One of the most long-standing, fundamental mysteries of biology surrounds the poorly understood origins of introns. Introns are segments of noncoding DNA that must be removed from the genetic code before it is translated in the process of making proteins. Introns are an ancient feature found across all eukaryotic life, a wide range of organisms that spans all animals, plants, fungi, and protists, but are absent in prokaryotic genomes such as those of bacteria. There is a massive variation in the number of introns found in different species' genomes, even between closely related species.

Now, a new study led by scientists at UC Santa Cruz and published in the journal Proceedings of the National Academy of Sciences (PNAS) points to introners, one of several proposed mechanisms for the creation of introns discovered in 2009, as an explanation for the origins of most introns across species. The researchers believe that introners are the only likely explanation for intron burst events, in which thousands of introns show up in a genome seemingly all at once, and they find evidence of this in species across the tree of life.

"[This study] provides a plausible explanation for the vast majority of origins of introns," said Russell Corbett-Detig, associate professor of biomolecular engineering and senior author on the study. "There's other mechanisms out there, but this is the only one that I know of that could generate thousands and thousands of introns all at once in the genome. If true, this suggests that we've uncovered a core process driving something that's really special about eukaryotic genomes -- we have these introns, we have genomic complexity."