MiR-92a inhibits porcine ovarian granulosa cell apoptosis by targeting Smad7 gene

Oocyte Maturation and miRNAs: Studying a Complicate Interaction to Reveal Possible Biomarkers for Female Infertility

Cellular metabolism, apoptosis, fertilization, and proliferation of granulosa cells belong to a battery of processes where microRNAs can be detected and associated with infertility. The aim of the present review is to focus on mammalian oocyte maturation events and the association between oocyte growth and miRNA expression. PubMed/Medline, Google Scholar and Scopus databases were searched, and 33 studies were included. Regarding the correlation among miRNA expression and the regulation of granulosa cells and cumulus cells, the most important miRNAs were let-7b, let-7c and miR-21. Additionally, the loss of Dicer, an enzyme involved in miRNA biogenesis, is probably a crucial factor in oogenesis, oocyte maturation and embryogenesis. Furthermore, miRNAs interfere with different cellular mechanisms like apoptosis, steroidogenesis, genome integrity, angiogenesis, antioxidative response and, consequently, oocyte maturation. Hence, it is of major importance to clarify the role and mechanism of each miRNA as understanding its action may develop new tools and establish new diagnostic and treatment approaches for infertility and ovarian disorders.

LncRNA SNHG5 adversely governs follicular growth in PCOS via miR-92a-3p/CDKN1C axis

Small nucleolar RNA host genes (SNHGs) have been implicated in various biological processes, yet their involvement in polycystic ovary syndrome (PCOS) remains elusive. Specifically, SNHG5, a long non-coding RNA implicated in several human cancers, shows elevated expression in granulosa cells (GCs) of PCOS women and induces PCOS-like features when overexpressed in mice. In vitro, SNHG5 inhibits GC proliferation and induces apoptosis and cell-cycle arrest at G0/G1 phase, with RNA-seq indicating its impact on DNA replication and repair pathways. Mechanistically, SNHG5 acts as a competing endogenous RNA by binding to miR-92a-3p, leading to increased expression of target gene CDKN1C, which further suppresses GC proliferation and promotes apoptosis. These findings elucidate the crucial role of SNHG5 in the pathogenesis of PCOS and suggest a potential therapeutic target for this condition. Additional investigations such as large-scale clinical studies and functional assays are warranted to validate and expand upon these findings.

miR-6881-3p contributes to diminished ovarian reserve by regulating granulosa cell apoptosis by targeting SMAD4

BACKGROUND

In our previous investigation, we revealed a significant increase in the expression of microRNA-6881-3p (miR-6881-3p) in follicular fluid granulosa cells (GCs) from women with diminished ovarian reserve (DOR) compared to those with normal ovarian reserve (NOR). However, the role of miR-6881-3p in the development of DOR remains poorly understood.

OBJECTIVE

This study aimed to elucidate the involvement of miR-6881-3p in the regulation of granulosa cells (GCs) function and the pathogenesis of DOR.

MATERIALS AND METHODS

Initially, we assessed the expression levels of miR-6881-3p in GCs obtained from human follicular fluid in both NOR and DOR cases and explored the correlation between miR-6881-3p expression and clinical outcomes in assisted reproduction technology (ART). Bioinformatic predictions and dual-luciferase reporter assays were employed to identify the target gene of miR-6881-3p. Manipulation of miR-6881-3p expression was achieved through the transfection of KGN cells with miR-6881-3p mimics, inhibitor, and miRNA negative control (NC). Following transfection, we assessed granulosa cell apoptosis and cell cycle progression via flow cytometry and quantified target gene expression through quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot (WB) analysis. Finally, we examined the correlation between target gene expression levels in GCs from NOR and DOR patients and their association with ART outcomes.

RESULTS

Our findings revealed elevated miR-6881-3p levels in GCs from DOR patients, which negatively correlated with ovarian reserve function and ART outcomes. We identified a direct binding interaction between miR-6881-3p and the 3'-untranslated region of the SMAD4. Transfection with miR-6881-3p mimics induced apoptosis in KGN cell. Furthermore, miR-6881-3p expression negatively correlated with both mRNA and protein levels of the SMAD4. The mRNA and protein levels of SMAD4 were notably reduced in GCs from DOR patients, and SMAD4 mRNA expression positively correlated with ART outcomes. In addition, the mRNA levels of FSHR, CYP11A1 were notably reduced after transfection with miR-6881-3p mimics in KGN cell, while LHCGR notably increased. The mRNA and protein levels of FSHR, CYP11A1 were notably reduced in GCs from DOR patients, while LHCGR notably increased.

CONCLUSION

This study underscores the role of miR-6881-3p in directly targeting SMAD4 mRNA, subsequently diminishing granulosa cell viability and promoting apoptosis, and may affect steroid hormone regulation and gonadotropin signal reception in GCs. These findings contribute to our understanding of the pathogenesis of DOR.

miR-423 sponged by lncRNA NORHA inhibits granulosa cell apoptosis

BACKGROUND

Atresia and degeneration, a follicular developmental fate that reduces female fertility and is triggered by granulosa cell (GC) apoptosis, have been induced by dozens of miRNAs. Here, we report a miRNA, miR-423, that inhibits the initiation of follicular atresia (FA), and early apoptosis of GCs.

RESULTS

We showed that miR-423 was down-regulated during sow FA, and its levels in follicles were negatively correlated with the GC density and the P4/E2 ratio in the follicular fluid in vivo. The in vitro gain-of-function experiments revealed that miR-423 suppresses cell apoptosis, especially early apoptosis in GCs. Mechanically speaking, the miR-423 targets and interacts with the 3'-UTR of the porcine SMAD7 gene, which encodes an apoptosis-inducing factor in GCs, and represses its expression and pro-apoptotic function. Interestingly, FA and the GC apoptosis-related lncRNA NORHA was demonstrated as a ceRNA of miR-423. Additionally, we showed that a single base deletion/insertion in the miR-423 promoter is significantly associated with the number of stillbirths (NSB) trait of sows.

CONCLUSION

These results demonstrate that miR-423 is a small molecule for inhibiting FA initiation and GC early apoptosis, suggesting that treating with miR-423 may be a novel approach for inhibiting FA initiation and improving female fertility.

Identification of microRNAs implicated in modulating resveratrol-induced apoptosis in porcine granulosa cells

MicroRNAs (miRNAs) are small, noncoding RNAs that play a crucial role in the complex and dynamic network that regulates the apoptosis of porcine ovarian granulosa cells (POGCs). Resveratrol (RSV) is a nonflavonoid polyphenol compound that is involved in follicular development and ovulation. In previous study, we established a model of RSV treatment of POGCs, confirming the regulatory effect of RSV in POGCs. To investigate the miRNA-level effects of RSV on POGCs to reveal differentially expressed miRNAs, a control group (n = 3, 0 μM RSV group), a low RSV group (n = 3, 50 μM RSV group), and a high RSV group (n = 3, 100 μM RSV group) were created for small RNA-seq. In total, 113 differentially expressed miRNAs (DE-miRNAs) were identified, and a RT-qPCR analysis showed a correlation with the sequencing data. Functional annotation analysis revealed that DE-miRNAs in the LOW vs. CON group may be involved in cell development, proliferation, and apoptosis. In the HIGH vs. CON group, RSV functions were associated with metabolic processes and responses to stimuli, while the pathways were related to PI3K24, Akt, Wnt, and apoptosis. In addition, we constructed miRNA-mRNA networks related to Apoptosis and Metabolism. Then, ssc-miR-34a and ssc-miR-143-5p were selected as key miRNAs. In conclusion, this study provided an improved understanding of effects of RSV on POGCs apoptosis through the miRNA modulations. The results suggest that RSV may promote POGCs apoptosis by stimulating the miRNA expressions and provided a better understanding of the role of miRNAs combined with RSV in ovarian granulosa cell development in pigs.

Integrated analysis of lncRNA and mRNA for the apoptosis of porcine ovarian granulosa cells after polyphenol resveratrol treatment

Resveratrol (RES) is a non-flavonoid polyphenol compound that can be involved in follicular development and ovulation. However, the mechanism by which resveratrol regulates the apoptosis of porcine ovarian granulosa cells (POGCs) through long non-coding RNA (lncRNA) is poorly understood. We generated POGCs models of different doses of RES (0, 25, 50, 75, and 100 μM). It was observed that the cell viability was the highest in the 50 μM group, and the highest apoptosis rates were recorded in the 100 μM group. Therefore, a control group (n = 3, 0 μM RES group), a low RES group (n = 3, 50 μM RES group), and a high RES group (n = 3, 100 μM RES group) of POGCs were created for next RNA sequencing. Gene Ontology (GO) indicated that differentially expressed lncRNAs associated with apoptotic process were highly enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of lncRNA target genes found that the Wnt signaling pathway and PI3K-Akt signaling pathway were both enriched. Furthermore, we constructed lncRNA-mRNA networks related to Metabolic and Cell Apoptosis, respectively. In the networks, five key-lncRNAs were screened, which may play a significant role in the process of POGCs metabolism and apoptosis. Furthermore, we focused on the function of a lnc-GAM (lncRNA associated with Granulosa cells Apoptosis and Metabolism) and verified that lnc-GAM could influence cell apoptosis in POGCs development by affecting the mRNA expression of apoptosis-related markers, and also affects the secretion of steroid hormones and related genes expression in POGCs cultured in vitro. Our study provides seminal data and important new insights into the regulation of reproductive mechanisms in porcine and other female mammals.

