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. (MIPF0000033, MIPF0000025) miR-51 and miR-57 have currently only been identified in the nematode Caenorhabditis elegans (MIPF0000268, MIPF0000271).
MicroRNAs 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 mature products are thought to have regulatory roles through complementarity to mRNA.
Species distribution
The presence of miR-10 has been detected in a diverse range of bilaterian animals. It is one of the most widely distributed microRNAs in animals, it has been identified in numerous species including human, dog, cat, horse, cow, guinea pig, mouse, rat, common marmoset (Callithrix jacchus), common chimpanzee (Pan troglodytes), rhesus monkey (Macaca mulatta), Sumatran orangutan (Pongo abelii), northern greater galago (Otolemur garnettii), gray short-tailed opossum (Monodelphis domestica), northern treeshrew (Tupaia belangeri), European rabbit (Oryctolagus cuniculus), African bush elephant (Loxodonta africana), nine-banded armadillo (Dasypus novemcinctus), European hedgehog (Erinaceus europaeus), lesser hedgehog tenrec (Echinops telfairi), zebra finch (Taeniopygia guttata), chicken, platypus (Ornithorhynchus anatinus), Western clawed frog (Xenopus tropicalis), Carolina anole (Anolis carolinensis), zebrafish (Danio rerio), Japanese pufferfish (Fugu rubripes), green spotted pufferfish (Tetraodon nigroviridis), Japanese killifish (Oryzias latipes), three-spined stickleback (Gasterosteus aculeatus), Florida lancelet (Branchiostoma floridae), California purple sea urchin (Strongylocentrotus purpuratus), 12 different species of fruit fly (Drosophila), Western honey bee (Apis mellifera), mosquito (Anopheles gambiae), red flour beetle (Tribolium castaneum), the nematode Caenorhabditis elegans, owl limpet (Lottia gigantea), starlet sea anemone (Nematostella vectensis) and the blood fluke Schistosoma japonicum. In some of these species the presence of miR-10 has been shown experimentally, in others the genes encoding miR-10 have been predicted computationally.
Genomic location
The mir-10 genes are found within the Hox gene clusters. In mammals there are four Hox gene clusters, these contain five genes encoding miRNAs (mir-10a, mir-10b, mir-196a-1, mir-196a-2 and mir-196b). The mir-10a gene is located upstream of Hoxb4 and the mir-10b gene is located upstream of Hoxd4. Zebrafish have seven Hox gene clusters, genes encoding miR-10 (mir-10a, mir-10b-1, mir-10b-2 and mir-10c) are found in the Hox Ba, Bb, Ca and Da clusters. A fourth miR-10 gene (mir-10d) is found elsewhere in the genome, at a location homologous to the pufferfish HoxDd cluster.
miR-10*
A miRNA can be derived from each arm of the pre-miRNA hairpin. Historically, the least common of these two miRNA products was denoted by the addition of * to the miRNA name, however the modern convention is to denote mature miRNA products as 5p or 3p. Both mir-10 and mir-10* have been detected in Drosophila. There are many potential targets for miR-10* in Drosophila, including several Hox genes, indicating that miR-10* may also be functional. In Drosophila most mature miR-10 sequences are produced from the 3' arm of the precursor while in the beetle Tribolium castaneum most production comes from the 5' arm. These changes of arm preference during evolution are termed arm switching events, and they are relatively frequent during the evolution of microRNAs.
Pattern of expression
In adult animals, expression of miR-10 is limited to specific organs. The highest levels of miR-10a and miR-10b have been found in the kidneys of mice. Lower levels of miR-10a are seen in small intestine, lung and spleen, and lower levels of miR-10b are seen in skeletal muscle. Expression of miR-10b has also been detected in the ovaries. Adult zebrafish express miR-10a in heart, testis and ovary, and miR-10b in muscle and liver.
In developing embryos, miR-10 is detected at specific stages. Zebrafish embryos show miR-10a expression from 48 to 120 hours post-fertilisation, and miR-10b expression from 12 to 120 hours post-fertilisation. In Drosophila expression of miR-10-3p is highest in 12- to 24-hour-old embryos and in 1st and 3rd instar larvae. Levels of miR-10-5p are highest in 12- to 24-hour-old embryos and much lower in larvae.