Lowly Expressed Human MicroRNA Genes Evolve Rapidly

Abstract

To study the evolution of human microRNAs (miRNAs), we examined nucleotide variation in humans, sequence divergence between species, and genomic clustering patterns for miRNAs with different expression levels. We found that expression level is a major indicator of the rate of evolution and that ∼30% of currently annotated human miRNA genes are almost free of selective pressure.