Epigenetic regulation in premature ovarian failure: A literature review

Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a multifactorial and heterogeneous disease characterized by amenorrhea, decreased estrogen levels and increased female gonadotropin levels. The incidence of POF is increasing annually, and POF has become one of the main causes of infertility in women of childbearing age. The etiology and pathogenesis of POF are complex and have not yet been clearly elucidated. In addition to genetic factors, an increasing number of studies have revealed that epigenetic changes play an important role in the occurrence and development of POF. However, we found that very few papers have summarized epigenetic variations in POF, and a systematic analysis of this topic is therefore necessary. In this article, by reviewing and analyzing the most relevant literature in this research field, we expound on the relationship between DNA methylation, histone modification and non-coding RNA expression and the development of POF. We also analyzed how environmental factors affect POF through epigenetic modulation. Additionally, we discuss potential epigenetic biomarkers and epigenetic treatment targets for POF. We anticipate that our paper may provide new therapeutic clues for improving ovarian function and maintaining fertility in POF patients.

CircEML1 facilitates the steroid synthesis in follicular granulosa cells of chicken through sponging gga-miR-449a to release IGF2BP3 expression

Non-coding RNAs (ncRNAs) induced competing endogenous RNAs (ceRNA) play crucial roles in various biological process by regulating target gene expression. However, the studies of ceRNA networks in the regulation of ovarian ovulation processing of chicken remains deficient compared to that in mammals. Our present study revealed that circEML1 was differential expressed in hen's ovarian tissues at different ages (15 W/20 W/30 W/68 W) and identified as a loop structure from EML1 pre-mRNA, which promoted the expressions of CYP19A1/StAR and E2/P4 secretion in follicular granulosa cells (GCs). Furthermore, circEML1 could serve as a sponge of gga-miR-449a and also found that IGF2BP3 was targeted by gga-miR-449a to co-participate in the steroidogenesis, which possibly act the regulatory role via mTOR/p38MAPK pathways. Meanwhile, in the rescue experiment, gga-miR-449a could reverse the promoting role of circEML1 to IGF2BP3 and steroidogenesis. Eventually, this study suggested that circEML1/gga-miR-449a/IGF2BP3 axis exerted an important role in the steroidogenesis in GCs of chicken.

MicroRNA expression in male infertility

Male infertility is a multifactorial disorder that involves different physiopathological mechanisms and multiple genes. In this sense, we analyse the role of miRNAs in this pathology. Gene expression analysis can provide relevant information to detect biomarkers, signalling pathways, pathologic mechanisms, and potential therapeutic targets for the disease. In this review, we describe four miRNA microarrays related to patients who present infertility diseases, including azoospermia, asthenozoospermia, and oligoasthenozoospermic. We selected 13 miRNAs with altered expressions in testis tissue (hsa-miR-122-5p, hsa-miR-145-5p, hsa-miR-16-5p, hsa-miR-193a-3p, hsa-miR-19a-3p, hsa-miR-23a-3p, hsa-miR-30b-5p, hsa-miR-34b-5p, hsa-miR-34c-5p, hsa-miR-374b-5p, hsa-miR-449a, hsa-miR-574-3p and hsa-miR-92a-3p), and systematically examine the mechanisms of four relevant miRNAs (hsa-miR-16-5p, hsa-miR-19a-3p, hsa-miR-92a-3p and hsa-miR-30b-5p) which we found that regulated a large number of proteins. An interaction network was generated, and its connections allowed us to identify signalling pathways and interactions between proteins associated with male infertility. In this way, we confirm that the most affected and relevant pathway is the PI3K-Akt signalling.

Upregulation of miR-33 Exacerbates Heat-Stress-Induced Apoptosis in Granulosa Cell and Follicular Atresia of Nile Tilapia (Oreochromis niloticus) by Targeting TGFβ1I1

High temperature affects egg quality and increases follicular atresia in teleosts. The present study aimed to explore the regulated mechanism of ovary syndrome of Nile tilapia (Oreochromis niloticus) exposed to heat stress. To this end, we conducted histological and biochemical analyses and integrated miRNA-target gene analyses. The histochemical analyses confirmed that heat stress promoted the apoptosis of granulosa cell and therefore resulted in increased follicular atresia in the ovary. Heat stress led to the differential expression of multiple miRNAs (miR-27e, -27b-3p, -33, -34a -133a-5p, and -301b-5p). In a luciferase activity assay, miR-33 bound to the 3′-untranslated region (UTR) of the TGFβ1I1 (transforming growth factor-β1-induced transcript 1) gene and inhibited its expression. A TGFβ1I1 gene signal was detected in the granulosa cells of Nile tilapia by immunohistochemical analysis. Up-regulation of the miR-33 of tilapia at 6 d and 12 d exposed to heat (34.5 °C ± 0.5 °C) had significant down-regulation of the TGFβ1I1 expression of the gene and protein in tilapia ovaries. An miRNA-target gene integrated analysis revealed that miR-33 and TGFβ1I1 function in an apoptosis-related signal pathway. The signal transduction of the vascular endothelial growth factor (VEGF) family members VEGFA and its receptor (KDR) in the heat-stressed group decreased significantly compared with the control group. Transcript-levels of the Bax and Caspase-3 as apoptotic promotors were activated and Bcl-2 and Caspase-8 as apoptotic inhibitors were suppressed in the heat-stressed tilapia. These results suggest that heat stress increases the expression of miR-33, which targets TGFβ1I1 and inhibits its expression, resulting in decreased levels of follicle-stimulating hormone and 17β-estradiol and increased apoptosis by suppressing VEGF signaling, eventually inducing follicular atresia. In conclusion, our results show that the miR-33/TGFβ1I1 axis of Nile tilapia is involved in the follicular development of broodstock, and can suppress VEGF signaling to accelerate follicular atresia. Our findings demonstrate the suppressive role of miR-33 during oocyte development in Nile tilapia.

Discovery of Differentially Expressed MicroRNAs in Porcine Ovaries With Smaller and Larger Litter Size

The number of live births in a litter is an important reproductive trait, and is one of the main indicators which reflect the production level and economic benefit of a pig farm. The ovary is an important reproductive organ of the sow, and it undergoes a series of biological processes during each estrous cycle. A complex transcriptional network containing coding and non-coding RNAs in the ovary closely regulates the reproductive capability of sows. However, the molecular regulation mechanisms affecting sow litter size are still unclear. We investigated the expression profiles of microRNAs (miRNAs) in porcine ovaries from sows with smaller than average litter sizes (SLS) and those with larger litter sizes (LLS). In total, 411 miRNAs were identified, and of these 17 were significantly down-regulated and 16 miRNAs were up-regulated when comparing sows with LLS and SLS, respectively. We further characterized the role of miR-183 which was one of the most up-regulated miRNAs. CCK-8, EdU incorporation and western blotting assays demonstrated that miR-183 promoted the proliferation of granulosa cells (GCs) in pig ovaries. Moreover, miR-183 inhibited the synthesis of estradiol in GCs and promoted the synthesis of progesterone. These results will help in gaining understanding of the role of miRNAs in regulating porcine litter size.

circRNA-Mediated Inhibin-Activin Balance Regulation in Ovarian Granulosa Cell Apoptosis and Follicular Atresia

Ovarian granulosa cells (GC) play an essential role in the development and atresia of follicles. Emerging studies suggest that non-coding RNAs are involved in the regulation of GC apoptosis. Here, we aimed to analyze the function of ssc-circINHA-001, coded by the first exon of the inhibin subunit α gene (INHA), in resisting GC apoptosis and follicular atresia by enhancing the expression of the inhibin subunit β A (INHBA) through a cluster of miRNAs. A higher expression of ssc-circINHA-001 in healthy follicles compared to early atretic follicles was detected by qRT-PCR. Its circular structure was confirmed by RNase R treatment and reversed PCR. The function of ssc-circINHA-001 in GC resistance to apoptosis was detected by in vitro transfection of its si-RNA. Furthermore, the dual-luciferase reporter assay suggested that ssc-circINHA-001 adsorbed three miRNAs, termed miR-214-5p, miR-7144-3p, and miR-9830-5p, which share the common target INHBA. A low expression of ssc-circINHA-001 increased the levels of the free miRNAs, inhibited INHBA expression, and thus raised GCs apoptosis through a shift from the secretion of activin to that of inhibin. Our study demonstrated the existence of a circRNA–microRNAs–INHBA regulatory axis in follicular GC apoptosis and provides insight into the relationship between circRNA function and its coding gene in inhibin/activin balance and ovarian physiological functions.

