Dynamic expression and functional analysis of circular RNA in the gonads of Chinese soft-shelled turtles (Pelodiscus sinensis)

Circular RNA (circRNA) is a noncoding RNA that can regulate a variety of biological processes. CircRNAs can regulate gene expression posttranscriptionally by acting as microRNA sponges. Many turtle species are remarkable organisms due to their reproductive processes. However, information on circRNA in the gonads of turtles is limited. In this study, 6, 121 circRNAs were identified in the testes and ovaries of Chinese soft-shelled turtles (Pelodiscus sinensis) using the Illumina platform, and 710 circRNAs were significantly differentially expressed (DE). The DE circRNAs included 541 upregulated and 169 downregulated circRNAs in the testes. GO and KEGG pathway analysis indicated that the DE circRNAs were enriched in several signaling pathways, including GnRH, Wnt, FoxO, Progesterone mediated oocyte maturation, and mTOR signaling pathways. Five DE circRNAs were randomly selected, and their relative expression levels in ovaries and testes were detected by quantitative real-time PCR. All of these circRNAs were differentially expressed. In addition, 9, 883 interactions between circRNAs and miRNAs were predicted in the turtles. Target genes of the miRNAs include a range of genes regulating gonadal development. Seven ceRNA networks (DE circRNAs-DE miRNAs-DE mRNAs), including 7 DE circRNAs, 11 DE miRNAs and 20 DE mRNAs, were constructed. The networks included Cdc6, the miR-1 family, the miR-203 family, and the miR-302 family. The expression profile of gonadal circRNAs might help to elucidate the roles of nonprotein coding RNAs in turtle gonadal development.