Overview

A new study proposes introners, one of several proposed mechanisms for the formation of introns (a region that lies within a gene but does not remain in the final mature mRNA molecule following transcription of that gene), as an explanation for the origins of most introns across species.

The science and other stuff to know

Introns are noncoding DNA regions that must be deleted from the genetic code before they can be translated while proteins are made. They are an ancient feature found across all eukaryotic life, which includes all animals, plants, fungi, and protists, but are lacking in prokaryotic genomes such as those of bacteria. The number of introns found in different species’ genomes varies greatly, even among closely related species.

According to an ongoing study published in the journal Proceedings of the National Academy of Sciences by scientists at UC Santa Cruz (UCSC), introners are the only likely explanation for intron burst events. The research team argues that introners can generate thousands of introns in a genome seemingly all at once

“[This study] provides a plausible explanation for the vast majority of origins of introns,” lead author Russell Corbett-Detig said in a press statement. “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 really special about eukaryotic genomes…We have these introns, we have genomic complexity.”

Corbett-Detig and his colleagues came to the conclusion by performing a systematic search and in-depth analysis of intron gain across eukaryotic genomes. The search identified 27,563 introner-derived introns from 548 distinct families, with introners found in 175 (5.2 percent) of studied genomes.

According to the study, marine organisms are 6.5 times more likely to contain introners, and 75 percent of introner-containing marine genomes harbor multiple distinct introner families.

So what?

The proximate and ultimate origins of introns have been a fundamental question in biology. This study demonstrates that introners generate new introns on genomic scales in a remarkable diversity of eukaryotic lineages.

“Despite many similarities, the extensive molecular diversity that underlies Introner transposition reveals that a vast range of transposon families have independently evolved into Introners,” researchers wrote. “In light of these findings, frequent horizontal transfer of “transposable elements (TES)” and the extreme marine biased distribution of species harboring introners, we propose that a crucial factor governing lineages’ tendency to gain introns over time is exposure to transfer of TEs from diverse unrelated eukaryotic organisms.”

This study also indicates susceptibility to acquiring weakly deleterious introners by lateral gene transfer might play the central role in a taxon’s tendency to gain introns.

What’s next?

In future studies, Corbett-Detig and his research team plan to look for proof of horizontal gene transfer in the form of nearly identical introners in two different species.

Corbett-Detig, according to UCSC, has set up data mining pipelines to allow the global community of genomics researchers to contribute new species’ genomes to data repositories. His algorithm will search each new genome’s introners for similarities and compare them to all known introners.