Featured Research

from universities, journals, and other organizations

How Gene Function Drives Natural Selection In Important Class Of Genetic Elements

Date:
December 24, 2008
Source:
University of Georgia
Summary:
For years, researchers thought that most of DNA was passive "junk" and knew little about it. However, new findings are peeling back the odd and baffling world of transposons. Now, researchers have just found that natural selection on gene function is driving the evolution of one kind of transposable element called the LTR retrotransposon.

Regina Baucom, genetics post-doctoral research assistant at UGA and lead author of the research.
Credit: University of Georgia

Transposons are the Clark Kents of a genome. Apparently mild-mannered and inconsequential but with sudden bursts of activity, these free-floating bits of genetic material have for millions of years been sneaking into the genetic maps of plants and animals, dramatically increasing a genome's size.

Related Articles


For years, researchers thought that most of this DNA was passive "junk" and knew little about it. New findings, however, are peeling back the odd and baffling world of transposons. Now, researchers at the University of Georgia have just found that natural selection on gene function is driving the evolution of one kind of transposable element called the LTR retrotransposon. (LTR refers to the "long terminal repeat"—a repetition of a recognizable sequence of nucleotides, the chemical bases that make up strands of DNA.)

"The lab of Professor Jeff Bennetzen at UGA discovered that this class of mobile DNA comprises more than half of most plant genomes and has led the way in determining the extraordinary rates of both amplification and removal of this type of repetitive element," said Regina Baucom, a genetics post-doctoral research assistant at UGA and lead author of the research.

Understanding the evolutionary pressures between host genome and transposable element will in the future be of interest to those studying retroviruses, which evolved from retrotransposons. There are a number of animal and human diseases caused by retroviruses including HIV/AIDS, avian leukosis and feline leukemia.

"Because LTR retrotransposons are abundant and impact host genomes, we wanted to determine the influence of natural selection on their evolution," said Baucom. "We find that the genes involved in their replication are subject to Darwinian evolution—the same evolutionary processes that affect species."

Other authors of the paper just published in the online version of the journal Genome Research, were Jeff Bennetzen, in whose genetics lab Baucom is a research associate; and James Estill and Jim Leebens-Mack in UGA's department of plant biology.

A "retrotransposon" is an element that copies itself and then pastes copies back into genomes at multiple places. It does this by initially copying itself into RNA, but this RNA element is then copied into DNA by an enzyme called reverse transcriptase.

"In this study, we specifically wanted to assess the pattern of selection on these elements—a pattern that could derive from the effect of the elements on the host genome, or the effect of host silencing mechanisms on the elements," Baucom said. "Our expectation was that if the elements are adapting to the host genome, we should see evidence of positive selection in the genes involved in transposition."

The researchers examined selection pressure on retrotransposons using Oryza sativa—rice—as a model plant genome. They analyzed more than 1,000 LTR retrotransposon sequences from 14 separate families that varied in both the dates they were inserted into the rice genome and the numbers of copies that were inserted.

"Overwhelmingly, we found that LTR retrotransposons are under significant evolutionary constraint, by finding strong purifying selection on genes involved in their replication and life-cycle, regardless of the family that any the LTR retrotransposon sequences might belong," says Baucom.

This evidence of so-called "purifying selection" across all gene regions is important in understanding how retrotransposons work. But the research also shows there are rare episodes of positive selection and even adaption to a host genome when these Clark Kents get busy.

It has been known for a long time that the insertion of transposable elements can harm the host, but few studies have been done to determine if there is evidence of selection pressure on LTR retrotransposons.

What the scientists found helps explain why these elements can, while lying quiet for millions of years, suddenly amplify within genomes while not causing more long-term harm than to take up space. And yet the observation that a tiny percentage of the elements actually become active parts of genomes provides an intriguing glimpse into how these twin evolutionary pressures can, in rare cases, "sign an armistice."

The research was supported principally by grants from the National Science Foundation.


Story Source:

The above story is based on materials provided by University of Georgia. Note: Materials may be edited for content and length.


Cite This Page:

University of Georgia. "How Gene Function Drives Natural Selection In Important Class Of Genetic Elements." ScienceDaily. ScienceDaily, 24 December 2008. <www.sciencedaily.com/releases/2008/12/081210121922.htm>.
University of Georgia. (2008, December 24). How Gene Function Drives Natural Selection In Important Class Of Genetic Elements. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2008/12/081210121922.htm
University of Georgia. "How Gene Function Drives Natural Selection In Important Class Of Genetic Elements." ScienceDaily. www.sciencedaily.com/releases/2008/12/081210121922.htm (accessed October 25, 2014).

Share This



More Fossils & Ruins News

Saturday, October 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Reuters - Innovations Video Online (Oct. 24, 2014) Miniature deep sea animals discovered off the Australian coast almost three decades ago are puzzling scientists, who say the organisms have proved impossible to categorise. Academics at the Natural History of Denmark have appealed to the world scientific community for help, saying that further information on Dendrogramma enigmatica and Dendrogramma discoides could answer key evolutionary questions. Jim Drury has more. Video provided by Reuters
Powered by NewsLook.com
Fossil Treasures at Risk in Morocco Desert Town

Fossil Treasures at Risk in Morocco Desert Town

AFP (Oct. 23, 2014) Hundreds of archeological jewels in and around the town of 30,000 people prompt geologists and archeologists to call the Erfoud area "the largest open air fossil museum in the world". Duration: 02:17 Video provided by AFP
Powered by NewsLook.com
Oldest Bone Ever Sequenced Shows Human/Neanderthal Mating

Oldest Bone Ever Sequenced Shows Human/Neanderthal Mating

Newsy (Oct. 23, 2014) A 45,000-year-old thighbone is showing when humans and neanderthals may have first interbred and revealing details about our origins. Video provided by Newsy
Powered by NewsLook.com
Weird-Looking Dinosaur Solves 50-Year-Old Mystery

Weird-Looking Dinosaur Solves 50-Year-Old Mystery

Newsy (Oct. 23, 2014) You've probably seen some weird-looking dinosaurs, but have you ever seen one this weird? It's worth a look. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins