Another genetic difference between humans & chimps

adult-chimp-at-bwindi-national-park.JPGResearchers have identified another difference between our genome and that of our closest living relative, the chimpanzee Pan troglodytes.

Here’s the abstract from the Science paper, by Popesco et al:

Extreme gene duplication is a major source of evolutionary novelty. A genome-wide survey of gene copy number variation among human and great ape lineages revealed that the most striking human lineage specific amplification was due to an unknown gene, MGC8902, which is predicted to encode multiple copies of a protein domain of unknown function (DUF1220). Sequences encoding these domains are virtually all primate-specific, show signs of positive selection, and are increasingly amplified generally as a function of a species’ evolutionary proximity to humans, where the greatest number of copies (212) is found. DUF1220 domains are highly expressed in brain regions associated with higher cognitive function, and in brain show neuron-specific expression preferentially in cell bodies and dendrites.

A comparison of the genomes of humans, chimps and macaques revealed that humans have 49 copies of the MGC8902 gene, whereas chimps have 10, and macaques just 4. And it is not just the gene that has been amplified; a region within it has undergone further amplification in the human lineage.

The region encodes a domain called DUF1220, which is repeated 212 times in humans but only 37 times and 30 times in chimps and macaque monkeys, respectively. Amplification of the DUF1220 domain appears to be specific to the primate lineage, as mice and rats have only one copy in their MGC8902 gene. There are other human genes containing the DUF1220 domain, and it has been amplified in those genes as well.

DUF1220 is one of several thousand sequences in the human genome encoding protein domains of unknown function. I don’t know what DUF stands for, but I’ll hazard a guess that it’s an abbreviation for Domain of Unknown Function. The authors speculate that amplification of the domain in humans is somehow related to brain evolution:

In light of the strong DUF1220 expression we observed in neurons of the neocortex, it is intriguing that multiple independent evolutionary processes [brain enlargement, neocortex expansion, gene duplication, and domain amplification] can be seen as having individually and cumulatively contributed to increasing the DUF1220-coding potential of the human brain, suggesting that such an increase may have conferred strong selective advantages.

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