Featured Research

from universities, journals, and other organizations

Extra gene drove instant leap in human brain evolution

Date:
May 3, 2012
Source:
Cell Press
Summary:
A partial, duplicate copy of a gene appears to be responsible for the critical features of the human brain that distinguish us from our closest primate kin. The momentous gene duplication event occurred about two or three million years ago, at a critical transition in the evolution of the human lineage, according to a pair of new studies.

A partial, duplicate copy of a gene appears to be responsible for the critical features of the human brain that distinguish us from our closest primate kin. The momentous gene duplication event occurred about two or three million years ago, at a critical transition in the evolution of the human lineage, according to a pair of studies published early online in the journal Cell, a Cell Press publication, on May 3rd.

Related Articles


The studies are the first to explore the evolutionary history and function of any uniquely human gene duplicate. These "extra" genes are of special interest as they provide likely sources of raw material for adaptive evolutionary change. Until now, studying them has been a technical challenge because they are nearly indistinguishable from each other.

"There are approximately 30 genes that were selectively duplicated in humans," said Franck Polleux, an expert in brain development at The Scripps Research Institute. "These are some of our most recent genomic innovations."

Intriguingly, many of these genes appear to play some role in the developing brain. Polleux and Evan Eichler, a genome scientist at the University of Washington, focused their expertise and attention on one of the genes known as SRGAP2. This gene has, in fact, been duplicated at least twice during the course of human evolution, first about 3.5 million years ago and then again about 2.5 million years ago.

The new work shows that the second and relatively recent duplication event produced only a partial copy of the gene. This copy acts at exactly the same time and place as the original, allowing it to interact with and block the ancestral gene's function.

"This innovation couldn't have happened without that incomplete duplication," Eichler said. "Our data suggest a mechanism where incomplete duplication of this gene created a novel function 'at birth'."

Interestingly, the novel gene appears to have arisen just as the fossil record shows a transition from human's extinct Australopithecus ancestors to the genus Homo (as in Homo sapiens), which led to modern humans. That's also when the brains of our ancestors began to expand and when dramatic changes in cognitive abilities are likely to have emerged.

The researchers don't think SRGAP2 is solely responsible for that brain expansion, but the genetic interference does have potential benefits. Polleux and colleagues mimic the function of the human-specific SRGAP2 duplication in mice. They show that loss of SRGAP2 function accelerates neurons' migration in the developing brain, potentially helping them reach their final destination more efficiently. Moreover, neurons that have decreased SRGAP2 function, due to expression of the human-specific SRGAP2 display more knob-like extensions or spines on their surfaces, making the neurons appear much more like those found in the human brain. These spines enable connections between neurons to form.

In addition to providing insight into the origins of the modern human brain, the findings offer clues to the neurodevelopmental disorders that humans are so prone to developing, including autism, epilepsy and schizophrenia, in which development of neuronal connections is affected. The researchers point to known cases of humans with structural brain defects and other symptoms that can be traced to disruption of the ancestral SRGAP2. They now intend to search for people carrying defects in the human-specific 'granddaughter' copy as well.

If this gene duplication did indeed produce an immediate effect during evolution as Eichler and Polleux suspect, they expect there must have been a fascinating period in human history characterized by "huge variation" in human cognition and behavior. SRGAP2 and other human-specific gene duplicates might also help to explain the big differences between humans and other primates, despite few apparent differences in our genome sequences.

"We may have been looking at the wrong types of mutations to explain human and great ape differences," Eichler says. "These episodic and large duplication events could have allowed for radical -- potentially earth-shattering -- changes in brain development and brain function."


Story Source:

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


Journal References:

  1. Cécile Charrier, Kaumudi Joshi, Jaeda Coutinho-Budd, Ji-Eun Kim, Nelle Lambert, Jacqueline de Marchena, Wei-Lin Jin, Pierre Vanderhaeghen, Anirvan Ghosh, Takayuki Sassa, Franck Polleux. Inhibition of SRGAP2 Function by Its Human-Specific Paralogs Induces Neoteny during Spine Maturation. Cell, 2012; DOI: 10.1016/j.cell.2012.03.034
  2. Megan Y. Dennis, Xander Nuttle, Peter H. Sudmant, Francesca Antonacci, Tina A. Graves, Mikhail Nefedov, Jill A. Rosenfeld, Saba Sajjadian, Maika Malig, Holland Kotkiewicz, Cynthia J. Curry, Susan Shafer, Lisa G. Shaffer, Pieter J. de Jong, Richard K. Wilson, Evan E. Eichler. Evolution of Human-Specific Neural SRGAP2 Genes by Incomplete Segmental Duplication. Cell, 2012; DOI: 10.1016/j.cell.2012.03.033

Cite This Page:

Cell Press. "Extra gene drove instant leap in human brain evolution." ScienceDaily. ScienceDaily, 3 May 2012. <www.sciencedaily.com/releases/2012/05/120503125804.htm>.
Cell Press. (2012, May 3). Extra gene drove instant leap in human brain evolution. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2012/05/120503125804.htm
Cell Press. "Extra gene drove instant leap in human brain evolution." ScienceDaily. www.sciencedaily.com/releases/2012/05/120503125804.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:

More Coverage


Scientists Show How a Gene Duplication Helped Our Brains Become 'human'

May 3, 2012 — Scientists have shown that an extra copy of a brain-development gene, which appeared in our ancestors’ genomes about 2.4 million years ago, allowed maturing neurons to migrate farther and develop ... read more

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