Molecular cloning and sexually dimorphic expression patterns of nr0b1 and nr5a2 in olive flounder, Paralichthys olivaceus.

The nr0b1 and nr5a2 genes, members of the nuclear receptor superfamily, are strong candidate genes involved in gonadal differentiation in several vertebrate species. In this study, an nr0b1 complementary DNA (cDNA) of 1446 bp, which encodes a predicted 298 amino acid protein, and an nr5a2 cDNA of 2425 bp, which encodes a deduced 523 amino acid protein, were obtained from olive flounder Paralichthys olivaceus. Both genes were expressed in multiple organ tissues of adult flounder, with a higher expression in ovary than in testis. Quantitative real-time RT-PCR was performed to investigate their temporal expression profiles in gonads during differentiation and at five development stages. Results indicated that nr0b1 and nr5a2 were expressed in primitive gonad and in the ensuing gonadal differentiation periods. In general, both genes were more highly expressed in ovary than in testis at all observed development stages. The expression level of cyp19a correlated with the nr5a2/nr0b1 ratio over the course of flounder gonadal differentiation; hence, nr0b1 and nr5a2 genes may be involved in flounder ovarian differentiation by regulating the expression of cyp19a.