ROUTES TO REPRESSION: The oldest LINE-1 transposons in the human genome are no longer transcribed due to the accumulation of mutations (1). DNA-binding proteins called KRAB-ZFPs and their partner KAP1 repress slightly younger LINE-1s, which originated in our ancestors’ genomes between 26.8 and 7.6 million years ago (2). KRAB-ZFPs have not evolved the ability to recognize more newly evolved transposons, which instead are repressed by methylation, possibly triggered by small RNAs called piRNAs (3).THE SCIENTIST STAFF
The paper
N. Castro-Diaz et al., “Evolutionally dynamic L1 regulation in embryonic stem cells,” Genes Dev, 28:1397-409, 2014.
Transposable elements—chunks of DNA that copy and reinsert themselves throughout chromosomes—make up about half of the human genome. Long interspersed element-1s (LINE-1s) are among the few transposable elements that are active in humans, continuing to express and amplify their 6–7 kilobases of DNA. They are a key driver of evolution, accounting for 20 percent of the genome, but their out-of-control proliferation can also harm cells.
In germ and embryonic cells, the control of LINE-1 activity is especially important, as any changes to the genome will be magnified as the organism develops. In adult cells such control is usually exerted through DNA methylation, but embryonic cells undergo an ...
