Featured Research

from universities, journals, and other organizations

Life On Land Tied To Gene Expansion

Date:
February 4, 2000
Source:
Harvard Medical School
Summary:
The evolutionary transition from life in the sea to life on land may have been nudged by a genetic expansion, according to an article appearing in the February Development. HMS researchers Susan Dymecki and her colleagues suggest that a gene previously expressed in the developing brain may have come to be expressed also in the tips of developing limbs, helping to bring about the development of toes and fingers in the first vertebrates.

Boston, MA -- February 3, 2000 -- The evolutionary transition from life in the sea to life on land may have been nudged by a genetic expansion, according to an article appearing in the February Development. HMS researchers Susan Dymecki and her colleagues suggest that a gene previously expressed in the developing brain may have come to be expressed also in the tips of developing limbs, helping to bring about the development of toes and fingers in the first vertebrates.

"So you get expansion of gene expression--not expression of a new gene--just expansion to a new area," says Dymecki, HMS assistant professor of genetics. She and colleagues Scott Baur and Jia J. Mai have recently identified the structure of the gene and also the genetic switch that may have brought about this expansion.

Until recently, the gene, which codes for a receptor found in the brains and skeletons of all vertebrates living today, was thought to be controlled by a single switch, or promoter. If that were true, a defect in the promoter should affect expression in the brain as well as the skeleton. But the researchers found that while mutant mice carrying such a defect almost totally lacked fingers and toes, their brains appeared, for the most part, normal. On closer inspection, the researchers found that there was not one but two promoters, one controlling gene expression in the brain, the other, which carried the mutation, in the limbs. The defective promoter was farthest away from the gene. "This is the first time anyone has seen this distal promoter," says Dymecki.

She and Baur, who is a graduate student, believe that this more distant promoter evolved more recently, perhaps as a result of a duplication of the one lying closer to the gene. Once formed, the new promoter may have accumulated mutations that enabled it to interact with transcription factors found in developing limb cells. As a consequence, the receptor previously expressed in the brain would have come to be expressed in the limb buds. Baur is currently comparing the two promoters to see if he can find signs of a duplication.

Meanwhile, the findings suggest that the origin of life on land may have entailed not just the invention of new genes but also putting old ones to new uses. It is a process nature has used many times before, Dymecki says. The Hox genes, which were first found to regulate body shape in flies and are now known to regulate body and limb development in vertebrates, produce their wide variety of effects by being expressed in different amounts at different times and places. It is not clear how the newly discovered promoter may have brought about the wide variety of vertebrate digits‹from the frog¹s grasping toes to the stubby toes of a human. Dymecki and her colleagues have been developing a system for identifying how variations between species have evolved.

"These are things we¹re still fleshing out," Dymecki says. "I would have to say it¹s been a real whirlwind just to get this paper out." In fact, their current paper appears back-to-back in Development with a paper by a group at UCLA. The California researchers knocked-out the receptor gene in the brain and digits of mice. Intriguingly, the knockout mice exhibited the same phenotype as the HMS mutants. They lacked digits but their brains were apparently normal. One explanation for why effects in the brain were masked is that the receptor may play such an important role there that nature has provided a genetic backup to make sure that its job gets done.

If it weren¹t for a twist of nature, Dymecki and he colleagues would never have identified the second promoter. Dymecki¹s whole excursion into skeletal development "was definitely serendipity," she says. In the course of studying brain development--her primary interest--Dymecki had generated a series of transgenic mice, each with a piece of DNA wedged into a different part of the genome (see sidebar). When she and her colleagues tried ear tagging one, they discovered that the mouse was unable to grab the table top.

It turned out, the mice had failed to develop digits. Suspecting that the piece of DNA had wedged itself into the middle of a gene for skeletal development, the researchers homed in on the gene, which produced IB bone morphogenetic protein receptor (BMPRIB). The protein was known to play a role in skeletal development, specifically the laying down of the cartilaginous blueprint that eventually develops into the bony skeleton. But no one had actually mapped out the structure of the gene (BmprIB)--that is, how exactly it was broken up into functional units, or exons.

After identifying the structure of BmprIB, Baur was able to determine that the chunk of DNA had integrated and essentially knocked out what appeared to be the promoter. The lack of any apparent defect in the brain of their mutant--at the time they did not know that even knockouts show no brain defects--led them to look for a second regulatory element.

Dymecki and her colleagues plan to use the transgenic system to see how, exactly, the limb-region promoter turns on BmprIB during mouse development‹in what cells and at what times. Comparing BmprIB regulation in mice to other animals could provide a first step to understanding how the extraordinary array of land-dwelling adaptations have evolved in different species. "We want to understand what regulatory elements are involved and what the evolutionary implications of those elements are in terms of species-to-species variation in digit formation," says Dymecki. "It does make me chuckle that it all came out of a simple transgenic insertion."


Story Source:

The above story is based on materials provided by Harvard Medical School. Note: Materials may be edited for content and length.


Cite This Page:

Harvard Medical School. "Life On Land Tied To Gene Expansion." ScienceDaily. ScienceDaily, 4 February 2000. <www.sciencedaily.com/releases/2000/02/000204074047.htm>.
Harvard Medical School. (2000, February 4). Life On Land Tied To Gene Expansion. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2000/02/000204074047.htm
Harvard Medical School. "Life On Land Tied To Gene Expansion." ScienceDaily. www.sciencedaily.com/releases/2000/02/000204074047.htm (accessed October 22, 2014).

Share This



More Plants & Animals News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Cadaver Dogs Aid Search for More Victims of Suspected Indiana Serial Killer

Cadaver Dogs Aid Search for More Victims of Suspected Indiana Serial Killer

Reuters - US Online Video (Oct. 21, 2014) — Police in Gary, Indiana are using cadaver dogs to search for more victims after a suspected serial killer confessed to killing at least seven women. Linda So reports. Video provided by Reuters
Powered by NewsLook.com
White Lion Cubs Unveiled to the Public

White Lion Cubs Unveiled to the Public

Reuters - Light News Video Online (Oct. 21, 2014) — Visitors to Belgrade zoo meet a pair of three-week-old lion cubs for the first time. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
'Cadaver Dog' Sniffs out Human Remains

'Cadaver Dog' Sniffs out Human Remains

AP (Oct. 21, 2014) — Where's a body buried? Buster's nose can often tell you. He's a cadaver dog, specially trained to find human remains and increasingly being used by law enforcement and accepted in courts. These dogs are helping solve even decades-old mysteries. (Oct. 21) Video provided by AP
Powered by NewsLook.com
White Lion Cubs Born in Belgrade Zoo

White Lion Cubs Born in Belgrade Zoo

AFP (Oct. 20, 2014) — Two white lion cubs, an extremely rare subspecies of the African lion, were recently born at Belgrade Zoo. They are being bottle fed by zoo keepers after they were rejected by their mother after birth. Duration: 00:42 Video provided by AFP
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