Role of intronic promoters. (a) Distribution of Spearman's correlation coefficient between the expression profiles of intragenic miRNAs and their corresponding host genes in the human brain. The gray probability density function (PDF) is for those intragenic miRNAs that are predicted to have an independent intronic promoter in the FANTOM4 brain libraries, while the red PDF is for those miRNAs that are predicted to depend on the promoter of the host gene. (b) Association between miRNA age and presence/absence of an independent promoter. The miRNAs are divided into three age classes according to their conservation in different lineages: vertebrates, mammals and primates. Each bar shows the fraction of intergenic, intronic and host gene promoters in each age class. Old miRNAs (conserved in vertebrates) are enriched in independent intronic promoters compared to the other two classes.
miRNA, microRNA; PDF, probability density function.