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A microRNA is a small single-stranded non-coding RNA molecule found in plants, animals and some viruses, that functions in RNA silencing and post-transcriptional regulation of gene expression. miRNAs function via base-pairing with complementary sequences within mRNA molecules. As a result, these mRNA molecules are silenced, by one or more of the following processes: (1) Cleavage of the mRNA strand into two pieces, (2) Destabilization of the mRNA through shortening of its poly(A) tail, and (3) Less efficient translation of the mRNA into proteins by ribosomes.
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.
mir-133 is a type of non-coding RNA called a microRNA that was first experimentally characterised in mice. Homologues have since been discovered in several other species including invertebrates such as the fruitfly Drosophila melanogaster. Each species often encodes multiple microRNAs with identical or similar mature sequence. For example, in the human genome there are three known miR-133 genes: miR-133a-1, miR-133a-2 and miR-133b found on chromosomes 18, 20 and 6 respectively. The mature sequence is excised from the 3' arm of the hairpin. miR-133 is expressed in muscle tissue and appears to repress the expression of non-muscle genes.
miR-196 is a non-coding RNA called a microRNA that has been shown to be expressed in humans and mice. miR-196 appears to be a vertebrate specific microRNA and has now been predicted or experimentally confirmed in a wide range of vertebrate species. In many species the miRNA appears to be expressed from intergenic regions in HOX gene clusters. The hairpin precursors are predicted based on base pairing and cross-species conservation—their extents are not known. In this case the mature sequence is excised from the 5' arm of the hairpin.
The miR-199 microRNA precursor is a short non-coding RNA gene involved in gene regulation. miR-199 genes have now been predicted or experimentally confirmed in mouse, human and a further 21 other species. microRNAs are transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give a ~22 nucleotide product. The mature products are thought to have regulatory roles through complementarity to mRNA.
The miR-1 microRNA precursor is a small micro RNA that regulates its target protein's expression in the cell. microRNAs are transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give products at ~22 nucleotides. In this case the mature sequence comes from the 3' arm of the precursor. The mature products are thought to have regulatory roles through complementarity to mRNA. In humans there are two distinct microRNAs that share an identical mature sequence, these are called miR-1-1 and miR-1-2.
In molecular biology, the microRNA miR-219 was predicted in vertebrates by conservation between human, mouse and pufferfish and cloned in pufferfish. It was later predicted and confirmed experimentally in Drosophila. Homologs of miR-219 have since been predicted or experimentally confirmed in a wide range of species, including the platyhelminth Schmidtea mediterranea, several arthropod species and a wide range of vertebrates. The hairpin precursors are predicted based on base pairing and cross-species conservation; their extents are not known. In this case, the mature sequence is excised from the 5' arm of the hairpin.
This family represents the microRNA (miRNA) precursor mir-7. This miRNA has been predicted or experimentally confirmed in a wide range of species. miRNAs are transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give a ~22 nucleotide product. In this case the mature sequence comes from the 5' arm of the precursor. The extents of the hairpin precursors are not generally known and are estimated based on hairpin prediction. The involvement of Dicer in miRNA processing suggests a relationship with the phenomenon of RNA interference.
MiR-155 is a microRNA that in humans is encoded by the MIR155 host gene or MIR155HG. MiR-155 plays a role in various physiological and pathological processes. Exogenous molecular control in vivo of miR-155 expression may inhibit malignant growth, viral infections, and enhance the progression of cardiovascular diseases.
In molecular biology mir-126 is a short non-coding RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several pre- and post-transcription mechanisms.
In molecular biology, miR-137 is a short non-coding RNA molecule that functions to regulate the expression levels of other genes by various mechanisms. miR-137 is located on human chromosome 1p22 and has been implicated to act as a tumor suppressor in several cancer types including colorectal cancer, squamous cell carcinoma and melanoma via cell cycle control.
In molecular biology mir-22 microRNA is a short RNA molecule. MicroRNAs are an abundant class of molecules, approximately 22 nucleotides in length, which can post-transcriptionally regulate gene expression by binding to the 3' UTR of mRNAs expressed in a cell.
In molecular biology MicroRNA-223 (miR-223) is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. miR-223 is a hematopoietic specific microRNA with crucial functions in myeloid lineage development. It plays an essential role in promoting granulocytic differentiation while also being associated with the suppression of erythrocytic differentiation. miR-223 is commonly repressed in hepatocellular carcinoma and leukemia. Higher expression levels of miRNA-223 are associated with extranodal marginal-zone lymphoma of mucosa-associated lymphoid tissue of the stomach and recurrent ovarian cancer. In some cancers the microRNA-223 down-regulation is correlated with higher tumor burden, disease aggressiveness, and poor prognostic factors. MicroRNA-223 is also associated with rheumatoid arthritis, sepsis, type 2 diabetes, and hepatic ischemia.
MicroRNA 146a is a small non-coding RNA that in humans is encoded by the MIR146A gene.
In molecular biology mir-363 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-198 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-802 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-939 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-398 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