LncRNA lnc_13814 promotes the cells apoptosis in granulosa cells of duck by acting as apla-miR-145-4 sponge

Follicle development is a vital factor which determines the reproductive performance of poultry. Long noncoding RNAs (lncRNAs) have been reported to maintain animal reproductive function and play key roles in ovarian development and hormone secretion. But the regulatory mechanism of lncRNAs in duck follicle development has seldom been reported. In this study, to better explore the molecular mechanism of follicle development in ducks, the follicular lncRNA was sequenced and analyzed. A total of 9,551 lncRNAs were predicted in the duck follicles. Four hundred and forty-five lncRNAs were differentially expressed between the white follicles and yellow follicles. The results of our studies showed that lnc_13814 promoted cell apoptosis in duck GCs. Furthermore, the bioinformatics analysis results demonstrated that lnc_13814 was involved in a lncRNA-miRNA-mRNA coexpression network and it was observed to sponge two follicle-related miRNAs by a luciferase activity assay. Moreover, we found that overexpression of lnc_13814 significantly increased DNA damage inducible transcript 3 (DDIT3) expression and downregulated GCs apoptosis. Finally, we found that lnc_13814 directly binds to and inhibits apla-mir-145-4; then, lnc_13814 increases the expression of DDIT3 and up-regulates GCs apoptosis. Taken together, our findings demonstrate that lncRNAs have potential effects on duck ovarian follicles and lncRNAs may represent a new approach to understand follicular development.

Identification of small extracellular vesicle subtypes in follicular fluid: Insights into the function and miRNA profiles

The study of small extracellular vesicles (sEVs) heterogeneity is one of the main problems that must be solved, and the different sEV subtypes in follicular fluid are still unclear, limiting our understanding of their function. This study first separated sEV subtypes from follicular fluid using differential ultracentrifugation combined with iodixanol density gradient flotation and then evaluated their miRNA profile and effects on the proliferation and apoptosis of granulosa cells (GCs). We also performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of potential target genes of differentially expressed miRNAs (DEMs) and KEGG analysis of potential target genes of non-DEMs. Low-density sEVs (sEV_F6) were enriched in TSG101, while high-density sEVs (sEV_F8) were enriched in CD63. The miRNA profiles of sEV_F6 and sEV_F8 were heterogeneous, and the differential signaling pathways were mainly related to the adhesion and hypoxic stress pathways, while the same signaling pathways were mainly related to cell proliferation, apoptosis, cell cycle, and autophagy pathways. In addition, the highly expressed miRNAs in both subtypes were mainly related to cell proliferation and apoptosis. Both subtypes transferred their miRNAs into GCs and promoted the proliferation ability of the GCs and inhibited their apoptosis. The results showed for the first time that there are different subtypes of sEVs in follicular fluid and that the miRNA profiles of subtypes are heterogeneous.

High Expression of miR-204 in Chicken Atrophic Ovaries Promotes Granulosa Cell Apoptosis and Inhibits Autophagy

Chicken atrophic ovaries have decreased volume and are indicative of ovarian failure, presence of a tumor, or interrupted ovarian blood supply. Ovarian tumor is accompanied by an increase in follicular atresia, granulosa cell (GC) apoptosis, and autophagy. In a previous study, we found using high throughput sequencing that miR-204 is highly expressed in chicken atrophic ovaries. Thus, in the present study, we further investigated its function in GC apoptosis and autophagy. We found that overexpression of miR-204 reduced mRNA and protein levels of proliferation-related genes and increased apoptosis-related genes. Cell counting kit-8 (CCK-8), 5-ethynyl-2-deoxyuridine (EdU), and flow cytometry assays revealed that miR-204 inhibited GC proliferation and promoted apoptosis. Furthermore, we confirmed with reporter gene assays that Forkhead box K2 (FOXK2) was directly targeted by miR-204. FOXK2, as a downstream regulator of phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signal pathways, promoted GC proliferation and inhibited apoptosis. Subsequently, we observed that miR-204 was involved in GC autophagy by targeting Transient Receptor Potential Melastatin 3 (TRPM3). The luciferase activities of the two binding sites of TRPM3 were decreased in response to treatment with a miR-204 mimic, and the autophagic flux was increased after miR-204 inhibition. However, overexpression of miR-204 had opposite results in autophagosomes and autolysosomes. miR-204 inhibits GC autophagy by suppressing the protein expression of TRPM3/AMP-activated protein kinase (AMPK)/ULK signaling pathway components. Inhibition of miR-204 enhanced autophagy by accumulating and degrading the protein levels of LC3-II (Microtubule Associated Protein Light Chain 3B) and p62 (Protein of 62 kDa), respectively, whereas miR-204 overexpression was associated with contrary results. Immunofluorescence staining showed that there was a significant reduction in the fluorescent intensity of LC3B, whereas p62 protein was increased after TRPM3 silencing. Collectively, our results indicate that miR-204 is highly expressed in chicken atrophic ovaries, which promotes GC apoptosis via repressing FOXK2 through the PI3K/AKT/mTOR pathway and inhibits autophagy by impeding the TRPM3/AMPK/ULK pathway.

MiR-21-5p actions at the Smad7 gene during pig ovarian granulosa cell apoptosis

MicroRNAs (miRNAs) are endogenous non-coding RNAs in eukaryotic cells that modulate apoptosis of ovarian granulosa cells (GCs), which is an important cause of mammalian follicular atresia. In the present study, associations were evaluated between miR-21-5p and the extent of Smad7 protein production in regulation of ovarian granulosa cell (pGC) apoptosis. There was detection of miR-21-5p and Smad7 primarily in the cytoplasm and nucleus of pGCs, respectively. When there was an enhanced abundance of miR-21-5p and decreased abundance of Smad7 there were similar effects in pGCs, including inducing proliferation, inhibiting apoptosis, increasing the number of cells in S and G2/M phases, increasing serum estradiol, and decreasing serum progesterone concentrations. Furthermore, the Smad7 mRNA transcript was identified as a target for miR-21-5p actions, with enhanced abundances of miR-21-5p being associated with a lesser abundance of Smad7 mRNA transcript and protein in pGCs. Overall, results from the present study indicate that miR-21-5p has actions on the Smad7 mRNA transcript during the process of ovarian granulosa cell apoptosis in pigs.

MIR143 Inhibits Steroidogenesis and Induces Apoptosis Repressed by H3K27me3 in Granulosa Cells

The granulosa cell growth factor and apoptotic factor are two factors to determine follicular apoptosis. Whether ssc-miR-143-3p (MIR143) plays as an apoptosis factor in porcine granulosa cells (pGCs) remain unclear. This study tries to investigate what function of MIR143 is and how MIR143 gets these functions in pGCs from 3 to 5 mm medium-sized follicles. Firstly, 5' RACE was used to identify the structure of MIR143, and in situ hybridization, qPCR, and DNA pull-down were employed to exhibit the spatio-temporal expression and transcriptional regulation of MIR143. Furthermore, ELISA, Western blotting, and flow cytometry were adopted to explore the functions of MIR143 in pGCs. It was found that MIR143 was an exonic miRNA located in host gene LOC100514340 with an increasing expression during follicular growth. Moreover, MIR143 suppressed steroidogenesis related genes of HSD17β4, ER1, and PTGS2, negatively regulating estrogen, androgen, progesterone, and prostaglandin. MIR143 induced the apoptosis via activation of BAX-dependent Caspase 3 signaling. Furthermore, H3K27me3 influenced the recruitment of transcription factors and binding proteins to repress MIR143 transcription. At last, H3K27me3 agonist with MIR143 inhibition activated steroidogenesis but repressed apoptosis. These findings suggest that H3K27me3-mediated MIR143 inhibition play a critical role in follicular atresia by regulating cell apoptosis and steroidogenesis, which will provide useful information for further investigations of H3K27me3-miediated MIR143 epigenetic regulation in follicular growth in mammals.

Prediction of major microRNAs in follicular fluid regulating porcine oocyte development

PURPOSE

The aim of the present study was to identify key microRNAs (miRNAs) in porcine follicular fluid (FF) that regulate oocyte growth.

