Motivation: MicroRNAs (miRNAs) are involved in an abundant class of post-transcriptional regulation activated through binding to the 3(') -untranslated region (UTR) of mRNAs. The current wealth of mammalian miRNA genes results mostly from genomic duplication events. Many of these events are located within introns of transcriptional units. In order to better understand the genomic expansion of miRNA genes, we investigated the distribution of intronic miRNAs.
Results: We observe that miRNA genes are hosted within introns of short genes much larger than expected by chance.
Implementation: We explore several explanations for this phenomenon and conclude that miRNA integration into short genes might be evolutionary favorable due to interaction with the pre-mRNA splicing mechanism.