title: How do microRNAs regulate gene expression?
abstract: Several thousand human genes, amounting to about one-third of the whole genome, are potential targets for regulation by the several hundred microRNAs (miRNAs) encoded in the genome. The regulation occurs posttranscriptionally and involves the approximately 21-nucleotide miRNA interacting with a target site in the mRNA that generally has imperfect complementarity to the miRNA. The target sites are almost invariably in the 3'-untranslated region of the messenger RNA (mRNA), often in multiple copies. Metazoan miRNAs were previously thought to down-regulate protein expression by inhibiting target mRNA translation at some stage after the translation initiation step, without much effect on mRNA abundance. However, recent studies have questioned these suppositions. With some targets, an increase in the rate of mRNA degradation by the normal decay pathway contributes to the decrease in protein expression. miRNAs can also inhibit translation initiation, specifically the function of the cap-binding initiation factor, eIF4E. Repressed target mRNAs as well as miRNAs themselves accumulate in cytoplasmic foci known as P-bodies, where many enzymes involved in mRNA degradation are concentrated. However, P-bodies may also serve as repositories for the temporary and reversible storage of untranslated mRNA, and reducing the expression (knockdown) of several distinct P-body protein components can alleviate miRNA-mediated repression of gene expression.
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK. rjj@mole.bio.cam.ac.uk
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Jackson
authors.forename: Nancy
authors.initials: N
authors.lastname: Standart
mesh_terms: D000818:Animals; D001483:Base Sequence; D018387:Codon, Initiator / Q000502:physiology; D015536:Down-Regulation; D039561:Eukaryotic Initiation Factor-4E / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D035683:MicroRNAs / Q000502:physiology*; D008954:Models, Biological; D014176:Protein Biosynthesis / Q000502:physiology; D020871:RNA Stability / Q000502:physiology; D034741:RNA, Small Interfering / Q000502:physiology; D016415:Sequence Alignment
chemical_list: D018387:Codon, Initiator; D039561:Eukaryotic Initiation Factor-4E; D035683:MicroRNAs; D034741:RNA, Small Interfering