METHODS

miRNAs contained in FF were determined by small RNA-seq of exosome RNA. Upstream regulator miRNA was determined by ingenuity pathway analysis using differentially expressed genes in granulosa cells (GCs) between small follicles (1-2 mm in diameter) and large follicles (3-5 mm), and between follicles containing oocytes of high developmental ability and follicles containing oocytes of low developmental ability. The candidate miRNAs overlapping among the three miRNAs group were determined. Lastly, the effect of supplementation with FF, exosome-depleted FFs, or each miRNA on in vitro oocyte growth was examined.

RESULTS

The miRNAs determined were miR-17, -27, -92a, and -145. These miRNAs were found in the spent culture medium of oocytes and granulosa cells complexes and serum by small RNA sequencing. Culturing of oocytes and granulosa cells complexes collected from porcine early antral follicles (0.5-0.7 mm in diameter) with FF for 14 days improved oocyte growth; depletion of exosomes from the FFs neutralized the beneficial effect observed. miR-92a mimic increased the antrum formation and diameter, together with acetylated levels of H4K12 in oocytes. In addition, supplementation of miRNA mimics miR-17b, -92a, and -145b improved the rate of chromatin configuration, and miR-17b and -92a mimics improved the developmental ability of oocytes to the blastocyst stage.

CONCLUSION

miR-17, -92a, and -145 are major miRNA candidates in follicular fluids regulating oocyte growth.

miRNA-21-3p targeting of FGF2 suppresses autophagy of bovine ovarian granulosa cells through AKT/mTOR pathway

It is widely thought that the main reason for ovarian follicular atresia is apoptosis of granulosa cells, however, accumulating evidence suggests that autophagy plays a role in the fate of granulosa cells. Although epigenetic regulation including miR-21-3p associated with autophagy process has been reported in many cancer types, nevertheless, the mechanism of miR-21-3p in bovine ovary is poorly understood. In the present study, bovine ovarian granulosa cells (BGCs) were used as a model to elucidate the autophagy and role of miR-21-3p in a cattle ovary. The results from gene expression and tagged autophagosomes showed the autophagy in BGCs and miR-21-3p was identified as an important miRNA regulating autophagy of BGCs. The current results indicated that FGF2 was a validated target of miR-21-3p in autophagy regulation of BGCs according to the results from FGF2 luciferase reporter assays and FGF2 overexpression (oe-FGF2) or small interference (si-FGF2). Transfection of miR-21-3p mimic and si-FGF2 plasmids resulted in decreasing phosphorylated AKT and mTOR, while transfection of miR-21-3p inhibitor and oe-FGF2 increased the phosphorylated level of AKT and mTOR in BGCs. These data indicate that regulation of miR-21-3p on BGCs autophagy through AKT/mTOR pathway. In summary, this study suggests that miR-21-3p targets FGF2 to inhibit BGCs autophagy by repressing AKT/mTOR signaling.

The novel fish miRNA pol-miR-novel_171 and its target gene FAM49B play a critical role in apoptosis and bacterial infection

MicroRNAs (miRNAs) are a type of small, non-coding RNAs that participate in many cellular and biological processes by regulating mRNA stability. In a previous study, we identified 96 Japanese flounder (Paralichthys olivaceus) miRNAs responsive to the infection of Edwardsiella tarda, a bacterial pathogen to fish as well as humans. In the current study, we examined the regulation and function of one novel miRNA, i.e., pol-miR-novel_171, from the above 96 miRNA pool. We found that pol-miR-novel_171 expression was regulated by E. tarda and megalocytivirus in a pathogen-specific manner, and that pol-miR-novel_171 targeted the gene of FAM49B (family with sequence similarity 49 member B) of flounder (named PoFAM49B) by negative interaction with the 3'-UTR of PoFAM49B. To date, the function fish FAM49B is unknown. We found that PoFAM49B expressed in multiple tissues of flounder, and recombinant PoFAM49B interacted with and inhibited the growth of Gram-negative bacterial pathogens. Interference with PoFAM49B expression in flounder cells promoted E. tarda infection. Similar effects on E. tarda infection were observed with pol-miR-novel_171 overexpression. Consistently, in vivo knockdown of PoFAM49B in flounder enhanced E. tarda dissemination in fish tissues. Furthermore, interference with PoFAM49B expression, or overexpression of pol-miR-novel_171, promoted apoptosis of flounder cells, while in vitro and in vivo knockdown of PoFAM49B augmented the expressions of key apoptosis-associated genes. These results revealed for the first time the immune function of fish FAM49B and the regulatory mechanism of a novel fish miRNA by demonstrating that pol-miR-novel_171, via PoFAM49B, played a critical role in apoptosis and anti-bacterial immunity.

Transactivation of miR-202-5p by Steroidogenic Factor 1 (SF1) Induces Apoptosis in Goat Granulosa Cells by Targeting TGFβR2

MicroRNAs play key roles during ovary development, with emerging evidence suggesting that miR-202-5p is specifically expressed in female animal gonads. Granulosa cells (GCs) are somatic cells that are closely related to the development of female gametes in mammalian ovaries. However, the biological roles of miR-202-5p in GCs remain unknown. Here, we show that miR-202-5p is specifically expressed in GCs and accumulates in extracellular vesicles (EVs) from large growth follicles in goat ovaries. In vitro assays showed that miR-202-5p induced apoptosis and suppressed the proliferation of goat GCs. We further revealed that miR-202-5p is a functional miRNA that targets the transforming growth factor-beta type II receptor (TGFβR2). MiR-202-5p attenuated TGF-β/SMAD signaling through the degradation of TGFβR2 at both the mRNA and protein level, decreasing p-SMAD3 levels in GCs. Moreover, we verified that steroidogenic factor 1 (SF1) is a transcriptional factor that binds to the promoters of miR-202 and cytochrome P450 family 19 subfamily A member 1 (CYP19A1) through luciferase reporter and chromatin immunoprecipitation (ChIP) assays. That contributed to positive correlation between miR-202-5p and CYP19A1 expression and estradiol (E2) release. Furthermore, SF1 repressed TGFβR2 and p-SMAD3 levels in GCs through the transactivation of miR-202-5p. Taken together, these results suggest a mechanism by which miR-202-5p regulates canonical TGF-β/SMAD signaling through targeting TGFβR2 in GCs. This provides insight into the transcriptional regulation of miR-202 and CYP19A1 during goat ovarian follicular development.

The circular RNA aplacirc_13267 upregulates duck granulosa cell apoptosis by the apla-miR-1-13/THBS1 signaling pathway

Follicle development is a key factor that determines the reproductive performance of poultry. The existing evidence suggests that circular RNAs (circRNAs) play an important role in a variety of biological processes, especially in posttranscriptional regulation, but the regulatory mechanism of circRNAs in duck follicle development has rarely been reported. To better explore the molecular mechanism of follicle development in ducks, we sequenced and analyzed the follicular circRNAs; 4,204 circRNAs were predicted in the duck follicles. Fourteen circRNAs were differentially expressed between the white follicles and yellow follicles. The results of our studies showed that aplacirc_013267 promoted cell apoptosis in duck GCs. Moreover, a bioinformatics prediction analysis demonstrated that aplacirc_013267 was involved in a circRNA-miRNA-mRNA coexpression network and was observed to sponge two follicle-related miRNAs by a luciferase activity assay. Furthermore, we found that overexpression of aplacirc_013267 significantly increased thrombospondin-1 (THBS1) expression and downregulated granulosa cell apoptosis. The mechanistic study showed that aplacirc_013267 directly binds to and inhibits apla-mir-1-13; then, aplacirc_013267 increases the expression of THBS1 and upregulates granulosa cell apoptosis. Taken together, our findings demonstrate that circRNAs have potential effects in duck ovarian follicles and that circRNAs may represent a new avenue to understand follicular development.

The Role of MicroRNAs in Mammalian Fertility: From Gametogenesis to Embryo Implantation

The genetic codes inscribed during two key developmental processes, namely gametogenesis and embryogenesis, are believed to determine subsequent development and survival of adult life. Once the embryo is formed, its further development mainly depends on its intrinsic characteristics, maternal environment (the endometrial receptivity), and the embryo–maternal interactions established during each phase of development. These developmental processes are under strict genetic regulation that could be manifested temporally and spatially depending on the physiological and developmental status of the cell. MicroRNAs (miRNAs), one of the small non-coding classes of RNAs, approximately 19–22 nucleotides in length, are one of the candidates for post-transcriptional developmental regulators. These tiny non-coding RNAs are expressed in ovarian tissue, granulosa cells, testis, oocytes, follicular fluid, and embryos and are implicated in diverse biological processes such as cell-to-cell communication. Moreover, accumulated evidences have also highlighted that miRNAs can be released into the extracellular environment through different mechanisms facilitating intercellular communication. Therefore, understanding miRNAs mediated regulatory mechanisms during gametogenesis and embryogenesis provides further insights about the molecular mechanisms underlying oocyte/sperm formation, early embryo development, and implantation. Thus, this review highlights the role of miRNAs in mammalian gametogenesis and embryogenesis and summarizes recent findings about miRNA-mediated post-transcriptional regulatory mechanisms occurring during early mammalian development.

