title: A heterozygous variant in the human cardiac miR-133 gene, MIR133A2, alters miRNA duplex processing and strand abundance.
abstract: BACKGROUND
  MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate gene expression. Sequential cleavage of miRNA precursors results in a ~22 nucleotide duplex of which one strand, the mature miRNA, is typically loaded into the RNA-induced silencing complex (RISC) while the passenger strand is degraded. Very little is known about how genetic variation might affect miRNA biogenesis and function.
  
  
  RESULTS
  We re-sequenced the MIR1-1, MIR1-2, MIR133A1, MIR133A2, and MIR133B genes, that encode the cardiac-enriched miRNAs, miR-1 and miR-133, in 120 individuals with familial atrial fibrillation and identified 10 variants, including a novel 79T > C MIR133A2 substitution. This variant lies within the duplex at the 3' end of the mature strand, miR-133a-3p, and is predicted to prevent base-pairing and weaken thermostability at this site, favoring incorporation of the passenger strand, miR-133a-5p, into RISC. Genomic DNA fragments containing miR-133a-2 precursor sequences with 79T and 79C alleles were transfected into HeLa cells. On Northern blotting the 79T allele showed strong expression of miR-133a-3p with weak expression of miR-133a-5p. In contrast, the 79C allele had no effect on miR-133a-3p but there was a significant increase (mean 3.6-fold) in miR-133a-5p levels. Deep sequencing of small RNA libraries prepared from normal human and murine atria confirmed that nearly all the mature miR-133a was comprised of miR-133a-3p and that levels of miR-133a-5p were very low. A number of isomiRs with variations at 5' and 3' ends were identified for both miR-133a-3p and miR-133a-5p, with 2 predominant miR-133a-3p isomiRs and one predominant miR-133a-5p isomiR. Bioinformatics analyses indicate that the major miR-133a-3p and 5p isomiRs have numerous predicted target mRNAs, only a few of which are in common.
  
  
  CONCLUSIONS
  Multiple miR-133a isomiRs with potential different mRNA target profiles are present in the atrium in humans and mice. We identified a human 79T > C MIR133A2 variant that alters miRNA processing and results in accumulation of the miR-133a-5p strand that is usually degraded.
authors.affiliation: Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia.
authors.forename: Monique
authors.initials: M
authors.lastname: Ohanian
authors.forename: David T
authors.initials: DT
authors.lastname: Humphreys
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Anderson
authors.forename: Thomas
authors.initials: T
authors.lastname: Preiss
authors.forename: Diane
authors.initials: D
authors.lastname: Fatkin
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000235:genetics*; D014644:Genetic Variation; D006325:Heart Atria / Q000378:metabolism; D006579:Heterozygote; D006801:Humans; D008297:Male; D051379:Mice; D035683:MicroRNAs; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: C544547:MIRN1 microRNA, human; C548234:MIRN133 microRNA, human; D035683:MicroRNAs; C517732:Mirn133 microRNA, mouse; D012333:RNA, Messenger