The relationship between the evolution of microRNA targets and the length of their UTRs

Background: MicroRNAs (miRNAs) are endogenous small RNA molecules that modulate the gene expression at the post-transcription levels in many eukaryotic cells. Their widespread and important role in animals is gauged by estimates that similar to 25% of all genes are miRNA targets. Results: We perform a systematic investigation of the relationship between miRNA regulation and their targets' evolution in two mammals: human and mouse. We find genes with longer 3' UTRs are regulated by more distinct types of miRNAs. These genes correspondingly tend to have slower evolutionary rates at the protein level. Housekeeping genes are another class of genes that evolve slowly. However, they have a distinctly different type of regulation, with shorter 3' UTRs to avoid miRNA targeting. Conclusion: Our analysis suggests a two-way evolutionary mechanism for miRNA targets on the basis of their cellular roles and the length of their 3' UTRs. Functionally critical genes that are spatially or temporally expressed are stringently regulated by miRNAs. While housekeeping genes, however conserved, are selected to have shorter 3' UTRs to avoid miRNA regulation.