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
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Cellular localization
Cytoplasmic
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Differential Expression of miR-93 and miR-21 in Granulosa Cells and Follicular Fluid of Polycystic Ovary Syndrome Associating with Different Phenotypes. Naji M et al. (2017) 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.//////////////////
Ovarian function
Early embryo development
Comment
MicroRNA-93 promotes ovarian granulosa cells proliferation through targeting CDKN1A in polycystic ovarian syndrome. Jiang L et al. (2015) Context: MicroRNAs (miRNAs) are small, noncoding RNAs that negatively regulate gene expression post-transcriptionally. Whether differently expressed miRNAs contribute to promoting granulosa cell proliferation in polycystic ovarian syndrome disease (PCOS) remains unknown. Objective: We explored whether certain miRNAs are involved in the ovarian dysfunction of PCOS and the mechanism of increased granulosa cells proliferation. Patients and cells: miRNA expression was analyzed in excised ovarian cortexes from 16 women with PCOS and 8 non-PCOS. An immortalized human granulosa (KGN) cell was used for the mechanism study. Main Outcome Measures: Expressions of miRNAs in ovarian cortexes were measured using qRT-PCR and KGN granulosa cells were cultured for proliferation assays after overexpression or inhibition of miR-93 or after insulin treatment. Bioinformatics were used to identify the potential miRNA targets. Protein expression analysis, luciferase assays and rescue assays were used to confirm the substrate of miR-93. Results: MiR-93 expression was higher in PCOS ovarian cortex and its identified target, CDKN1A, was down-regulated. MiR-93 overexpression promoted cell proliferation and G1 to S transition. Knocking down CDKN1A promoted cell growth and cell cycle progression in granulosa cells, and CDKN1A re-introduction reversed the promotional role of miR-93. High concentrations of insulin induced up-regulation of miR-93, stimulated KGN cells proliferation and reduced CDKN1A expression. Conclusions: miR-93 was increased in PCOS granulosa cells and targeted CDKN1A to promote proliferation and cell cycle progression. Insulin could upregulate the expression of miR-93 and stimulate cell proliferation. This might provide a new insight into the dysfunction of granulosa cells in PCOS./////////////////Human blastocysts exhibit unique microrna profiles in relation to maternal age and chromosome constitution. McCallie BR et al. (2014) To determine microRNA (miRNA) expression in human blastocysts relative to advanced maternal age and chromosome constitution. Cryopreserved human blastocysts were warmed and underwent a trophectoderm biopsy for comprehensive chromosomal screening. Select blastocysts were then lysed, reverse transcribed, and pre-amplified prior to running real-time PCR. Statistical analysis was performed using an internal constant housekeeping miRNA. Significant microRNA's of interest were then analyzed for their predicted genes and biological pathways. Additional cryopreserved blastocysts were warmed and stained for the SIRT1 protein for validation. Human blastocysts exhibit unique miRNA expression profiles in relation to maternal age and chromosome constitution. miR-93 was exclusively expressed in blastocysts from women in their forties and further up-regulated with an abnormal chromosome complement. Up-regulated miR-93 resulted in an inverse down-regulation of targets like SIRT1, resulting in reduced oxidative defense. MiRNAs play an important role in aging as well as chromosome constitution and have downstream effects that regulate proteins which can compromise embryonic development.//////////////////
Expression regulated by
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Ovarian localization
Cumulus
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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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