Lengthening of 3'UTR Increases Morphological Complexity in Animal Evolution

By analyzing the structure of mRNA transcripts in multiple metazoan species, we observed a striking exponential correlation between the length of 3' untranslated regions (3'UTR) and morphological complexity as measured by the number of cell types in each organism. Cellular diversity was similarly associated with the accumulation of microRNA genes and their putative targets. We propose that the lengthening of 3'UTRs together with a commensurate expansion in post-transcriptional regulation can contribute to the emergence of new cell types during animal evolution.