Author Topic: Fastest-evolving human gene linked to brain boost  (Read 403 times)

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Fastest-evolving human gene linked to brain boost
« on: August 26, 2006, 07:30:46 AM »
Fastest-evolving human gene linked to brain boost

http://www.newscientist.com/article/dn9767-fastestevolving-human-gene-linked-to-brain-boost.html

The fastest evolving gene in the human genome is one linked to brain development, researchers say.

A study of differences between the human and chimp genomes has identified a gene associated with neural growth in the cerebral cortex – the part of the brain involved in processing thoughts and learning – as having undergone “accelerated evolutionary change”.

Katherine Pollard and colleagues at the University of California Santa Cruz, US, suggest that the fast-changing gene may help explain the dramatic expansion of this part of the brain during the evolution of humans.

They identified the rapidly evolving region of DNA – called human accelerated region 1 (HAR1) – after carrying out an extensive computational comparison between the genomes of humans, chimpanzees and other vertebrates.
Critical role

There are only two changes in the 118 letters of DNA code that make up HAR1 between the genomes of chimps and chickens. But chimps and humans are 18 letter-changes apart. And those mutations occurred in just five million years, as we evolved from our shared ancestor.

“That is an incredible amount of change to have happened in a few million years,” Pollard notes.

Subsequent experiments looking at the brains of human and primate embryos revealed that HAR1 is part of two overlapping genes. One of these genes, called HAR1F is active in nerve cells that appear early in embryonic development and play a critical role in the formation of the layered structure of the human cerebral cortex.

The role of the other gene, called HAR1R, is less clear, but it also appears also to be involved in cortex development.
"Very suggestive"

The researchers point out that these genes do not appear to code for any proteins, but are what is known as an RNA genes.

“We don’t know exactly what it does, but the evidence is very suggestive that HAR1F is important in the development of the cerebral cortex, and that’s exciting because the human cortex is three times as large as it was in our predecessors,” says David Haussler, director of the Center for Biomolecular Science and Engineering at the University of California Santa Cruz, who assisted with the study.

“Something caused our brains to evolve to be much larger and have more functions than the brains of other mammals,” he points out.

Journal reference: Nature (DOI: 10.1038/nature05113)

Abstract to the paper:

Quote
An RNA gene expressed during cortical development evolved rapidly in humans

Katherine S. Pollard1,7,8, Sofie R. Salama1,2,8, Nelle Lambert4,5, Marie-Alexandra Lambot4, Sandra Coppens4, Jakob S. Pedersen1, Sol Katzman1, Bryan King1,2, Courtney Onodera1, Adam Siepel1,7, Andrew D. Kern1, Colette Dehay6, Haller Igel3, Manuel Ares, Jr3, Pierre Vanderhaeghen4 and David Haussler1,2
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Abstract

The developmental and evolutionary mechanisms behind the emergence of human-specific brain features remain largely unknown. However, the recent ability to compare our genome to that of our closest relative, the chimpanzee, provides new avenues to link genetic and phenotypic changes in the evolution of the human brain. We devised a ranking of regions in the human genome that show significant evolutionary acceleration. Here we report that the most dramatic of these 'human accelerated regions', HAR1, is part of a novel RNA gene (HAR1F) that is expressed specifically in Cajal–Retzius neurons in the developing human neocortex from 7 to 19 gestational weeks, a crucial period for cortical neuron specification and migration. HAR1F is co-expressed with reelin, a product of Cajal–Retzius neurons that is of fundamental importance in specifying the six-layer structure of the human cortex. HAR1 and the other human accelerated regions provide new candidates in the search for uniquely human biology.
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