Key result
Rare miR-499 mutation improves cardiac function vs wild-type in mice by altering mRNA targeting.
Why the study?
The functional consequences of naturally-occurring human myomiR sequence variants on miR-mRNA targeting and cardiac function were unknown.
Does a naturally occurring human miR-499 mutation outside the seed sequence alter cardiac mRNA targeting and function?
Does a naturally occurring human miR-499 mutation outside the seed sequence alter cardiac mRNA targeting and function?
A naturally occurring human miR-499 mutation outside the seed sequence alters mRNA targeting and favorably impacts cardiac function in vivo, highlighting the functional importance of non-seed miR variants.
Hypothesis-generating for non-seed miR-499 variants in cardiac disease; should not yet change clinical practice.
RATIONALE: MyomiRs miR-499, miR-208a and miR-208b direct cardiac myosin gene expression. Sequence complementarity between miRs and their mRNA targets determines miR effects, but the functional consequences of human myomiR sequence variants are unknown. OBJECTIVE: To identify and investigate mutations in human myomiRs in order to better understand how and to what extent naturally-occurring sequence variation can impact miR-mRNA targeting and end-organ function. METHODS AND RESULTS: Screening of ≈2,600 individual DNAs for myomiR sequence variants identified a rare mutation of miR-499, u17c in the 3' end, well outside the seed region thought to determine target recognition. In vitro luciferase reporter analysis showed that the 3' miR-499 mutation altered suppression of a subset of artificial and natural mRNA targets. Cardiac-specific transgenic expression was used to compare consequences of wild-type and mutant miR-499. Both wild-type and mutant miR-499 induced heart failure in mice, but miR-499 c17 misdirected recruitment of a subset of miR-499 target mRNAs to cardiomyocyte RNA-induced silencing complexes, altering steady-state cardiac mRNA and protein make-up and favorably impacting cardiac function. In vitro analysis of miR-499 target site mutations and modeling of binding energies revealed abnormal miR-mRNA duplex configurations induced by the c17 mutation. CONCLUSIONS: A naturally occurring miR-499 mutation outside the critical seed sequence modifies mRNA targeting and end-organ function. This first description of in vivo effects from a natural human miR mutation outside the seed sequence supports comprehensive studies of individual phenotypes or disease-modification conferred by miR mutations.
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Dorn et al. (2012) studied Cardiac function and myomiR sequence variants (n=2,600). miR-499 u17c mutation vs. Wild-type miR-499 was evaluated on mRNA targeting and end-organ function. A rare, naturally occurring miR-499 u17c mutation outside the seed sequence altered mRNA targeting and favorably impacted cardiac function in transgenic mice compared to wild-type miR-499.
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