The duplication of the SRGAP2 made us more human

For years, researchers have been looking for differences between the genome of humans and other primates to explain what distinguish us from our closest primate kin. Until the moment, the main way to make those comparisons consisted onsearching changes of the sequence of nucleotides.

However, studies published in Cell, suggest DNA duplication errors that occurred millions of years ago might be important in the evolution of the complexity of the human brain. These duplications may have allowed our brain to make more neural connections at greater distances, shaping our brains into what they are now.

In 2010, a group led by Evan Eichler,identified 23 genes that have only been duplicated in humans, and no other apes. Among these, SRGAP2 stood out.

Years later, two groups led by Evan Eichler and Franck Polleux found that humanshave three copies of the SRGAP2 gene. The second of these copies, SRGAP2C, is particularly interesting because it affects the development of neurons, and produces characteristicsthat are distinctively human.

The authors found that the original gene was first duplicated around 3.4 million years ago to create SRGAP2B. This copy was itself duplicated 2.4 million years ago to create SRGAP2C, and again 1 million years ago to produce SRGAP2D. These copies have evolved in different ways. Whilst B and D versions have probably mutated to the point that they are genetic junk, the C-copy is very different.

The SRGAP2C protein blocks the action of the protein coded by the ancestral gene. According to the team, the inhibition if the SRGAP2A (ancestral) protein, allows neurons to acquire a new function: neurons would produce denser called dendritic spines.

“If you’re increasing the total number of connections, you’re probably increasing the ability of this network to handle information,” Polleux says. "It’s like increasing the number of processors in a computer."

There is still a lot to discover, SRGAP2 is just one of more than 30 genes that have been duplicated specifically in humans. The teams are now busy trying to analyze these genes and understand their evolution.

James Sikela, and evolutionary geneticist at the University of Colorado, and his team have identified some duplicated genes that are unique in humans. “Finding the genes that make us human may be challenging,” he says, “but the resources we now have to ask such questions are unprecedented.”

Divulgation article: http://www.nature.com/news/human-brain-shaped-by-duplicate-genes-1.10584?WT.ec_id=NEWS-20120508

Original article: https://www.sciencedaily.com/releases/2012/05/120503125804.htmhttps://www.sciencedaily.com/releases/2012/05/120503125804.htm

#SRGAP2C #Neurons #Gene #Genomic #Protein #Duplication #Human #DNA #Research