Evolutionary Arms Race Within The Human Genome

September 29, 2014

Brett Smith for redOrbit.com Your Universe Online

New research from the University of California, Santa Cruz has revealed that two sets of primate genes have been battling it out over the millennia and this conflict has driven the complexity of primate genomes.

Published on Sunday in the journal Nature, the study found that genome jumping retrotransposons are constantly developing new ways to escape repression by another set of genes called repressors.

We have basically the same 20,000 protein-coding genes as a frog, yet our genome is much more complicated, with more layers of gene regulation. This study helps explain how that came about, said study author Sofie Salama, a research associate at the UC Santa Cruz Genomics Institute who led the study.

Retrotransposons are segments of genetic code that can copy themselves and then insert that copy back into the genome. These events can interrupt genes and trigger disease, based on where a new copy slips into the genome. Frequently the effect is negligible, and occasionally the effect is advantageous, potentially enhancing gene expression.

The high chance of negative outcomes means natural selection favors mechanisms that prevent jumping events in the form of repressor genes and proteins.

The repressors named in the new study are part of the biggest category of gene-regulating proteins in mammals, called KRAB zinc finger proteins. The human genome has more than 400 genes for these repressive DNA-binding proteins, and about 170 of them have developed since primates split from other mammals.

The way this type of repressor works, part of it binds to a specific DNA sequence and part of it binds other proteins to recruit a whole complex of proteins that creates a repressive landscape in the genome, Salama said. This affects other nearby genes, so now you have a potential new layer of regulation available for further evolution.

Previous research on KRAB zinc finger proteins found they repress jumping genes in mouse embryonic stem cells. In the new study, scientists placed primate retrotransposons in mouse embryonic stem cells that had a single human chromosome. The primate jumping genes suddenly sprang to life in the mouse cells. The study team developed a test to see which individual KRAB proteins could turn off a primate jumping gene in the mouse cell system.

Read the rest here:
Evolutionary Arms Race Within The Human Genome