Investigation of the role of endogenous miRNAs in determining sterility in triploid Pacific oysters (Crassostrea gigas)

Triploid oysters generate fewer gametes than diploid oysters and exhibit varying degrees of gonad development. The expression of related genes, such as those involved in gametogenesis and energy metabolism, may influence reproductive potential. In addition, microRNAs (miRNAs) are important regulators of gene expression. However, the contribution of miRNAs has not yet been assessed in sterile triploid Pacific oysters (Crassostrea gigas). We therefore obtained extensive miRNA and gene expression data to identify potentially critical miRNA-mRNA interactions that are linked to sterility in triploid C. gigas. Here, we found miR-263-x to be significantly down -regulated in the gonads of sterile females. The upregulated target genes were associated with lipid droplet formation, which revealed the likely involvement of nutrient accumulation during gonadal development as regulated by miR-263-x in female sterile triploids. In males, the upregulated miRNAs (miR-1992-y and miR-2001-x) were shown to regulate spermatogenesis-related gene expression, including flagellar formation, and cell proliferation and migration. Our results suggest that energy redistribution regulated by miRNAs may be critical for gonad development in females, indicating that sterile triploids undergo a significant reduction in gamete number and show an increased accumulation of nutrients in the gonads. Our findings further indicate that decreased expression of genes related to spermatogenesis regulated by miRNAs is important in gonadal dysgenesis in sterile triploids. These results shed light on the epigenetic regulatory mechanisms governing ste-rility in triploid bivalves.

Automated summary

In sterile triploid Pacific oysters, miR-263-x is significantly down-regulated in the gonads of females, and the upregulated target genes are associated with lipid droplet formation, suggesting the likely involvement of nutrient accumulation during gonadal development as regulated by miR-263-x. Additionally, in males, the upregulated miRNAs miR-1992-y and miR-2001-x regulate spermatogenesis-related gene expression, including flagellar formation, cell proliferation, and migration.