentiation initiated later, at 35 DPH. Pseudotemporal analysis was used to infer the developmental trajectories of male and female yellow catfish, highlighting rapid differentiation of individual traits from 7 DPH to 30 DPH. Additionally, timecourse comparative transcriptomic analysis identified several female biased genes, including Foxl2a, Foxl2b, Cyp19a1, zar1l, Rbpms2, as well as chromosomal-structure related genes such as Banf2, npm, Top1b, and H2AA, suggesting a female specific differentiation pattern and ovarian development bias following maturation. In contrast, male-biased genes such as dmrt1 show similar expression patterns in both sexes during the early stage of differentiation, but become male-specific in mature gonads, indicating a regulatory shift from post-transcriptional to expression regulation during sex differentiation. In situ hybridization analysis further confirms the localization of Foxl2a and Foxl2b in early-stage oocytes, and Top1b in early germ cells of mature gonads. This study systematically investigated the early gonadal differentiation process and provided fundamental data for future research on sex determination regulation mechanism in yellow catfish. These findings also offer valuable insight for industrial applications, including single-sex breeding and regulation of ovarian development in Pelteobagrus fulvidraco.