Aug 31, 2006    #135
Contact: Wandra Green
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Gene duplication, not just divergence, helps make Humans unique

Researchers from the University of Missouri-Kansas City (UMKC) and the University of Colorado Health Sciences Center (UCHSC) have identified a whole class of small, repeated elements found in genes expressed in the brain that may help make humans distinct from other primates. In the search to identify uniquely human genetic traits, many particular genes emerged as interesting study targets for their roles in reproduction and brain development.

In the Sept. 1, 2006, issue of the journal Science, Popesco et al. report that one class of repetitive elements present in a number of genes are over-represented in great apes, and particularly Humans. Additionally, some subsets of these elements show all the earmarks of so-called “Darwinian” or adaptive selection, indicating that the segments may have been beneficial to the organisms over time.

The segments, called DUF1220 repeats, were found consistently in neurons, and in many regions of the brain particularly the neo-cortex, the region associated with higher thought in humans. While the researchers do not yet understand the function of these repeats, their rapid evolution and high amplification in humans underscores the need for further functional study of these regions to determine if they play a role in cognition.

The segments were identified following work in the lab of Dr. James M. Sikela at UCHSC looking at segments of DNA over-represented in humans compared to other primates. His group then looked at the patterns of expression of these repeats and determined where within the genome the repeats were found.

“You have a case here where the repeats are, in many instances, evolving very rapidly as they are being duplicated within the great ape lineage, notably within humans,” said Gerald Wyckoff, Ph.D., Assistant Professor, UMKC’s School of Biological Sciences and an author on this study. “This certainly suggests that these domains are playing some important role within cells. The pattern we are seeing does not fit what you would expect from a random, or so-called “neutral” evolutionary model,” he said. Wyckoff examined the patterns of molecular evolution and saw that in many cases the repeats appeared to be under adaptive selection.

The subject of future research will be to precisely determine the role of the repeated genetic segments. However, the study raises the prospect that adaptation may be occurring even over relatively short periods of evolutionary time by mechanisms more dramatic then the replacement of single nucleotides and amino acids within functional genes.

The University of Missouri-Kansas City (UMKC), one of four University of Missouri campuses, is a public university serving more than 14,000 undergraduate, graduate and professional students. UMKC engages with the community and economy based on a three-part mission: visual and performing arts, health sciences, and urban affairs.

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