Gene identification and functional analysis of a D-type cyclin (CCND2) in freshwater pearl mussel (Hyriopsis cumingii)

Background Cyclin D (CCND) plays an important role in the cell cycle and is a rate-limiting factor that facilitates the G1/S transition. Methods In this study, the full-length cDNA of Hc-CCND2 was isolated from freshwater pearl mussel (Hyriopsis cumingii; Hc) and amplified using the 3 '/5 ' RACE system. The Hc-CCND2 expression profiles were analysed by quantitative real-time PCR. Functional analysis of the Hc-CCND2 genes was examined by both RNA interference (RNAi) and overexpression in H. cumingii. Results Hc-CCND2 protein sequences were 295 amino acids long, possessed D-type cyclin signature motifs and contained conserved cyclin box domains. Hc-CCND2 was expressed in all examined tissues (adductor, foot, visceral mass, gill, outer mantle, inner mantle and gonad), with the highest expression levels found in the gill (P < 0.05). During the different developmental periods of the embryo, the relative expression of Hc-CCND2 increased with embryonic development, peaking at the blastula stage and decreasing significantly in the gastrula stage. After knockdown of Hc-CCND2 by RNAi, a significant decrease in CDK6 expression levels was found, while the percentage of cells in the G0/G1 phase significantly increased. Overexpression of Hc-CCND2 in mantle cells led to increased proliferation of cultured cells (P < 0.05). Conclusions Our results demonstrated that Hc-CCND2 may promote cell cycle progression in H. cumingii, and that overexpression of Hc-CCND2 promotes mantle cell proliferation. These findings may provide a novel approach for improving the slow proliferation rate of shellfish cells in in vitro cultures.

Automated summary

This study found that the Hc-CCND2 gene is widely expressed in freshwater pearl mussel and plays an important role in the cell cycle. Overexpression of Hc-CCND2 promotes cell proliferation, which is significant for improving the proliferation rate of shellfish cells in in vitro cultures.