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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. Most miRNAs are grouped into clusters in the human genome or within families that share functions, expression profiles, promotors, or are incorporated into the same ribonucleic protein. The purpose of having a variety of miRNAs in a single piece of RNA processing machinery is to act as complementary strands to the recognition elements of a variety of target RNA molecules.〔 The recognition elements of target mRNAs are typically within the 3' untranslated regions and with 678 human miRNAs and 472 mouse miRNAs confidently identified so far (miRBASE) there are extensive efforts taking place using bioinformatics tools to scan genomes for potential recognition elements for families of miRNAs in order to identify potential target genes. Mir-92 is no exception and currently identified gene targets have been among those involved in cell cycle regulation and cell signalling, and thus necessary during all stages of mammalian development and essential for the proliferation of cells.〔 miRNAs can be oncogenes or tumor suppressor genes depending on their targets while mir-92 has been implicated as the former in leukaemia forms AML and ALL, Hepatocellular carcinoma (HCC) and several other cancers.〔〔 The search for noninvasive tools for diagnosis and management of cancer is extremely important for reducing the worldwide health burden of cancer. miRNAs show potential as biomarkers and can even be found circulating in the serum. Some circulating miRNAs are specific to tumour patients, while miR-92 on the other-hand is present in healthy individuals in the serum, but levels are variable and appear to change in response to the onset of some cancers.〔 ==Family== miR-92 is part of a large precursor sequence that forms a stem loop once transcribed into RNA. This long precursor sequence is a component of the mir-17-92 cluster which contains 6 additional mir precursor sequences: mir-17, mir-18a, mir-19a, mir-20a and mir19b-1.〔 The components have related functions and also exist in their mature form as part of RNP complexes.〔 The cluster is called Oncomir-1 because all members have been connected with inducing enhanced cell proliferation and suppression of apoptosis.〔 Oncomir-1 has 2 paralogs, miR-106a-363 and mir-106b-25. These are located on different chromosomes and contain individual miRNAs that are highly similar to those encoded by the mir-17-92 cluster. Mir-92-1 for example, appears on the mir-17-92 cluster and mir-92-2 appears on the mir-106a-363 cluster. Because they have identical sequences in their mature form it is not always possible to establish which is prominent in a sample simply by sequencing the small RNA content.〔 The miRNAs of oncomir-1 and its paralogs are likely contribute to tumorigenesis by disregulating critical target genes such as ones involved in apoptosis, proliferation and blocking differentiation or cell cycle exit.〔 The miR-17-92 Cluster has been implicated in Medulloblastoma (MB) which is the most common paediatric malignant brain tumour.〔 It arises when cerebellar granule neurone progenitor (GNP) cells fail to properly migrate and differentiate. MB can be induced by 2 inherited cancer syndromes, one of which is called the Gorlin syndrome and is caused by a mutated PATCHED(PTCH) gene. PTCH is the receptor for Sonic hedgehog (SHH). This SHH signalling pathway is crucial during early development and SSH is the major mitogen for GNP proliferation.〔 Turcots's syndrome can give rise to MB as well, resulting from a mutated adenomatous polyposis coli (APC) gene (a member of the wingless (WNT signalling pathway). But only Gorlin syndrome and the SHH pathway is thought to incorporate the mode of action of the miR-17-92 cluster. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mir-92 microRNA precursor family」の詳細全文を読む スポンサード リンク
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