AUSTIN, TX — University of Texas at Austin researchers have redefined the adage If at first you don’t succeed, try try again: After nearly half-a-trillion tries molecular scientists witnessed a rare event in the lab that could potentially solve an evolutionary conundrum.
(Article by Tony Cantu)
The find centers on how introns — noncoding sequences of DNA located within genes — embark on the process of multiplying within a genome. Up to now, it’s been an evolutionary puzzle, and the function of introns hasn’t been totally known. An intron is a segment of a DNA or RNA molecule that does not code for proteins and interrupts the sequence of genes.
Humans, for example have more than 200,000 introns that make up about 40 percent of the genome.
In the published paper, Stevens and co-author Sujin Lee, a former UT grad student in cellular and molecular biology, detected losses and gains of introns in developing yeast. The scientific team tested nearly a half-trillion yeast samples and found just two examples in which an intron was added a new gene — a reversal of a splicing reaction.
To make proteins, RNA takes instructions within the DNA to splice the introns out. But in the two instances, the cel allowed spliced-out introns to make it back into a different RNA strand to be recombined back into the genome — thus creating a permanent genetic change, officials said.
This activity is known as intron gains. If they accumulate over time, they can contribute to the development of new species and human disease, said scientists in explaining the real-world implications of a lab finding that could easily be viewed as an abstraction.
“We showed in this project that introns continue to be gained, although infrequently at any point in time,” Stevens said. “But can introns drive evolution? If these sequences give organisms a selective advantage and become fixed in a population, others have shown that it can be a major factor in the creation of new species.”
The finding sheds new light into the creation of diseases such as cancer that emerge with a correlation with the improper removal of introns from RNA, Stevens said.
“We are continuing this work to further understand how this process impacts our genetic history, our future, and the prospects of curing disease.”
“Until now, the only way researchers could track the evolution of introns was through phylogenetic analysis, which is examining the evolutionary relationships among sets of related organisms,” explains Scott Stevens, associate professor of molecular biosciences. “Our work is the first experimental verification that shows how introns can be transposed into an organism.”
The results, published May 23 in the Proceedings of the National Academy of Sciences, address fundamental questions about the evolution of new species. The discovery also could expand understanding of gene expression and the causes of diseases such as cancer, university officials said.
The discovery upends long-held beliefs about certain genetic sequences. Scientists have long known that much of the DNA within any given organism’s genome does not code for functional molecules or protein, university officials explained. But recent research finds such genetic sequences — labeled as “junk” DNA in the scientific nomenclature — possess no functional significance.
But hold the phone; introns are now known to play a role in gene expression. Introns are the portion of gene sequences removed out of RNA before genes are translated into protein.
Take eukaryotes as an example. These are organisms consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus. Eukaryotes are included in the makeup of all living organisms other than the eubacteria and archaebacteria.
When eukaryotes first diverged from bacteria, a massive invasion of introns was introduced into the genome. From yeast to mammals, all living eukaryotes share the common ancestor, scientists explained.
But whereas simple organisms (like the aforementioned yeast) eliminate most of their introns, mammals and other more complex organisms expand their intron inventory, scientists have noted.
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