NCBI Summary:
microRNAs (miRNAs) are short (20-24 nt) non-coding RNAs that are involved in post-transcriptional regulation of gene expression in multicellular organisms by affecting both the stability and translation of mRNAs. miRNAs are transcribed by RNA polymerase II as part of capped and polyadenylated primary transcripts (pri-miRNAs) that can be either protein-coding or non-coding. The primary transcript is cleaved by the Drosha ribonuclease III enzyme to produce an approximately 70-nt stem-loop precursor miRNA (pre-miRNA), which is further cleaved by the cytoplasmic Dicer ribonuclease to generate the mature miRNA and antisense miRNA star (miRNA*) products. The mature miRNA is incorporated into a RNA-induced silencing complex (RISC), which recognizes target mRNAs through imperfect base pairing with the miRNA and most commonly results in translational inhibition or destabilization of the target mRNA. The RefSeq represents the predicted microRNA stem-loop. [provided by RefSeq, Sep 2009]
General function
RNA processing
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Antral follicle growth, Follicle atresia
Comment
Conserved miR-10 family represses proliferation and induces apoptosis in ovarian granulosa cells. Jiajie T et al. (2017) Granulosa cells (GCs) are essential somatic cells in the ovary and play an important role in folliculogenesis. Brain-derived neurotropic factor (BDNF) and the TGF-β pathway have been identified as a critical hormone and signalling pathway, respectively, in GCs. In this study, we found that a conserved microRNA family that includes miR-10a and miR-10b repressed proliferation and induced apoptosis in human, mouse, and rat GCs (hGCs, mGCs and rGCs, respectively). Moreover, essential hormones and growth factors in the follicle, such as FSH, FGF9 and some ligands in the TGF-β pathway (TGFβ1, Activin A, BMP4 and BMP15), inhibited miR-10a and miR-10b expression in GCs. In contrast, the miR-10 family suppressed many key genes in the TGF-β pathway, suggesting a negative feedback loop between the miR-10 family and the TGF-β pathway in GCs. By using bioinformatics approaches, RNA-seq, qPCR, FISH, immunofluorescence, Western blot and luciferase reporter assays, BDNF was identified as a direct target of the miR-10 family in GCs. Additionally, reintroduction of BDNF rescued the effects of miR-10a and miR-10b in GCs. Collectively, miR-10a and miR-10b repressed GC development during folliculogenesis by repressing BDNF and the TGF-β pathway. These effects by the miR-10 family on GCs are conserved among different species.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
MicroRNAs: new candidates for the regulation of the human cumulus-oocyte complex. Assou S 2013 et al.
STUDY QUESTION
What is the expression pattern of microRNAs (miRNAs) in human cumulus-oocyte complexes (COCs)?
SUMMARY ANSWER
Several miRNAs are enriched in cumulus cells (CCs) or oocytes, and are predicted to target genes involved in biological functions of the COC.
WHAT IS KNOWN ALREADY
The transcriptional profiles of human MII oocytes and the surrounding CCs are known. However, very limited data are available about post-transcriptional regulators, such as miRNAs. This is the first study focussing on the identification and quantification of small RNAs, including miRNAs, in human oocytes and CCs using a deep-sequencing approach.
STUDY DESIGN, SIZE, DURATION
MII oocytes and CCs were collected from women who underwent IVF.
PARTICIPANTS/MATERIALS, SETTING, METHODS
Using the Illumina/deep-sequencing technology, we analyzed the small RNAome of pooled MII oocytes (n = 24) and CC samples (n = 20). The mRNA targets of CC and MII oocyte miRNAs were identified using in silico prediction algorithms. Using oligonucleotide microarrays, genome-wide gene expression was studied in oocytes (10 pools of 19 3 oocytes/each) and 10 individual CC samples. TaqMan miRNA assays were used to confirm the sequencing results in independent pools of MII oocytes (3 pools of 8 3 oocytes/each) and CC samples (3 pools of 7 3 CCs/each). The functional role of one miRNA, MIR23a, was assessed in primary cultures of human CCs.
MAIN RESULTS AND THE ROLE OF CHANCE
Deep sequencing of small RNAs yielded more than 1 million raw reads. By mapping reads with a single location to the human genome, known miRNAs that were abundant in MII oocytes (MIR184, MIR100 and MIR10A) or CCs (MIR29a, MIR30d, MIR21, MIR93, MIR320a, MIR125a and the LET7 family) were identified. Predicted target genes of the oocyte miRNAs were associated with the regulation of transcription and cell cycle, whereas genes targeted by CC miRNAs were involved in extracellular matrix and apoptosis. Comparison of the predicted miRNA target genes and mRNA microarray data resulted in a list of 224 target genes that were differentially expressed in MII oocytes and CCs, including PTGS2, CTGF and BMPR1B that are important for cumulus-oocyte communication. Functional analysis using primary CC cultures revealed that BCL2 and CYP19A1 mRNA levels were decreased upon MIR23a overexpression.
LIMITATIONS, REASONS FOR CAUTION
Only known miRNAs were investigated in the present study on COCs. Moreover, the source of the material is MII oocytes that failed to fertilize.
WIDER IMPLICATIONS OF THE FINDINGS
The present findings suggest that miRNA could play a role in the regulation of the oocyte and CC crosstalk.
STUDY FUNDING/COMPETING INTEREST(S)
This work was partially supported by a grant from Ferring Pharmaceuticals. The authors of the study have no conflict of interest to report.
TRIAL REGISTRATION NUMBER
Not applicable.
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