MicroRNAs regulate granulosa cells apoptosis and follicular development - A review

Objective

MicroRNAs (miRNAs) are the most abundant small RNAs. Approximately 2,000 annotated miRNAs genes have been found to be differentially expressed in ovarian follicles during the follicular development (FD). Many miRNAs exert their regulatory effects on the apoptosis of follicular granulosa cells (FGCs) and FD. However, accurate roles and mechanism of miRNAs regulating apoptosis of FGCs remain undetermined.

Methods

In this review, we summarized the regulatory role of each miRNA or miRNA cluster on FGCs apoptosis and FD on the bases of 41 academic articles retrieved from PubMed and web of science and other databases.

Results

Total of 30 miRNAs and 4 miRNAs clusters in 41 articles were reviewed and summarized in the present article. Twenty nine documents indicated explicitly that 24 miRNAs and miRNAs clusters in 29 articles promoted or induced FGCs apoptosis through their distinctive target genes. The remaining 10 miRNAs and miRNAs of 12 articles inhibited FGCs apoptosis. MiRNAs exerted modulation actions by at least 77 signal pathways during FGCs apoptosis and FD.

Conclusion

We concluded that miRNAs or miRNAs clusters could modulate the apoptosis of GCs (including follicular GCs, mural GCs and cumulus cells) by targeting their specific genes. A great majority of miRNAs show a promoting role on apoptosis of FGCs in mammals. But the accurate mechanism of miRNAs and miRNA clusters has not been well understood. It is necessary to ascertain clearly the role and mechanism of each miRNA or miRNA cluster in the future. Understanding precise functions and mechanisms of miRNAs in FGCs apoptosis and FD will be beneficial in developing new diagnostic and treatment strategies for treating infertility and ovarian diseases in humans and animals.

miR-140 inhibits porcine fetal fibroblasts proliferation by directly targeting type 1 insulin-like growth factor receptor and indirectly inhibiting type 1 insulin-like growth factor receptor expression via SRY-box 4

Objective

This study aimed to elucidate the effect of miR-140 on the proliferation of porcine fetal fibroblasts (PFFs) and identify the target genes of miR-140 in PFFs.

Methods

In this study, bioinformatics software was used to predict and verify target genes of miR-140. Quantitative polymerase chain reaction and western blot were used to detect the relationship between miR-140 and its target genes in PFFs. Dual luciferase reporter gene assays were performed to assess the interactions among miR-140, type 1 insulin-like growth factor receptor (IGF1R), and SRY-box 4 (SOX4). The effect of miR-140 on the proliferation of PFFs was measured by CCK-8 when PFFs were transfected with a miR-140 mimic or inhibitor. The transcription factor SOX4 binding to promoter of IGF1R was detected by chromatin immunoprecipitation assay (ChIP).

Results

miR-140 directly targeted IGF1R and inhibited proliferation of PFFs. Meanwhile, miR-140 targeted transcription factor SOX4 that binds to promoter of porcine IGF1R to indirectly inhibit the expression of IGF1R. In addition, miR-140 inhibitor promoted PFFs proliferation, which is abrogated by SOX4 or IGF1R knockdown.

Conclusion

miR-140 inhibited PFFs proliferation by directly targeting IGF1R and indirectly inhibiting IGF1R expression via SOX4, which play an important role in the development of porcine fetal.

Comparative Identification of MicroRNAs in Apis cerana cerana Workers' Midguts in Responseto Nosema ceranae Invasion

Here, the expression profiles and differentially expressed miRNAs (DEmiRNAs) in the midguts of Apis cerana cerana workers at 7 d and 10 d post-inoculation (dpi) with N. ceranae were investigated via small RNA sequencing and bioinformatics. Five hundred and twenty nine (529) known miRNAs and 25 novel miRNAs were identified in this study, and the expression of 16 predicted miRNAs was confirmed by Stem-loop RT-PCR. A total of 14 DEmiRNAs were detected in the midgut at 7 dpi, including eight up-regulated and six down-regulated miRNAs, while 12 DEmiRNAs were observed in the midgut at 10 dpi, including nine up-regulated and three down-regulated ones. Additionally, five DEmiRNAs were shared, while nine and seven DEmiRNAs were specifically expressed in midguts at 7 dpi and 10 dpi. Gene ontology analysis suggested some DEmiRNAs and corresponding target mRNAs were involved in various functions including immune system processes and response to stimulus. KEGG pathway analysis shed light on the potential functions of some DEmiRNAs in regulating target mRNAs engaged in material and energy metabolisms, cellular immunity and the humoral immune system. Further investigation demonstrated a complex regulation network between DEmiRNAs and their target mRNAs, with miR-598-y, miR-252-y, miR-92-x and miR-3654-y at the center. Our results can facilitate future exploration of the regulatory roles of miRNAs in host responses to N. ceranae, and provide potential candidates for further investigation of the molecular mechanisms underlying eastern honeybee-microsporidian interactions.

MiR-222 inhibits apoptosis in porcine follicular granulosa cells by targeting the THBS1 gene

Apoptosis of granulosa cells affects follicular atresia and reproduction and is regulated by miRNAs and the expression of certain genes. For the present study, we investigated the regulatory relationship between microRNA-222 (miR-222) and THBS1 in porcine follicular granulosa cells (pGCs) and its effects on apoptosis to provide empirical data for developing methods to improve pig fecundity. Results revealed that miR-222 promotes the proliferation of pGCs. MiRNA mimics and luciferase reporter assays revealed that miR-222 functions as an anti-apoptotic factor in pGCs. MiR-222 mimics in pGCs result in the upregulation of the anti-apoptotic BCL-2 gene, down-regulation of the proapoptotic caspase-3 gene, and inhibition of apoptosis. MiR-222 inhibitors reduced BCL-2 and had no significant effect on caspase-3. MiR-222 mimics promoted estrogen levels. Inhibition of THBS1 inhibited pGC apoptosis. Transfection of THBS1-siRNA reduced the proapoptotic BAX gene. MiR-222 can directly target the 3'-untranslated region of the THBS1 gene. MiR-222 mimics suppressed THBS1 mRNA and proteins, but these were upregulated by the miR-222 inhibitor. Transfection of THBS1-siRNA resulted in the inhibition of the miR-222 inhibitor, which suggests that miR-222 inhibits pGC apoptosis by targeting THBS1. These findings suggest that miR-222 and THBS1 play important roles in follicular atresia, ovarian development, and female reproduction.

MicroRNAs in ovarian follicular atresia and granulosa cell apoptosis

MicroRNAs (miRNAs) are short, noncoding RNAs that posttranscriptionally regulate gene expression. In the past decade, studies on miRNAs in ovaries have revealed the key roles of miRNAs in ovarian development and function. In this review, we first introduce the development of follicular atresia research and then summarize genome-wide studies on the ovarian miRNA profiles of different mammalian species. Differentially expressed miRNA profiles during atresia and other biological processes are herein compared. In addition, current knowledge on confirmed functional miRNAs during the follicular atresia process, which is mostly indicated by granulosa cell (GC) apoptosis, is presented. The main miRNA families and clusters, including the let-7 family, miR-23-27-24 cluster, miR-183-96-182 cluster and miR-17-92 cluster, and related pathways that are involved in follicular atresia are thoroughly summarized. A deep understanding of the roles of miRNA networks will not only help elucidate the mechanisms of GC apoptosis, follicular development, atresia and their disorders but also offer new diagnostic and treatment strategies for infertility and other ovarian dysfunctions.

Loss-of-function of sox3 causes follicle development retardation and reduces fecundity in zebrafish

Folliculogenesis is essential for production of female gametes in vertebrates. However, the molecular mechanisms underlying follicle development, particularly apoptosis regulation in ovary, remain elusive. Here, we generated sox3 knockout zebrafish lines using CRISPR/Cas9. sox3 knockout led to follicle development retardation and a reduced fecundity in females. Comparative analysis of transcriptome between sox3^−/− and wild-type ovaries revealed that Sox3 was involved in pathways of ovarian steroidogenesis and apoptosis. Knockout of sox3 promoted follicle apoptosis and obvious apoptosis signals were detected in somatic cells of stages III and IV follicles of sox3^−/− ovaries. Moreover, Sox3 can bind to and activate the promoter of cyp19a1a. Up-regulation of Cyp19a1a expression promoted 17β-estradiol synthesis, which inhibited apoptosis in follicle development. Thus, Sox3 functions as a regulator of Cyp19a1a expression, via 17β-E2 linking apoptosis suppression, which is implicated in improving female fecundity.

