Introns are “in” right now

REBECA FIGUEROA / COURTESY

UC Davis scientists discover expanded role of introns

Dr. Alan Rose of the College of Biological Sciences, and Jenna Gallegos, graduate student in the Department of Molecular and Cellular Biology, have gleaming evidence that defies long-standing beliefs about the purpose of introns, as well as sheds light on their newfound function in gene expression.

Introns are noncoding pieces of genes that are promptly removed from the genetic sequence during the messenger RNA-building stage in protein production. Students who have taken a general biology course may be under the impression that introns, also known as “junk DNA,” are futile and don’t serve any significant purpose in gene expression.  

“In Intro to Bio, we’re taught that promoters control gene expression, and introns are really only important because they increase genetic diversity,” Gallegos said.  “We now know that introns can play essential roles in the initiation of gene expression. Fine-tuning gene activity is important for everything from protecting plants from drought to producing affordable pharmaceuticals.”

In the Rose Lab, the scientists experimented with a gene called “GUS,” which makes a conspicuous blue pigment when turned on. They fused the GUS gene to a plant gene and then proceeded to delete the promoter. The promoter is essential since it controls gene expression by initiating or preventing transcription of mRNA, or messenger RNA. After deleting the promoter, the scientists expected that gene expression would halt and the blue pigment would no longer be created. To their surprise, the blue pigment continued to be produced as long as the introns remained intact.

“What we found was that the part of a gene thought to control gene expression, the promoter, could be removed with no effect if the gene contained an intron,” Rose said. “This would be like finding that you could take the engine out of a car and it still went just as fast as usual if it had the spare tire in the trunk. Remove the spare tire and the car would not go even if it had an engine.“

These findings about the role that introns play in gene expression can have revolutionary effects in the biotechnology industry. Because biotechnology generally depends on optimal production of desired proteins, introns can help amplify the production of these proteins and create profound change in real world crises.

“This work could benefit humanity by providing a way to boost the productivity of a specific gene in plants and other organisms,” Rose said.  “For example, introns could be used to increase the level of vitamin A in golden rice to reduce the blindness and deaths caused by vitamin A deficiency in third world countries, to boost the levels of vaccine proteins in edible vaccines or to increase plant-based production of pharmaceuticals such as the Zmapp antibodies that were used to treat victims of the recent Ebola outbreak.”

How can researchers then obtain the maximum effect from an intron? The most significant factors are the specific sequence of the intron and its location within the gene. Researchers, being led by Ian Korf, a UC Davis associate professor of molecular and cellular biology at the Genome Center, have collaborated with the Rose Lab to develop a program that predicts the degree to which any intron will affect gene expression. Though more research is necessary in order to gain knowledge of the mysterious process of intron-mediated enhancement, this is definitely a step in the right direction.

“This study really advances our understanding of how introns work and present a new model,” said Judy Callis, a UC Davis professor in the Department of Molecular and Cellular Biology who has also conducted similar research. “It suggests that they have an important role in transcription, which is not what was hypothesized previously.”
Written by: Harnoor Gill — science@theaggie.org