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MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. miRNAs base-pair to complementary sequences in mRNA molecules, then silence said mRNA molecules by one or more of the following processes:
- Cleavage of the mRNA strand into two pieces,
- Destabilization of the mRNA by shortening its poly(A) tail, or
- Reducing translation of the mRNA into proteins.
The Let-7 microRNA precursor was identified from a study of developmental timing in C. elegans, and was later shown to be part of a much larger class of non-coding RNAs termed microRNAs. miR-98 microRNA precursor from human is a let-7 family member. Let-7 miRNAs have now been predicted or experimentally confirmed in a wide range of species (MIPF0000002). miRNAs are initially transcribed in long transcripts called primary miRNAs (pri-miRNAs), which are processed in the nucleus by Drosha and Pasha to hairpin structures of about 70 nucleotide. These precursors (pre-miRNAs) are exported to the cytoplasm by exportin5, where they are subsequently processed by the enzyme Dicer to a ~22 nucleotide mature miRNA. The involvement of Dicer in miRNA processing demonstrates a relationship with the phenomenon of RNA interference.
The mir-10 microRNA precursor is a short non-coding RNA gene involved in gene regulation. It is part of an RNA gene family which contains mir-10, mir-51, mir-57, mir-99 and mir-100. mir-10, mir-99 and mir-100 have now been predicted or experimentally confirmed in a wide range of species. miR-51 and miR-57 have currently only been identified in the nematode Caenorhabditis elegans.
The miR-16 microRNA precursor family is a group of related small non-coding RNA genes that regulates gene expression. miR-16, miR-15, mir-195 and miR-497 are related microRNA precursor sequences from the mir-15 gene family. This microRNA family appears to be vertebrate specific and its members have been predicted or experimentally validated in a wide range of vertebrate species.
The mir-2 microRNA family includes the microRNA genes mir-2 and mir-13. Mir-2 is widespread in invertebrates, and it is the largest family of microRNAs in the model species Drosophila melanogaster. MicroRNAs from this family are produced from the 3' arm of the precursor hairpin. Leaman et al. showed that the miR-2 family regulates cell survival by translational repression of proapoptotic factors. Based on computational prediction of targets, a role in neural development and maintenance has been suggested.
The miR-92 microRNAs are short single stranded non-protein coding RNA fragments initially discovered incorporated into an RNP complex with a proposed role of processing RNA molecules and further RNP assembly. Mir-92 has been mapped to the human genome as part of a larger cluster at chromosome 13q31.3, where it is 22 nucleotides in length but exists in the genome as part of a longer precursor sequence. There is an exact replica of the mir-92 precursor on the X chromosome. MicroRNAs are endogenous triggers of the RNAi pathway which involves several ribonucleic proteins (RNPs) dedicated to repressing mRNA molecules via translation inhibition and/or induction of mRNA cleavage. miRNAs are themselves matured from their long RNA precursors by ribonucleic proteins as part of a 2 step biogenesis mechanism involving RNA polymerase 2.
Mirtrons are a type of microRNAs that are located in the introns of the mRNA encoding host genes. These short hairpin introns formed via atypical miRNA biogenesis pathways. Mirtrons arise from the spliced-out introns and are known to function in gene expression.
In molecular biology mir-143 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. mir–143 is highly conserved in vertebrates. mir-143 is thought be involved in cardiac morphogenesis but has also been implicated in cancer.
In molecular biology, mir-433 is a short non-coding RNA molecule. MicroRNAs (miRNAs) function as posttranscriptional regulators of expression levels of other genes by several mechanisms. They play roles in development, metabolism and carcinogenesis.
mir-48 microRNA is a microRNA which is found in nematodes, in which it controls developmental timing. It acts in the heterochronic pathway, where it controls the timing of cell fate decisions in the vulva and hypodermis during larval development.
In molecular biology mir-52 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-62 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-84 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-374 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-58 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-71 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-241 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-592 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-652 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms, with expression levels of miRNAs and respective target mRNAs negatively correlated.
In molecular biology mir-3180 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. The mir-10 microRNA precursor is a short non-coding RNA gene that is part of an RNA gene family which contains mir-3180-1, mir-3180-2, mir-3180-3, mir-3180-4 and mir-3180-5. They have now been predicted or experimentally confirmed in a wide range of cancers in humans. mir-3180 has currently only been identified in human Homo sapiens.
References
- ↑ Miska EA, Alvarez-Saavedra E, Abbott AL, Lau NC, Hellman AB, McGonagle SM, et al. (2007). "Most Caenorhabditis elegans microRNAs are individually not essential for development or viability". PLOS Genet. 3 (12): e215. doi: 10.1371/journal.pgen.0030215 . PMC 2134938 . PMID 18085825.
- ↑ Brenner JL, Kemp BJ, Abbott AL (2012). "The mir-51 family of microRNAs functions in diverse regulatory pathways in Caenorhabditis elegans". PLOS ONE. 7 (5): e37185. Bibcode:2012PLoSO...737185B. doi: 10.1371/journal.pone.0037185 . PMC 3353893 . PMID 22615936.