Micro-RNAs involved in cellular proliferation have altered expression profiles in granulosa of young women with diminished ovarian reserve

PURPOSE

The study aims to determine differences in micro-RNA (miRNA) expression in granulosa (GC) and cumulus cells (CC) between young women with diminished ovarian reserve (DOR) or normal ovarian reserve (NOR). Secondary objective was to identify downstream signaling pathways that could ultimately indicate causes of lower developmental competence of oocytes from young women with DOR.

METHODS

The method of the study is prospective cohort study.

RESULTS

Of the miRNA, 125 are differentially expressed in GC between DOR and NOR. Only nine miRNA were different in CC; therefore, we focused analysis on GC. In DOR GC, miR-100-5p, miR-16-5p, miR-30a-3p, and miR-193a-3p were significantly downregulated, while miR-155-5p, miR-192-5p, miR-128-3p, miR-486-5p, miR130a-3p, miR-92a-3p, miR-17-3p, miR-221-3p, and miR-175p were increased. This pattern predicted higher cell proliferation in the DOR GC. The primary pathways include MAPK, Wnt, and TGFbeta.

CONCLUSIONS

The miRNA pattern identified critical functions in cell proliferation and survival associated with DOR. GC in women with DOR seems to respond differently to the LH surge.

Regulation and function of runt-related transcription factors (RUNX1 and RUNX2) in goat granulosa cells

Transcription factors, runt-related transcription factor 1 (RUNX1) and 2 (RUNX2), belong to the runt-related (RUNX) gene family and play critical roles in mammalian reproduction processes. However, the regulatory mechanisms of RUNX1 and RUNX2 expression or their functions in goat follicles remain largely unknown. Herein, RUNX1 and RUNX2 proteins were detected in the oocytes and granulosa cells of preantral and antral follicles, as well as corpus luteum by immunohistochemistry. Treatments with human chorionic gonadotropin (hCG) or with the agonists and inhibitors of hCG-induced intracellular signaling pathways in granulosa cells in vitro, we found that hCG increased RUNX1 expression by activating PKC and PI3K signaling molecules, and increased RUNX2 expression by activating adenylate cyclase, PKC, and PI3K signaling molecules. We also demonstrated that miR-181b expression is dependent on the hCG-induced activation of PKC and PKA, and miR-222 expression is dependent on the hCG-induced activation of PI3K and PKC in cultured granulosa cells. Meanwhile, miR-181b and miR-222 suppressed RUNX1 and RUNX2 expression by targeting RUNX1 and RUNX2 3' untranslated regions (3'UTRs) with or without hCG, respectively. These results suggested that hCG-mediated miR-181b and miR-222 expression are important for the regulation of RUNX1 and RUNX2 expression levels in granulosa cells. To explore the specific functions of RUNX1 and RUNX2, we transfected RUNX1 and RUNX2 small interfering RNAs into primary cultured granulosa cells. Knockdown of RUNX1 and RUNX2 significantly decreased progesterone productions and the mRNA abundance of key steroidogenic enzymes (StAR, CYP11A1 and HSD3B) after hCG treatment. But only miR-222 increased estradiol secretion in goat granulosa cells. In addition, knockdown of RUNX1 and RUNX2 also promoted granulosa cell proliferation. The hormonally regulated expression of RUNX1 and RUNX2 in granulosa cells, their involvement in progesterone production, and promoted granulosa cell proliferation suggest important roles of RUNX1 and RUNX2 in follicular development and luteinization.

Discovery and functional characterization of microRNAs and their potential roles for gonadal development in spotted knifejaw, Oplegnathus punctatus

The spotted knifejaw (Oplegnathus punctatus) is a newly emerging economical fishery species in China. Studies focused on the regulation of gonadal development and gametogenesis of spotted knifejaw are still insufficient. As a key post-transcriptional regulator, miRNAs have been shown to play important roles in development and reproduction systems. In this study, small RNA deep sequencing in ovary and testis of spotted knifejaw were performed to screen miRNA expression patterns. After sequencing and bioinformatics analysis, a total of 247 conserved known miRNAs and 41 novel miRNAs were identified in spotted knifejaw gonads for the first time. In addition, 36 miRNAs were differentially expressed between testis and ovary. The putative target genes of differentially expressed (DE) miRNAs were significantly enriched in several pathways related to sexual differentiation and gonadal development, such as steroid hormone biosynthesis. Sequencing data was validated through qRT-PCR analysis of selected DE miRNAs. Dual-luciferase reporter analyses of filtered miRNA-target gene pairs confirmed that opu-miR-27b-3p targeted in piwi2 and mov10l1 3' UTRs and down-regulated their expressions in spotted knifejaw. The notion that mov10l1 and piwi2 enhance germ cells proliferation and regulate gonadal development and gametogenesis suggests that opu-miR-27b-3p may attenuated this process in the gonads of spotted knifejaw. These findings provided insights into regulatory roles of gonadal miRNAs and supplied fundamental resources for further studies on miRNA-mediated post-transcriptional regulation in reproductive system of spotted knifejaw.

MicroRNA-424/503 cluster members regulate bovine granulosa cell proliferation and cell cycle progression by targeting SMAD7 gene through activin signalling pathway

BACKGROUND

The granulosa cells are indispensable for follicular development and its function is orchestrated by several genes, which in turn posttranscriptionally regulated by microRNAs (miRNA). In our previous study, the miRRNA-424/503 cluster was found to be highly abundant in bovine granulosa cells (bGCs) of preovulatory dominant follicle compared to subordinate counterpart at day 19 of the bovine estrous cycle. Other study also indicated the involvement of miR-424/503 cluster in tumour cell resistance to apoptosis suggesting this miRNA cluster may involve in cell survival. However, the role of miR-424/503 cluster in granulosa cell function remains elusive Therefore, this study aimed to investigate the role of miRNA-424/503 cluster in bGCs function using microRNA gain- and loss-of-function approaches.

RESULTS

The role of miR-424/503 cluster members in granulosa cell function was investigated by overexpressing or inhibiting its activity in vitro cultured granulosa cells using miR-424/503 mimic or inhibitor, respectively. Luciferase reporter assay showed that SMAD7 and ACVR2A are the direct targets of the miRNA-424/503 cluster members. In line with this, overexpression of miRNA-424/503 cluster members using its mimic and inhibition of its activity by its inhibitor reduced and increased, respectively the expression of SMAD7 and ACVR2A. Furthermore, flow cytometric analysis indicated that overexpression of miRNA-424/503 cluster members enhanced bGCs proliferation by promoting G1- to S- phase cell cycle transition. Modulation of miRNA-424/503 cluster members tended to increase phosphorylation of SMAD2/3 in the Activin signalling pathway. Moreover, sequence specific knockdown of SMAD7, the target gene of miRNA-424/503 cluster members, using small interfering RNA also revealed similar phenotypic and molecular alterations observed when miRNA-424/503 cluster members were overexpressed. Similarly, to get more insight about the role of miRNA-424/503 cluster members in activin signalling pathway, granulosa cells were treated with activin A. Activin A treatment increased cell proliferation and downregulation of both miRNA-424/503 members and its target gene, indicated the presence of negative feedback loop between activin A and the expression of miRNA-424/503.

CONCLUSION

This study suggests that the miRNA-424/503 cluster members are involved in regulating bovine granulosa cell proliferation and cell cycle progression. Further, miRNA-424/503 cluster members target the SMAD7 and ACVR2A genes which are involved in the activin signalling pathway.

miR-181b-induced SMAD7 downregulation controls granulosa cell apoptosis through TGF-β signaling by interacting with the TGFBR1 promoter

SMAD7 disrupts the TGF-β signaling pathway by influencing TGFBR1 stability and by blocking the binding of TGFBR1 to SMAD2/3. In this study, we showed that SMAD7 attenuated the TGF-β signaling pathway in ovarian granulosa cells (GCs) by regulating TGFBR1 transcriptional activity. To function as a transcription factor, SMAD7 downregulated the mRNA levels of TGFBR1 via direct binding to the SMAD-binding elements (SBEs) within the promoter region of pig TGFBR1. We also showed that SMAD7 enhanced porcine GC apoptosis by interrupting TGFBR1 and the TGF-β signaling pathway. Interestingly, miR-181b, a microRNA that is downregulated during porcine follicular atresia, was identified to be directly targeting SMAD7 at its 3'-UTR. By inhibiting SMAD7, miR-181b could inhibit GC apoptosis by activating the TGF-β signaling pathway. Our findings provide new insights into the mechanisms underlying the regulation of the TGF-β signaling pathway by SMAD7 and miR-181b.

