Abundance of microRNA target motifs in the 3'-UTRs of 20527 human genes.

A mechanism, selective avoidance, proposes that microRNA (miRNA) target sites are selectively depleted in the 3'-UTRs of genes expressed at the same time and place as a miRNA. If this mechanism is ubiquitous, the target motif occurrences in the 3'-UTRs would be decreased. To test this hypothesis, we examined miRNA target motif occurrences in the 3'- and 5'-UTRs of 20527 human protein-coding genes. The results revealed that miRNA target motifs appeared more frequently than non-target motifs and were enriched in the 3'-UTRs. This enrichment was relatively reduced in a set of 2525 genes coexpressed with miR-124a in the prefrontal cortex, but still remained at a high level, suggesting that miRNA target motifs are fostered by some other factors that surpass the influence of selective avoidance.