MicroRNAs: Small regulators with a big impact

MicroRNAs (miRNA) are non-coding small (∼22 nt) RNAs that regulate diverse physiological and developmental processes. In animals, they regulate target genes by binding imperfectly to 3′UTR sequences in mRNAs and attenuate translation. There are hundreds of miRNA genes in animals, and current studies show they constitute a minimum of 1% of known genes. We are just beginning to understand the diverse roles they play in cellular processes, which include signaling pathways, developmental pathways, and possibly various types of cancers.