The role of β-catenin in ovarian differentiation by upregulation cyp19a1a in a natural triploid teleost, Qi River crucian carp (Carassius auratus).

The Qi River crucian carp (Carassius auratus), a gynogenetic all-female fish, reproduces both unisexually and sexually, but the underlying molecular mechanisms remain unclear. The Wnt/β-catenin pathway influences mammalian ovarian development via cytochrome P450 family 19 subfamily A member 1 (CYP19A1) activation, however, its role in teleosts is poorly understood. Here, we investigated β-catenin's involvement in gonadal differentiation through histological and molecular analyses. Histological examination with Hematoxylin and Eosin (HE) staining and immunohistochemistry showed that oogonia emerged in female gonads at 15 days after hatching (dah), undergoing mitotic proliferation between 20 and 25 dah, and transitioning to meiosis from 25 to 30 dah. Significantly, β-catenin exhibited synchronized upregulation with cyp19a1a during the gonadal differentiation window, indicating functional synergy. Cellular co-localization studies further revealed β-catenin and cyp19a1a co-expressed in both germline (oogonia/oocytes) and somatic compartments, while pharmacological inhibition of β-catenin with quercetin and RNA interference via injection of β-catenin double-stranded RNA both significantly suppressed cyp19a1a expression. Mechanistically, promoter analysis demonstrated that β-catenin-Lef1 complexes directly activate cyp19a1a transcription through conserved T-cell factor (TCF)/lymphoid enhancer factor (LEF) response elements. The study identifies β-catenin as a key regulator of ovarian differentiation in Qi River crucian carp by coordinating cyp19a1a expression, offering initial experimental evidence for the role of Wnt/β-catenin signaling in sustaining unisexual reproduction. This work advances our understanding of evolutionary conserved versus species-specific mechanisms in teleost sex differentiation systems.