Circular RNA expression profiles and CircSnd1-miR-135b/c-foxl2 axis analysis in gonadal differentiation of protogynous hermaphroditic ricefield eel Monopterus albus

Abstract

Background The expression and biological functions of circular RNAs (circRNAs) in reproductive organs have been extensively reported. However, it is still unclear whether circRNAs are involved in sex change. To this end, RNA sequencing (RNA-seq) was performed in gonads at 5 sexual stages (ovary, early intersexual stage gonad, middle intersexual stage gonad, late intersexual stage gonad, and testis) of ricefield eel, and the expression profiles and potential functions of circRNAs were studied. Results Seven hundred twenty-one circRNAs were identified, and the expression levels of 10 circRNAs were verified by quantitative real-time PCR (qRT–PCR) and found to be in accordance with the RNA-seq data, suggesting that the RNA-seq data were reliable. Then, the sequence length, category, sequence composition and the relationship between the parent genes of the circRNAs were explored. A total of 147 circRNAs were differentially expressed in the sex change process, and GO and KEGG analyses revealed that some differentially expressed (such as novel_circ_0000659, novel_circ_0004005 and novel_circ_0005865) circRNAs were closely involved in sex change. Furthermore, expression pattern analysis demonstrated that both circSnd1 and foxl2 were downregulated in the process of sex change, which was contrary to mal-miR-135b. Finally, dual-luciferase reporter assay and RNA immunoprecipitation showed that circSnd1 and foxl2 can combine with mal-miR-135b and mal-miR-135c. These data revealed that circSnd1 regulates foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. Conclusion Our results are the first to demonstrate that circRNAs have potential effects on sex change in ricefield eel; and circSnd1 could regulate foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. These data will be useful for enhancing our understanding of sequential hermaphroditism and sex change in ricefield eel or other teleosts.

Regulatory mechanism of LncRNAs in gonadal differentiation of hermaphroditic fish, Monopterus albus

“…Previous reports have demonstrated that lncRNAs have important roles in gonadal development [ 33 – 35 ]. In M. albus, noncoding RNAs have been identified and characterized [ 20 , 36 ] . Until now, the lncRNA regulatory mechanism in gonadal development has remained unclear.…”

FoxH1 Represses the Promoter Activity of cyp19a1a in the Ricefield Eel (Monopterus albus)

“…Sections were serially cut at a thickness of 5 μm using a slicer (Leica, Nussloch, Germany) and stained with hematoxylin/eosin. The histological classification of the gonad, including the PG, previtellogenic stage (PV), EV, MLV, and OM, has been described previously [ 44 ].…”

Protein expression patterns and metal metabolites in a protogynous hermaphrodite fish, the ricefield eel (Monopterus albus)

“…Based on the transcriptome data, a few genes involved in the regulation of the sex change in the ricefield eel, such as transforming growth factor beta 3 (tgfb3), follicle stimulating hormone receptor (fshr), calcium/calmodulin dependent protein kinase 4 (camk4) and calmodulin may be the key genes, which helps balance germ cell apoptosis and proliferation during sex change [19]. Most differentially expressed genes (DEGs; mRNAs, circRNAs, and lncRNAs) were primarily enriched in the intersexual stages (IE, IL, and IM) [19][20][21]. The DEGs are involved in endocytosis, autophagy, and p53 apoptosis signaling [19].…”