Gone are the days when microRNAs (miRNAs) were relegated to the unimportant “junk heap” of sequences cluttering up the genome. We now know that these tiny, highly conserved non-coding RNAs play important roles in RNA stability and translation by base-pairing with partially complementary sequences in the 3’ untranslated regions (UTRs) of target mRNAs.
Moreover, a recent paper by Irene Bozzoni and colleagues at the University of Rome posits an important evolutionary role for miRNAs in determining species identity. The researchers observed that the density of miRNA target sites in the 3’ UTRs of orthologous neuronal genes from different species paralleled the species complexity from invertebrates to humans.
In contrast, the density of miRNA target sites in the 3’ UTRs of housekeeping genes did not vary significantly among species. Therefore, Bozzoni and coworkers speculate that genes with complex cellular functions are under selective pressure to acquire miRNA-mediated regulation. RNA Biology, August 2008