Growth differentiation factor 9 of Megalobrama amblycephala: molecular characterization and expression analysis during the development of early embryos and growing ovaries.

Growth differentiation factor 9 (GDF9) is a member of the transforming growth factorβ superfamily and plays an essential role during follicle maturation in mammals. In the present study, the full-length complementary DNA (cDNA) of gdf9 was obtained from Megalobrama amblycephala. The cDNA sequence is 2,061 bp in length with an open reading frame of 1,287 bp encoding 428 amino acid residues. The deduced amino acid sequence shared identities of about 42-86 % with the homologues of other vertebrates. During the early development of embryos, the gdf9 mRNA was detected in zygote with significantly high level and declined sharply by 47 and 87 % at 4 hours post-fertilization (hpf) and 6 hpf and even to an undetectable level through advancing stages. Expression analysis based on quantitative real-time PCR revealed that gdf9 mRNA was mainly expressed in ovary, but much lower levels were also found in some nonovarian tissues. Within the follicle, gdf9 mRNA was localized both in the oocytes and the follicle layer cells by in situ hybridization. During the ovarian cycle, gdf9 mRNA significantly decreased after the previtellogenic stage and became to increase again after the fully grown stage. The results imply that Gdf9 may play critical physiological functions in M. amblycephala early embryonic development and reproduction.