Differential Expression and Functional Analysis of CircRNA in the Ovaries of Low and High Fecundity Hanper Sheep

Litter size is a considerable quality that determines the production efficiency of mutton sheep. Therefore, revealing the molecular regulation of high and low fertility may aid the breeding process to develop new varieties of mutton sheep. CircRNAs are the important factors regulating follicular development, but their mechanism role in the regulation of litter size in Hanper sheep is not clear. In the present study, ovarian tissues from the follicular (F) or luteal phase (L) of Hanper sheep that were either consecutive monotocous (M) or polytocous were collected. Then, we performed transcriptome sequencing to screen for differentially expressed circRNAs (DE-circRNAs) and elucidate their function. In total, 4256 circRNA derived from 2184 host genes were identified in which 183 (146 were upregulated, while 37 were downregulated) were differentially expressed in monotocous sheep in the follicular phase versus polytocous sheep in the follicular phase (MF vs. PF). Moreover, 34 circRNAs (14 were upregulated, while 20 were downregulated) were differentially expressed in monotocous sheep in the luteal phase versus polytocous sheep in the luteal sheep (ML vs. PL). This was achieved through DE-circRNAs function enrichment annotation analysis by GESA, GO, and KEGG, which function through the EGF-EGFR-RAS-JNK, TGF-β and thyroid hormone signaling pathway to affect the litter size of Hanper sheep in MF vs. PF and ML vs. PL. STEM results showed that MAPK signaling pathways play a key role in MF vs. PF and ML vs. PL. Through WGCNA analysis, AKT3 was a core gene in MF vs. PF and ML vs. PL. Moreover, competitive endogenous RNA (ceRNA) network analysis revealed the target binding sites for miRNA such as oar-miR-27a, oar-miR-16b, oar-miR-200a/b/c, oar-miR-181a, oar-miR-10a/b, and oar-miR-432 in the identified DE-cirRNAs.

Comparative Transcriptomics Identify Key Hypothalamic Circular RNAs that Participate in Sheep (Ovis aries) Reproduction

Circular RNA (circRNA), as an emerging class of noncoding RNA, has been found to play key roles in many biological processes. However, its expression profile in the hypothalamus, a powerful organ initiating the reproductive process, has not yet been explored. Therefore, we used RNA sequencing to explore the expression of circRNAs in the hypothalamus of sheep with the FecB ++ genotype. We totally identified 41,863 circRNAs from sheep hypothalamus, in which 333 (162 were upregulated, while 171 were downregulated) were differentially expressed in polytocous sheep in the follicular phase versus monotocous sheep in the follicular phase (PF vs. MF), moreover, 340 circRNAs (163 were upregulated, while 177 were downregulated) were differentially expressed in polytocous sheep in the luteal phase versus monotocous sheep in the luteal sheep (PL vs. ML). We also identified several key circRNAs including oar_circ_0018794, oar_circ_0008291, oar_circ_0015119, oar_circ_0012801, oar_circ_0010234, and oar_circ_0013788 through functional enrichment analysis and oar_circ_0012110 through a competing endogenous RNA network, most of which may participate in reproduction by influencing gonadotropin-releasing hormone (GnRH) activities or affecting key gene expression, indirectly or directly. Our study explored the overall expression profile of circRNAs in sheep hypothalamus, which potentially provides an alternative insight into the mechanism of sheep prolificacy without the effects of FecB mutation.