Involvement of miRNAs in equine follicle development

Abstract

Previous evidence from in vitro studies suggests specific roles for a subset of miRNAs, including miR-21, miR-23a, miR-145, miR-503, miR-224, miR-383, miR-378, miR-132, and miR-212, in regulating ovarian follicle development. The objective of this study was to determine changes in the levels of these miRNAs in relation to follicle selection, maturation, and ovulation in the monovular equine ovary. In Experiment 1, follicular fluid was aspirated during ovulatory cycles from the dominant (DO) and largest subordinate (S) follicles of an ovulatory wave and the dominant (DA) follicle of a mid-cycle anovulatory wave (nZ6 mares). Follicular fluid levels of progesterone and estradiol were lower (P!0.01) in S follicles than in DO follicles, whereas mean levels of IGF1 were lower (P!0.01) in S and DA follicles than in DO follicles. Relative to DO and DA follicles, S follicles had higher (P%0.01) follicular fluid levels of miR-145 and miR-378. In Experiment 2, follicular fluid and granulosa cells were aspirated from dominant follicles before (DO) and 24 h after (L) administration of an ovulatory dose of hCG (nZ5 mares/group). Relative to DO follicles, L follicles had higher follicular fluid levels of progesterone (PZ0.05) and lower granulosa cell levels of CYP19A1 and LHCGR (P!0.005). Levels of miR-21, miR-132, miR-212, and miR-224 were increased (P!0.05) in L follicles; this was associated with reduced expression of the putative miRNA targets, PTEN, RASA1, and SMAD4. These novel results may indicate a physiological involvement of miR-21, miR-145, miR-224, miR-378, miR-132, and miR-212 in the regulation of cell survival, steroidogenesis, and differentiation during follicle selection and ovulation in the monovular ovary.

MicroRNA-378 regulates oocyte maturation via the suppression of aromatase in porcine cumulus cells

“…In vitro miR-378 overexpression and knockdown experiments revealed that aromatase expression, and therefore, estradiol production, by granulosa cells is posttranscriptionally downregulated by miR-378. These findings were supported by a recent in vivo study showing that miR-378 expression in granulosa cells is dependent on the stage of follicular development and is inversely correlated to the levels of estradiol in the follicular fluid (41). The expression of microRNAs in ovarian cumulus cells has been reported recently (1,35); however, the specific roles in this cell type have only begun to be explored.…”

A miRNA target network putatively involved in follicular atresia

“…Five of the 9 miRNAs confirmed to be upregulated in atretic follicles in the present study (miR-21-5p, miR-21-3p, miR-222, miR-155, and miR-199a-5p) were also found to be increased in subordinate relative to dominant follicles on day 3 of the bovine estrous cycle using deep-sequencing rather than microarray [12]. Another miRNA, miR-378, was previously shown, together with miR-21-5p, to increase in expression in subordinate and anovulatory follicles in horses [13], [14]. Taken together, these results are consistent with an involvement of these miRNAs in follicular atresia in the monovular ovary.…”

MicroRNAs: New Insight in Modulating Follicular Atresia: A Review

“…Among these, miR-142, miR-21, miR-150, miR-21, miR-409a and miR-378 were abundantly expressed in large atretic follicles. Furthermore, miR-378, miR-409a and miR-21 are commonly studied [14,43,44,55,56]; for instance, the role of miR-21 is well characterized in bovines [14] and mice [57] as survival molecules of GCs. Among miRNA families, the profile of the let-7 (lethal-7) miRNA family has been explored across different stages of follicular atresia and it was observed that the expression levels of all let-7 family members were found to be downregulated in healthy and early atretic follicles, while let-7g was highly upregulated in progressively atretic follicles [54].…”

“…Several earlier studies have verified that GC apoptosis plays a pivotal role in follicular atresia and a complex array of molecular mechanisms and regulatory networks are involved in the modulation of GC apoptosis caused by extrinsic and intrinsic factors [7,31,32,33,34,35,36,37,38,39,40]. To date, microarray profiling studies of miRNAs in ovarian tissues and cells have identified large numbers of differentially expressed miRNAs during various follicular developmental processes such as primordial development [18], steroidogenesis [41,42,43], luteal development [16,44], and atresia [45,46,47]. In subsequent target prediction and functional enrichment analysis undertaken to understand their functional involvement, some miRNAs have been categorized in apoptotic pathways.…”