The specific expression profile and function of circular RNAs (circRNAs) in mammalian ovarian follicles, especially during the atresia process, are unclear. In this study, genome-wide deep circRNA sequencing was applied to screen circRNAs in healthy and early atretic antral follicles in pig ovaries. A total of 40,567 distinct circRNAs were identified in follicles, among which 197 circRNAs (108 upregulated and 89 downregulated) were significantly shifted during the early atresia process. Most differentially expressed circRNAs (DECs) lacked protein-coding potential. Annotation analysis of the DECs revealed 162 known host genes, or noncoding RNAs, and 10 intergenic regions. The key pathways in which these host genes are involved include the focal adhesion-PI3K-Akt-mTOR signaling pathway, vascular endothelial growth factor A (VEGFA)–vascular endothelial growth factor receptor 2 signaling pathway and transforming growth factor-beta signaling pathway. Further comparison analysis between host genes of DECs and the differentially expressed linear messenger RNA transcripts revealed the cotranscription of circRNAs and their linear mRNAs in inhibin beta units (INHBA and INHBB), glutathione S-transferase (GSTA1), and VEGFA. In addition, we predicted 196 pairs of potential circRNA-micro RNA (miRNA) interactions among 77 DECs and 101 porcine miRNAs. We have identified 16 functional miRNAs by comparing the 101 miRNAs to the functional miRNAs reported in mammal ovarian follicle atresia and granulosa cell apoptosis studies. Our study adds new knowledge to circRNA distribution profiles in pig ovarian follicles, offers a valuable reference for transcriptomic profiles in the initiation of follicular atresia, highlights warranted circRNAs for further functional investigation, and provides possible biomarkers for ovarian dysfunctions.

尚不清楚哺乳动物卵巢卵泡中环状RNA（circRNA）的特异性表达谱和功能，尤其是在闭锁过程中。在这项研究中，全基因组的深circRNA测序技术被用于筛选健康和早期卵巢卵巢中闭角窦卵泡中的circRNA。在卵泡中共鉴定出40,567个不同的circRNA，其中197个circRNA（108个上调和89个下调）在早期闭锁过程中发生了显着移位。大多数差异表达的circRNA（DECs）缺乏蛋白质编码的潜力。DEC的注释分析显示了162个已知宿主基因或非编码RNA，以及10个基因间区域。这些宿主基因参与的关键途径包括粘着性PI3K-Akt-mTOR信号传导途径，血管内皮生长因子A（VEGFA）–血管内皮生长因子受体2信号通路和转化生长因子-β信号通路。DECs宿主基因与差异表达的线性信使RNA转录本之间的进一步比较分析显示，在抑制素β单元中circRNA及其线性mRNA的共转录（INHBA和INHBB），谷胱甘肽S-转移酶（GSTA1）和VEGFA。此外，我们预测了77个DEC和101个猪miRNA之间存在196对潜在的circRNA-micro RNA（miRNA）相互作用。通过将101个miRNA与哺乳动物卵巢滤泡闭锁和颗粒细胞凋亡研究中报道的功能性miRNA进行比较，我们已经鉴定出16个功能性miRNA。我们的研究为猪卵巢卵泡中的circRNA分布图增加了新的知识，为卵泡闭锁的起始转录组图谱提供了有价值的参考，强调了有担保的circRNAs可以用于进一步的功能研究，并为卵巢功能障碍提供了可能的生物标记。