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
Nuclear
Comment
Ovarian function
Follicle atresia
Comment
MiR-106a increases granulosa cell viability and is down-regulated in women with diminished ovarian reserve. Hong L et al. (2018) Women with diminished ovarian reserve (DOR) suffer from reduced fertility, cardiovascular events and osteoporosis. Though differential microRNA (miRNA) expression has been described in several ovarian disorders, little is known about the role of miRNAs in the pathogenesis of DOR. Identify differentially expressed miRNAs in DOR and explore the role of miR-106a in human granulosa cell proliferation. MiRNA microarray (n=3) and RT-qPCR (n=30) were used to examine miRNA expression in serum and granulosa cells from normal cycling and DOR women. Primary human granulosa cells were treated alone or in combination with miR-106a mimic, miR-106a inhibitor, apoptosis signal-regulating kinase 1 (ASK1) siRNA or p38 MAPK inhibitor (SB203580) prior to assessment of cell viability and apoptosis. Western blot was used to measure ASK1 protein and phosphorylation/activation of p38 MAPK. Binding of miR-106a to ASK1 mRNA was examined by 3'UTR luciferase analysis. 15 miRNAs were differentially expressed (n=30) and miR-106a was down-regulated in serum and granulosa cells of DOR women. MiR-106a mimic increased cell viability and attenuated apoptosis, whereas the converse occurred following treatment with miR-106a inhibitor. MiR-106a suppressed ASK1 expression by directly targeting its 3'UTR. MiR-106a inhibitor increased p38 MAPK phosphorylation/activation, and this effect was abolished by treatment with ASK1 siRNA. Whereas knockdown of ASK1 abolished the effects of miR-106a inhibitor on cell viability/apoptosis, pre-treatment with SB203580 did not significantly alter the effects of miR-106a inhibitor. Down-regulation of miR-106a may contribute to the pathogenesis of DOR by reducing granulosa cell viability and promoting apoptosis via enhanced ASK1 signaling.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
MicroRNA expression profile in bovine cumulus-oocyte complexes: Possible role of let-7 and miR-106a in the development of bovine oocytes. Miles JR et al. The objectives of this study included: (1) identify the expression of miRNAs specific to bovine cumulus-oocyte complexes (COCs) during late oogenesis, (2) characterize the expression of candidate miRNAs as well as some miRNA processing genes, and (3) computationally identify and characterize the expression of target mRNAs for candidate miRNAs. Small RNAs in the 16-27bp range were isolated from pooled COCs aspirated from 1- to 10-mm follicles of beef cattle ovaries and used to construct a cDNA library. A total 1798 putative miRNA sequences from the cDNA library of small RNA were compared to known miRNAs. Sixty-four miRNA clusters matched previously reported sequences in the miRBase database and 5 miRNA clusters had not been reported. TaqMan miRNA assays were used to confirm the expression of let-7b, let-7i, and miR-106a from independent collections of COCs. Real-time PCR assays were used to characterize expression of miRNA processing genes and target mRNAs (MYC and WEE1A) for the candidate miRNAs from independent collections of COCs. Expression data were analyzed using general linear model procedures for analysis of variance. The expression of let-7b and let-7i were not different between the cellular populations from various sized follicles. However, miR-106a expression was greater (P<0.01) in oocytes compared with COCs and granulosa cells. Furthermore, all the miRNA processing genes have greater expression (P<0.001) in oocytes compared with COCs and granulosa cells. The expression of potential target mRNAs for let-7 and let-7i (i.e., MYC), and miR-106a (i.e., WEE1A) were decreased (P<0.05) in oocytes compared with COCs and granulosa cells. These results demonstrate specific miRNAs within bovine COCs during late oogenesis and provide some evidence that miRNAs may play a role regulating maternal mRNAs in bovine oocytes.