Key Protein May Hold Clue to Brain Development
Humans and apes have been found to have around 100 times more of a newly discovered protein when compared with a mouse, say U.S. researchers, leading them to believe they have discovered the key to cognition.
Published in the print edition of Science, the authors examined the genomes of humans and great apes searching for genes which had increased in number to an unusual extent.
"It is known that gene duplication is a major driving force of evolutionary change, so we felt the chance to survey virtually all human genes at once and ask which had duplicated in a human-lineage specific manner, was a great opportunity to find genes important to human-specific traits," said James Sikela of the University of Colorado in Denver, co-author of the study.
They found that a gene with the unwieldy name of MGC8902 had increased significantly in humans and the apes that are evolutionarily thought to be closer to humans were also found to have more copies of this gene.
The authors said that MGC8902 codes for multiple copies of a protein component with the equally unmemorable name of DUF1220. While its function remains unknown, Sikela is willing to make a prediction: "We have reason to suspect it might be important to brain evolution and possibly human cognition," he said.
The significant increase in DUF1220 sequences in primates and especially in humans illustrates how dynamic the genome can be in certain regions. “It is an example of how quickly evolutionary change can occur, even in humans and great apes,” said Sikela.
The authors said that the higher level of DUF1220 in human and African great apes suggests that they are important to evolutionary traits that are found more prominently in these species.
"We believe that non-mammals have no DUF1220 [gene]... while non-primate mammals - mice, dogs, whales, etc - have only one. In contrast, humans have well over 100, though the exact number is not yet known," said Sikela.
However, the authors do know that DUF1220 protein components are seen in some neurons, and are especially abundant in the neocortex - part of the brain involved in higher reasoning including language and conscious thought in humans. According to the authors, the number of copies of the DUF1220 gene in a species seems to run in parallel with the evolution of the neocortex.
Sikela notes that there is much more to learn about DUF1220 protein components and their function, and whether they are associated with any particular types of disease. He thinks that other important evolutionary genes also require thorough investigation.
"We think that the method we used to discover DUF1220 domain amplification in humans is a very powerful tool to look for other genes that are important to human and primate evolution," said Sikela. "We hope to use it to look for other evolutionarily important genes."