Molecular characterization and expression of the feminization-1c (fem-1c) in the freshwater mussel (Hyriopsis cumingii)

The feminization-1c (fem-1c) gene has been shown to be associated with sex differentiation and determination in many metazoan species. It belongs to the fem-1 family which is a member of the ANK superfamily. In this study, the full-length cDNA of the fem-1c (Hcfem-1c) gene was isolated from the freshwater mussel (Hypriopsis cumingii). The isolated Hcfem-1c cDNA was 2196 bp in length and encoded a putative protein of 621 amino acids that contains seven ANK domains. Phylogenetic analysis of the deduced HcFEM-1C protein showed that it clustered with the other invertebrates homologues, indicating that the sequence of HcFEM-1C was conserved during evolution. Quantitative real-time PCR (qPCR) expression revealed that the Hcfem-1c gene was expressed in the adductor muscle, foot, liver, gill, kidney, mantle, and gonads of male and female adult mussels (two years old). In the gonads Hcfem-1c was much less abundant in males than that in females. During early development of the gonads, Hcfem-1c transcripts were significantly increased in the primordial germ cell differentiation stage (5 months old). We hypothesized that Hcfem-1c probably regulates female gonad differentiation. In situ hybridization showed that a strong and specific signal concentrated in the female oocyte cell membrane and male follicular wall, indicating that Hcfem-1c gene may not only be involved in female gonad differentiation, but also participates in egg development. This study laid the foundations for a better understanding of gender differentiation mechanism in H. cumingii.