CAMBRIDGE, Mass. (August 7, 2011) The human genome is peppered with repeated DNA elements that can vary from a few to thousands of consecutive copies of the same sequence. During meiosisthe cell division that produces sperm and eggsrepetitive elements place the genome at risk for dangerous rearrangements from genome reshuffling. This recombination typically does not occur in repetitive DNA, in part because much of it is assembled into specialized heterochromatin. Other mechanisms that restrain recombination in repetitive DNA have remained elusive, until now.
In a paper published online today in the journal Nature, researchers in the lab of Whitehead Institute Fellow Andreas Hochwagen describe a defense mechanism in yeast that shields repetitive DNA from meiotic DNA recombination. According to the work of Hochwagen and his colleagues, the protective repeat-associated heterochromatin makes the DNA segments near the boundary of the heterochromatin particularly vulnerable to inappropriate meiotic recombination. DNA elements surrounding these at-risk border regions are protected from meiotic recombination by a novel system involving the concerted action of two proteins, pachytene checkpoint protein 2 (Pch2) and origin recognition complex subunit 1 (Orc1), which are present in organisms ranging from yeast to humans.
During meiosis an organism's chromosomes pair up, with every pair containing a copy inherited from each of the organism's parents. To match up the chromosomes, the cell breaks both strands of the chromosomes' DNA in multiple locations, and the chromosomes swap DNA sections that have the same sequence. Later, when the paired chromosomes are pulled apart, each resulting chromosome is a patchwork of maternal and paternal genes. The creation of reshuffled chromosomes assists chromosome assortment into spore, sperm, and egg cells, but it also has a profound effect on evolution, because it produces new genetic variants.
|Contact: Nicole Giese|
Whitehead Institute for Biomedical Research