circRNA3669 promotes goat endometrial epithelial cells proliferation via miR-26a/RCN2 to activate PI3K/AKT-mTOR and MAPK pathways

The development of receptive endometrium(RE) from pre-receptive endometrium(PE) for successful embryo implantation is a complex dynamic process in which the morphology and physiological states of the endometrial epithelium undergo a series of significant changes, including cell proliferation and apoptosis. However, the molecular mechanisms are not yet fully understood. In this study, a higher circRNA3669 level was observed in PE than in RE of goats. Functional assays revealed that this overexpression promoted the proliferation of goat endometrial epithelial cells(GEECs) by activating the expression of genes related to the PI3K/AKT-mTOR and MAPK pathways,thereby inhibiting apoptosis in vitro. Furthermore, circRNA3669 functioned as a competing endogenous RNA(ceRNA) to upregulate Reticulocalbin-2(RCN2) expression at the post-transcriptional level by interacting with and downregulating miR-26a in GEECs. In addition, RCN2, which is highly expressed in the PE of goats, was found to be regulated by β-estradiol(E2) and progesterone(P4). Our results demonstrated that RCN2 also affected the key proteins PI3K, AKT, mTOR, JNK, and P38 in the PI3K/AKT-mTOR and MAPK pathways, thereby facilitating GEECs proliferation and suppressing their apoptosis in vitro. Collectively, we constructed a new circRNA3669-miR-26aRCN2 regulatory network in GEECs, which further provides strong evidence that circRNA could potentially play a crucial regulatory role in the development of RE in goats.

Analyses of circRNA profiling during the development from pre-receptive to receptive phases in the goat endometrium

Background: Recent studies have revealed that noncoding RNAs play important regulatory roles in the formation of endometrial receptivity.Circular RNAs(circRNAs) are a universally expressed noncoding RNA species that have been recently proposed to act as miRNA sponges that directly regulate expression of target genes or parental genes.Results: We used Illumina Solexa technology to analyze the expression profiles of circRNAs in the endometrium from three goats at gestational day 5(pre-receptive endometrium,PE) and three goats at gestational day 15(receptive endometrium,RE).Overall,21,813 circRNAs were identified,of which 5,925 circRNAs were specific to the RE and 9,078 were specific to the PE,which suggested high stage-specificity.Further analysis found 334 differentially expressed circRNAs in the RE compared with PE(P < 0.05).The analysis of the circRNA-miRNA interaction network further supported the idea that circRNAs act as miRNA sponges to regulate gene expression.Moreover,some circRNAs were regulated by estrogen(E2)/progesterone(P4) in endometrial epithelium cell lines(EECs) and endometrial stromal cell line(ESCs),and each circRNA molecule exhibited unique regulation characteristics with respect to E2 and P4.Conclusions: These data provide an endometrium circRNA expression atlas corresponding to the biology of the goat receptive endometrium during embryo implantation.