Age of miRNA families relative to their expression levels and numbers of predicted target genes. (A) Expression level distributions of miRNA families of different ages. Expression values for each miRNA family were computed as the median expression levels of all family members across all tissues. Also, common expression values associated with two or more miRNA loci with highly similar mature sequences were divided by the number of loci involved. Age categories of miRNA families are represented from the most recent (far left) to the most ancient (far right) for each species based on their phylogenetic distribution (see Methods). (B) Number of predicted target genes of miRNA families of different ages divided by the number of predicted targets for mock miRNAs from random intronic sequences (Methods) using PITA. Number of target genes per miRNA family was computed as the median number of targets of all family members. (C) Evolution of mature miRNA sequences. The percentage of miRNA families displaying one or more modifications in the mature sequence (substitutions in the seed or in the rest of the mature sequence; shifts in the 5′ or 3′ end of the mature miRNA) is shown together with 95% confidence intervals.
