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 gene silence said mRNA molecules by one or more of the following processes:
- Cleavage of mRNA strand into two pieces,
- Destabilization of mRNA by shortening its poly(A) tail, or
- Translation of mRNA into proteins.
RNA silencing or RNA interference refers to a family of gene silencing effects by which gene expression is negatively regulated by non-coding RNAs such as microRNAs. RNA silencing may also be defined as sequence-specific regulation of gene expression triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are conserved among most eukaryotes. The most common and well-studied example is RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA. Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA).
The miR-8 microRNA precursor, is a short non-coding RNA gene involved in gene regulation. miR-8 in Drosophila melanogaster is expressed from the 3' arm of related precursor hairpins, along with miR-200, miR-236, miR-429 and human and mouse homolog miR-141. Members of this precursor family have now been predicted or experimentally confirmed in a wide range of species. The bounds of the precursors are predicted based on conservation and base pairing and are not generally known.
miR-101 microRNA precursor is a small non-coding RNA that regulates gene expression. Expression of miR-101 has been validated in both human and mouse. This microRNA appears to be specific to the vertebrates and has now been predicted or confirmed in a wide range of vertebrate species. The precursor microRNA is a stem-loop structure of about 70 nucleotides in length that is processed by the Dicer enzyme to form the 21-24 nucleotide mature microRNA. In this case the mature sequence is excised from the 3' arm of the hairpin.
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-124 microRNA precursor is a small non-coding RNA molecule that has been identified in flies, nematode worms, mouse and human. The mature ~21 nucleotide microRNAs are processed from hairpin precursor sequences by the Dicer enzyme, and in this case originates from the 3' arm. miR-124 has been found to be the most abundant microRNA expressed in neuronal cells. Experiments to alter expression of miR-124 in neural cells did not appear to affect differentiation. However these results are controversial since other reports have described a role for miR-124 during neuronal differentiation.
The miR-129 microRNA precursor is a small non-coding RNA molecule that regulates gene expression. This microRNA was first experimentally characterised in mouse and homologues have since been discovered in several other species, such as humans, rats and zebrafish. The mature sequence is excised by the Dicer enzyme from the 5' arm of the hairpin. It was elucidated by Calin et al. that miR-129-1 is located in a fragile site region of the human genome near a specific site, FRA7H in chromosome 7q32, which is a site commonly deleted in many cancers. miR-129-2 is located in 11p11.2.
In molecular biology, miR-130 microRNA precursor is a small non-coding RNA that regulates gene expression. This microRNA has been identified in mouse, and in human. miR-130 appears to be vertebrate-specific miRNA and has now been predicted or experimentally confirmed in a range of vertebrate species. Mature microRNAs are processed from the precursor stem-loop by the Dicer enzyme. In this case, the mature sequence is excised from the 3' arm of the hairpin. It has been found that miR-130 is upregulated in a type of cancer called hepatocellular carcinoma. It has been shown that miR-130a is expressed in the hematopoietic stem/progenitor cell compartment but not in mature blood cells.
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.
The miR-135 microRNA precursor is a small non-coding RNA that is involved in regulating gene expression. It has been shown to be expressed in human, mouse and rat. miR-135 has now been predicted or experimentally confirmed in a wide range of vertebrate species. Precursor microRNAs are ~70 nucleotides in length and are processed by the Dicer enzyme to produce the shorter 21-24 nucleotide mature sequence. In this case the mature sequence is excised from the 5' arm of the hairpin.
In molecular biology, miR-194 microRNA precursor is a small non-coding RNA gene that regulated gene expression. Its expression has been verified in mouse and in human. mir-194 appears to be a vertebrate-specific miRNA and has now been predicted or experimentally confirmed in a range of vertebrate species. The mature microRNA is processed from the longer hairpin precursor by the Dicer enzyme. In this case, the mature sequence is excised from the 5' arm of the hairpin.
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.
There are 89 known sequences today in the microRNA 19 (miR-19) family but it will change quickly. They are found in a large number of vertebrate species. The miR-19 microRNA precursor is a small non-coding RNA molecule that regulates gene expression. Within the human and mouse genome there are three copies of this microRNA that are processed from multiple predicted precursor hairpins:
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.
The miR-29 microRNA precursor, or pre-miRNA, is a small RNA molecule in the shape of a stem-loop or hairpin. Each arm of the hairpin can be processed into one member of a closely related family of short non-coding RNAs that are involved in regulating gene expression. The processed, or "mature" products of the precursor molecule are known as microRNA (miRNA), and have been predicted or confirmed in a wide range of species.
The miR-34 microRNA precursor family are non-coding RNA molecules that, in mammals, give rise to three major mature miRNAs. The miR-34 family members were discovered computationally and later verified experimentally. The precursor miRNA stem-loop is processed in the cytoplasm of the cell, with the predominant miR-34 mature sequence excised from the 5' arm of the hairpin.
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.
miR-138 is a family of microRNA precursors found in animals, including humans. MicroRNAs are typically transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give a ~22 nucleotide product. The excised region or, mature product, of the miR-138 precursor is the microRNA mir-138.
miR-214 is a vertebrate-specific family of microRNA precursors. The ~22 nucleotide mature miRNA sequence is excised from the precursor hairpin by the enzyme Dicer. This sequence then associates with RISC which effects RNA interference.
