There's an interesting frontier of microbiology/genetics/biochemistry where microRNAs (this is, of course, miRNA not mRNA (not to be confused with siRNA or RNAi)) are responsible for some functions of fetal development in vertebrate limbs (Harfe 2005). There's a bunch of your DNA that doesn't code for any proteins. So we were all "it's a bunch of junk and no longer functioning, ancient retroviruses!" but then it turns out some of it codes for little snippets of RNA that have affects that are (were?) not well understood. It's not really here nor there but it's interesting enough and it's part of what immunized me against the absolute drivel that comes out of people's mouths when it comes to RNA.