CircRNA profiling reveals circ880 functions as miR-375-3p sponge in medaka gonads

Circular RNAs (circRNAs) have been regarded as regulators in the biological processes of various species. However, there is no report about circRNAs in the gonads of model fish medaka (Oryzias latipes). In this study, 1157 and 1570 circRNAs were obtained in the ovary and testis by RNA-sequencing. The characteristics of circRNAs were explored in sequence length, exon composition, and chromosome position. 24 circRNAs were significantly up or down-regulated in the testis compared to the ovary, 9 of which were verified by qRT-PCR. Interestingly, circ452 was highly expressed in the testis while circ880 expression exhibited sexual dimorphism. In situ hybridization (ISH) revealed that circ452 and circ880 were expressed in meiotic germ cells, and circ880 was also abundant in spermatogonia. In addition, dual-luciferase reporter assay manifested that circ880 and Oldnd can combine with miR-375-3p. Overall, these results provide emerging circRNA libraries and open new avenues for future investigation of circRNAs in medaka.

Automated summary

This study identified a large number of circRNAs in the ovaries and testes of medaka through RNA sequencing, with some circRNAs showing significant differential expression between the testis and ovary. Experimental validation confirmed that a subset of circRNAs can interact with miRNAs and are expressed in reproductive cells.