Circtefb Regulates Myocytes Development by Sponging Pol-miR-138 in Japanese Flounder (Paralichthys olivaceus)

Circular RNAs (circRNAs) are a type of endogenous competitive RNA that can perform various functions and regulate a number of biological activities in organisms. Many studies have shown that circRNAs can modulate skeletal muscle development in animals. However, the effects of circRNAs on the skeletal muscle development of Japanese flounder and its regulatory mechanisms remain unclear. We screened circRNA_2111 from previously obtained transcriptomic data related to Japanese flounder skeletal muscle development. Derived from the tefb gene, it has been designated as circtefb. Circtefb was formed by the reverse splicing of two exons of tefb. Circtefb was more stable than its corresponding linear RNA. There was a significant difference in the expression of circtefb at different stages P1 (90 d), P2 (12 months) and P3 (24 months) of Japanese flounder (p<0.05). Over-expression of circtefb in Japanese flounder myocytes resulted in a significant upregulation of proliferation marker genes ccnd1, ccnd2a and pcna (p<0.05), suggesting that it promoted proliferation of Japanese flounder myocytes. The expressions of ccnd1, ccnd2a, and pcna were significantly decreased after the transfection of pol-miR-138 into Japanese flounder myocytes (p<0.05). In addition, circtefb can suppress pol-miR-138 function by binding to it, which was detected by dual-Luciferase reporter assay and co-transfection of circtefb and pol-miR-138, thereby promoting the proliferation of Japanese flounder myocytes. The results indicated the function of circRNAs in Japanese flounder muscle development,, which is also helpful to understand the growth and development of other fish species.