miR-1275 controls granulosa cell apoptosis and estradiol synthesis by impairing LRH-1/CYP19A1 axis

miR-1275 is one of the microRNAs (miRNAs) that are differentially expressed during follicular atresia in pig ovaries, as identified by a miRNA microarray assay in our previous study [1]. However, its functions in follicular atresia remain unknown. In this study, we showed that miR-1275 promotes early apoptosis of porcine granulosa cells (pGCs) and the initiation of follicular atresia, and inhibits E2 release and expression of CYP19A1, the key gene in E2 production. Bioinformatics and luciferase reporter assays revealed that liver receptor homolog (LRH)-1, not CYP19A1, is a direct functional target of miR-1275. In vitro overexpression and knockdown experiments showed that LRH-1 significantly repressed apoptosis and induced E2 secretion and CYP19A1 expression in pGCs. LRH-1, whose expression was regulated by miR-1275, prevented apoptosis in pGCs. Furthermore, luciferase and chromatin immunoprecipitation assays demonstrated that LRH-1 protein bound to the CYP19A1 promoter and increased its activity. Our findings suggest that miR-1275 attenuates LRH-1 expression by directly binding to its 3'UTR. This prevents the interaction of LRH-1 protein with the CYP19A1 promoter, represses E2 synthesis, promotes pGC apoptosis, and initiates follicular atresia in porcine ovaries.

MicroRNAs: tiny molecules with a significant role in mammalian follicular and oocyte development

The genetic regulation of female fertility (follicular development, oocyte maturation and early preimplantation embryo development) involves the spatio-temporal regulation of those genes that play key roles in various stages of the female reproductive axis. MicroRNAs (miRNAs), a class of small non-coding RNAs, are known to regulate the expression of a large proportion of such genes. In recent decades, multiple studies have aimed to determine the roles of these non-coding RNAs in mammalian follicular development, oocyte growth and embryo development. These studies have applied a variety of approaches, including conditional knockout of miRNA biogenesis genes, high-throughput sequencing technologies for pattern recognition in miRNA expression and loss- and gain-of-function of miRNAs in various animal models. In addition to the cellular miRNAs, a large variety of RNAs are found in circulation, being coupled with extracellular vesicles, proteins and lipids. Because of their potential as diagnostic markers for abnormal physiologies, there is increasing interest in the identification of extracellular miRNAs in various biological fluids and spent in vitro culture media. This review focuses on studies addressing the expression and potential role of cellular and extracellular miRNAs in mammalian follicular cell physiology and subsequent ovarian functionality and oocyte maturation.

Differential Expression of miR-93 and miR-21 in Granulosa Cells and Follicular Fluid of Polycystic Ovary Syndrome Associating with Different Phenotypes

The heterogeneous and multifactorial essence of polycystic ovary syndrome (PCOS) renders a remarkable significance to microRNAs (miRNAs). Normo-androgenic (NA) and hyperandrogenic (HA) PCOS patients were compared with matched healthy women. Expression of miRNAs and TGFβ signaling genes was studied by qRT-PCR and western blotting. Effect of androgen on expression of miR-93 and miR-21 and involvement of androgen receptor were appraised. In granulosa cells (GCs), miR-93 and miR-21 showed significantly increased levels in HA patients compared to NA patients. On the contrary, follicular fluid (FF) levels of both miRNAs were significantly decreased in HA group compared to control women. No significant change in the expression of miRNAs in serum samples was detected. Furthermore, mRNA levels of SMAD7 and TGFBR2 were significantly downregulated in GCs of HA group compared to NA and control subjects. TGFBR2 protein level was significantly decreased in HA patients compared to controls. Free testosterone and free androgen index were positively correlated with expression of miR-93 and miR-21 in GCs of PCOS group. Our findings show distinct molecular signature of different subtypes of PCOS. Intermediary position of miRNAs as androgen responsive factors may play critical role in the pathogenesis of PCOS in hyperandrogenic condition.

miR-590 promotes the proliferation of HUMSCs and induces ECM synthesis by targeting Smad7

MicroRNA (miR)-590 has been established to be a promoter of cell proliferation, migration and invasion, and an inhibitor of apoptosis in numerous cancer cell lines. However, its effects on non-cancer cells remain to be elucidated. miR-590 was transfected into human umbilical cord mesenchymal stem cells (HUMSCs), and the cell proliferation rate was determined using a Cell-Light 5-ethynyl-20-deoxyuridine Apollo 567 kit and the presence of extracellular matrix (ECM) proteins were detected using western blot analysis and immunofluorescence microscopy. Using bioinformatic analysis and dual-luciferase assays, the novel target miR-590 was identified. In addition, the effects of miR-590 on cell proliferation and ECM enhancement were also evaluated. The results of the present study demonstrated that miR-590 interacts directly with the 3'-untranslated region of Mothers Against Decapentaplegic Homolog 7 (Smad7), which is an important factor in transforming growth factor-β signaling pathway. Overexpression of miR-590 downregulated Smad7 expression at the mRNA and protein level, and subsequently resulted in cell proliferation and ECM accumulation. Additionally, the transfection of small interfering RNA targeting Smad7 in HUMSCs produced similar effects on cell proliferation and ECM to the overexpression of miR-590. The results of the present study indicated that miR-590 affects HUMSC proliferation by directly targeting Smad7.

Male-biased miR-92 from early chicken embryonic gonads directly targets ATRX and DDX3X

MiR-17-92 cluster consists of multifunctional miRNAs related to gonadal development in mammals. Our preliminary data showed that gga-miR-92 was male-biased in chicken embryonic gonads at E5.5 and E6.5. MiR-92(a-2) and two putative targets (ATRX and DDX3X) were highly conserved and located on mammalian Chromosome X but on autosomes in chicken. Here, we studied the expression and interaction of miR-92 and the targets (ATRX and DDX3X) in chicken embryonic gonads. What's more, male-biased miR-92 shows an opposite expression tendency with ATRX and DDX3X in eight embryonic stages and different tissues at E10.5 by qRT-PCR. To verify the regulation relationship between miR-92 and two targets, we performed dual-luciferase reporter assay in DF1, overexpression and inhibition of miR-92 in chicken embryonic fibroblasts (CEFs). The results show that miR-92 directly targets ATRX and DDX3X by binding the 3' un-translated region (3'-UTR), and the over-expression and inhibition of miR-92 negatively regulates ATRX and DDX3X. After the identification of the expression of their downstream genes (AMH and WNT4) in mRNA level, we found that there is no regulatory relationship between ATRX and DDX3X. The overall results indicate that miR-92 may perform roles in early chicken gonadogenesis by regulating the expressions of ATRX and DDX3X, respectively.

MicroRNAs: New Insight in Modulating Follicular Atresia: A Review

Our understanding of the post-transcriptional mechanisms involved in follicular atresia is limited; however, an important development has been made in understanding the biological regulatory networks responsible for mediating follicular atresia. MicroRNAs have come to be seen as a key regulatory actor in determining cell fate in a wide range of tissues in normal and pathological processes. Profiling studies of miRNAs during follicular atresia and development have identified several putative miRNAs enriched in apoptosis signaling pathways. Subsequent in vitro and/or in vivo studies of granulosa cells have elucidated the functional role of some miRNAs along with their molecular pathways. In particular, the regulatory roles of some miRNAs have been consistently observed during studies of follicular cellular apoptosis. Continued work should gradually lead to better understanding of the role of miRNAs in this field. Ultimately, we expect this understanding will have substantial benefits for fertility management at both the in vivo or/and in vitro levels. The stable nature of miRNA holds remarkable promise in clinical use as a diagnostic tool and in reproductive medicine to solve the ever-increasing fertility problem. In this review, we summarize current knowledge of the involvement of miRNAs in follicular atresia, discuss the challenges for further work and pinpoint areas for future research.

A miRNA target network putatively involved in follicular atresia

In a previous microarray study, we identified a subset of micro RNAS (miRNAs), which expression was distinctly higher in atretic than healthy follicles of cattle. In the present study, we investigated the involvement of those miRNAs in granulosa and theca cells during atresia. Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR) confirmed that miR-21-5p/-3p, miR-150, miR-409a, miR-142-5p, miR-378, miR-222, miR-155, and miR-199a-5p were expressed at higher levels in atretic than healthy follicles (9-17 mm, classified based on steroidogenic capacity). All miRNAs except miR-21-3p and miR-378 were expressed at higher levels in theca than granulosa cells. The expression of 13 predicted miRNA targets was determined in follicular cells by RT-qPCR, revealing downregulation of HIF1A, ETS1, JAG1, VEGFA, and MSH2 in either or both cell types during atresia. Based on increases in miRNA levels simultaneous with decreases in target levels in follicular cells, several predicted miRNA target interactions were confirmed that are putatively involved in follicular atresia, namely miR-199a-5p/miR-155-HIF1A in granulosa cells, miR-155/miR-222-ETS1 in theca cells, miR-199a-5p-JAG1 in theca cells, miR-199a-5p/miR-150/miR-378-VEGFA in granulosa and theca cells, and miR-155-MSH2 in theca cells. These results offer novel insight on the involvement of miRNAs in follicle development by identifying a miRNA target network that is putatively involved in follicle atresia.

