Gonadogenesis in scallop Chlamys farreri and Cf-foxl2 expression pattern during gonadal sex differentiation

Gonad development and sexual differentiation are important biological processes. More insight is needed in these processes to improve selection and breeding efficiency in the production of culture animals for monosex farm operations of commercially important shellfish species. Foxl2 is the earliest known sex dimorphic marker of ovarian differentiation in mammals, but studies on foxl2 in invertebrate species are rare. This study revealed the gonadogenesis and expression characteristics of foxl2 during the gonadal differentiation in the scallop Chlamys farreri, an important commercial mollusk in China. The result showed that C. farreri gonad becomes visible once juveniles reach a shell height of 5.5 mm. Sex can be distinguished based on gonad histology in animals with a minimum shell height of 9 mm. Expression of Cf-foxl2 (C. farreri foxl2) was first observed in cytoplasm of ovarian germ and follicle cells, just after the initiation of ovarian differentiation. Results indicate that Cf-foxl2 can be used as an early sex-marker gene, and may have participated in the regulation of ovary differentiation in C. farreri.