Examination of the role of a novel transcription factor in activating Foxl2 and its potential involvement in the regulation of ovarian development in scallops

The regulation of gonadal development remains largely unknown in bivalves, and the Foxl2 gene has been proposed as a key regulator of female development. However, limited information is available regarding its regulatory mechanisms. In our previous study on Chlamys farreri, a yeast one-hybrid assay was performed, and an unreported factor (designated Cf-FA1) that may act as a new transcription factor for activating Cf-Foxl2 tran-scription was identified. In the present study, we revealed that Cf-FA1 is a hydrophilic unstable protein pos-sessing multiple proline-rich and serine/threonine-rich regions. Cf-FA1 exhibited a significantly biased expression in the ovary detected by semi-quantitative RT-PCR, and its cyto-localization was exhibited in ovarian cells during oogenesis through in situ hybridization and immunohistochemistry, while not in male gametes during spermatogenesis. Western blotting demonstrated that Cf-FA1 protein also exhibited a similar sexually dimorphic expression pattern and was more concentrated in the nucleus along with ovarian maturation. ChIP assays confirmed that Cf-FA1 binds to the Cf-Foxl2 promoter. Furthermore, the interference of Cf-FA1 expression in the ovary by in vivo RNAi led to an obvious Cf-Foxl2 expression decrease, ovary developmental retardation, gonadosomatic index decline, and female gametes reduction. These results suggest that Cf-FA1 acts as a tran-scription factor to activate Foxl2 transcription and participates in ovarian development and oogenesis regulation in bivalves, providing an important basis for sex control breeding in aquaculture.