TGF-β signaling controls FSHR signaling-reduced ovarian granulosa cell apoptosis through the SMAD4/miR-143 axis

Follicle-stimulating hormone receptor (FSHR) and its intracellular signaling control mammalian follicular development and female infertility. Our previous study showed that FSHR is downregulated during follicular atresia of porcine ovaries. However, its role and regulation in follicular atresia remain unclear. Here, we showed that FSHR knockdown induced porcine granulosa cell (pGC) apoptosis and follicular atresia, and attenuated the levels of intracellular signaling molecules such as PKA, AKT and p-AKT. FSHR was identified as a target of miR-143, a microRNA that was upregulated during porcine follicular atresia. miR-143 enhanced pGC apoptosis by targeting FSHR, and reduced the levels of intracellular signaling molecules. SMAD4, the final molecule in transforming growth factor (TGF)-β signaling, bound to the promoter and induced significant downregulation of miR-143 in vitro and in vivo. Activated TGF-β signaling rescued miR-143-reduced FSHR and intracellular signaling molecules, and miR-143-induced pGC apoptosis. Overall, our findings offer evidence to explain how TGF-β signaling influences and FSHR signaling for regulation of pGC apoptosis and follicular atresia by a specific microRNA, miR-143.

See-Thru-Gonad zebrafish line: developmental and functional validation

Zebrafish are an important model species in developmental biology. However, their potential in reproductive biology research has yet to be realized. In this study, we established See-Thru-Gonad zebrafish, a transparent line with fluorescently labeled germ cells visible throughout the life cycle, validated its gonadal development features, and demonstrated its applicability by performing a targeted gene knockdown experiment using vivo-morpholinos (VMOs). To establish the line, we crossed the zf45Tg and mitfaw2/w2; mpv17b18/b18 zebrafish lines. We documented the in vivo visibility of the germline-specific fluorescent signal throughout development, from gametes through embryonic and juvenile stages up to sexual maturity, and validated gonadal development with histology. We performed targeted gene knockdown of the microRNA (miRNA) miR-92a-3p through injection of VMOs directly to maturing ovaries. After the treatment, zebrafish were bred naturally. Embryos from miR-92a-3p knockdown ovaries had a significant reduction in relative miR-92a-3p expression and a higher percentage of developmental arrest at the 1-cell stage as compared with 5-base mismatch-treated controls. The experiment demonstrates that See-Thru-Gonad line can be successfully used for vertical transmission of the effects of targeted gene knockdown in ovaries into their offspring.

High-throughput sequencing reveals differential expression of miRNAs in prehierarchal follicles of laying and brooding geese

Broodiness is the primary factor influencing egg production in geese, in which several genes and miRNAs participate. Detailed spatiotemporal profiles of miRNAs encompassing follicle development levels, however, are lacking. In this study, we collected preovulatory follicles (classified as small white follicles, large white follicles, and small yellow follicles) from brooding and laying geese and aimed to analyze microRNA (miRNA or miR) during folliculogenesis. High-throughput sequencing and bioinformatics analysis were used to identify the miRNAs involved in follicle development. The let7 family, miR-10 family, and miR-143 family were abundant in these libraries, and they have been suggested to play a housekeeping role during folliculogenesis. Joint comparisons revealed 23 upregulated and 21 downregulated miRNAs (in at least two comparisons of follicles during brooding and laying, P < 0.1) in the laying stage. Unlike reproduction pathways reported for ovaries, GO and KEGG analysis suggested pathways for cell apoptosis and proliferation, such as the regulation of actin cytoskeleton, endocytosis, axon guidance, pathways in cancer, tight junctions, focal adhesion, the MAPK signaling pathway, cytokine-cytokine receptor interactions, and the Wnt signaling pathway in folliculogenesis. This study revealed the miRNAs that were directly involved in follicular atresia, and our results added to the understanding of the functional involvement of miRNAs during specific stages of follicle development.

miR-22 inhibits mouse ovarian granulosa cell apoptosis by targeting SIRT1

Granulosa cell (GC) apoptosis has been shown to be involved in follicular atresia, which is a degenerative process in ovarian follicles of mammals. However, the mechanism underlying the regulation of follicular atresia, particularly by microRNAs, is not well known. Real-time PCR (RT-PCR) was used to detect the expression level of miR-22 in healthy follicles (HF), early atretic follicles (EAF), and progressively atretic follicles (PAF). Flow cytometry was performed to assess the apoptosis of mouse granulosa cells (mGCs) treated with miR-22 mimics or negative control (NC) mimics. Regulation of the expression of SIRT1 by miR-22 was evaluated using a luciferase reporter assay system. To investigate the roles of SIRT1 in mGC apoptosis, the endogenous SIRT1 gene in mGCs was knocked down using an siRNA specific for SIRT1. miR-22 was increased during follicular atresia and suppressed granulosa cell apoptosis. The results of the luciferase reporter assay indicated that SIRT1 was a target gene of miR-22. In addition, knockdown of SIRT1 attenuated apoptosis in mGCs. miR-22 inhibits mGC apoptosis by downregulating SIRT1 directly in vitro. This study provides important insights into understanding the regulation mechanism of ovarian follicle atresia.

Summary: Overexpression of miR-22 inhibits mGC apoptosis by targeting SIRT1, and knockdown of SIRT1 attenuated apoptosis in mGCs. Taken together, these findings provide an improved understanding of the molecular mechanisms of miR-22-mediated follicular development.

MicroRNA in ovarian function

The mammalian ovary is a dynamic organ. The coordination of follicle recruitment, selection, and ovulation and the timely development and regression of the corpus luteum are essential for a functional ovary and fertility. Deregulation of any of these processes results in ovarian dysfunction and potential infertility. MicroRNA (miRNA) are short noncoding RNA that regulate developmental processes and time-sensitive functions. The expression of miRNA in the ovary varies with cell type, function, and stage of the estrous cycle. miRNA are involved in the formation of primordial follicles, follicular recruitment and selection, follicular atresia, oocyte-cumulus cell interaction, granulosal cell function, and luteinization. miRNA are differentially expressed in luteal cells at the various stages of the estrous cycle and during maternal recognition of pregnancy, suggesting a role in luteal development, maintenance, and regression. An understanding of the patterns of expression and functions of miRNA in the ovary will lead to novel therapeutics to treat ovarian dysfunction and improve fertility and, potentially, to the development of better contraceptives.

Hypoxia induces miR-210, leading to anti-apoptosis in ovarian follicular cells of marine medaka Oryzias melastigma

Hypoxia is a major global problem that impairs reproductive functions and reduces the quality and quantity of gametes and the fertilization success of marine fish. Nevertheless, the detailed molecular mechanism underlying hypoxia-induced female reproductive impairment remains largely unknown. There is increasing evidence that miRNA is vital in regulating ovarian functions and is closely associated with female fertility in humans. Certain miRNAs that regulate apoptotic genes can be induced by hypoxia, resulting in cell apoptosis. Using primary ovarian follicular cells of the marine medaka, Oryzias melastigma, as a model, we investigated the response of miR-210 to hypoxic stress in ovarian tissues to see if it would interrupt reproductive functions. A significant induction of miR-210 was found in primary ovarian follicular cells exposed to hypoxia, and gene ontology analysis further highlighted the potential roles of miR-210 in cell proliferation, cell differentiation, and cell apoptosis. A number of miR-210 target apoptotic genes, including Deleted in liver cancer 1 protein (DLC1), STE20-like serine/threonine-protein kinase (SLK), tumor necrosis factor receptor superfamily member 10b (TNFRSF10B), RNA binding motif protein 25 (RBM25), and Ubiquitin-specific-processing protease 7 (USP7), were identified. We further showed that ectopic expression of miR-210 would result in down-regulation of these apoptotic genes. On the other hand, the inhibition of miR-210 promoted apoptotic cell death and the expression of apoptotic marker - caspase 3 in follicular cells under hypoxic treatment, supporting the regulatory role of miR-210 in ovarian cell apoptosis. This study provides new insights on how hypoxia induces miR-210, leading to anti-apoptosis in ovarian follicular cells in fish, which is fundamentally important in environmental sciences and reproductive biology.