Repression of protein synthesis by miRNAs: how many mechanisms?

MicroRNAs are ∼21-nucleotide-long regulators of gene expression that gain access to their target mRNAs by complementary base pairing. Recent studies have revealed that animal microRNAs might take diverse routes to repress gene expression, affecting both target mRNA levels and translation. Mechanistic details of microRNA-mediated repression are starting to emerge but a comprehensive picture of the inhibition, and particularly the effects on mRNA translation, is still lacking. Recent data support different microRNA mechanisms and a role for cytoplasmic processing bodies in the degradation and storage of mRNAs targeted by microRNA regulators.