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WormBook
2005[Sep]; ? (?): 1-9
PMID18050425
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MicroRNAs (miRNAs) are small, non-coding regulatory RNAs found in many phyla that
control such diverse events as development, metabolism, cell fate and cell death.
They have also been implicated in human cancers. The C. elegans genome encodes
hundreds of miRNAs, including the founding members of the miRNA family lin-4 and
let-7. Despite the abundance of C. elegans miRNAs, few miRNA targets are known
and little is known about the mechanism by which they function. However, C.
elegans research continues to push the boundaries of discovery in this area.
lin-4 and let-7 are the best understood miRNAs. They control the timing of adult
cell fate determination in hypodermal cells by binding to partially complementary
sites in the mRNA of key developmental regulators to repress protein expression.
For example, lin-4 is predicted to bind to seven sites in the lin-14 3'
untranslated region (UTR) to repress LIN-14, while let-7 is predicted to bind two
let-7 complementary sites in the lin-41 3' UTR to down-regulate LIN-41. Two other
miRNAs, lsy-6 and mir-273, control left-right asymmetry in neural development,
and also target key developmental regulators for repression. Approximately one
third of the C. elegans miRNAs are differentially expressed during development
indicating a major role for miRNAs in C. elegans development. Given the
remarkable conservation of developmental mechanism across phylogeny, many of the
principles of miRNAs discovered in C. elegans are likely to be applicable to
higher animals.
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