|Researchers Test New Lab Method to Detect DNA
Damage Throughout the Genome
In laboratory experiments using budding yeast, the same type used
in baking and brewing, scientists at the National Cancer Institute
(NCI), part of the National Institutes of Health, developed a new
approach to determine the location of unrepaired breaks in DNA.
This new approach should better inform research as unrepaired DNA
damage often underlies the development of cancer. The research
findings appear in the December, 2007, issue of PloS Biology.
The investigators, from NCI's Center for Cancer Research (CCR),
examined meiosis, a form of cell division that produces sperm and
eggs in animals.
During meiosis, a process called recombination may occur that
involves the swapping of genetic material between chromosomes.
Chromosomes are molecules of DNA that carry genes and function
in the transmission of genetic information. For recombination to
occur, chromosomal DNA must first be broken and then spliced together
in new combinations, which creates genetic diversity as new combinations
of genes are passed from parent to child.
"Our new method to detect where DNA is purposefully broken
during meiosis should be a useful tool in understanding the events
that start cells on the road to cancer," said study author
Michael Lichten, Ph.D., of NCI's Laboratory of Biochemistry and
Recent research has shown that recombination is initiated during
meiosis when a protein called Spo11 breaks both strands of the
DNA molecule present in a chromosome. These double-strand breaks
(DSBs) are then efficiently repaired by recombination. While these
DSBs are useful during meiosis, DSBs formed by accident or by chemical
damage can be harmful because they are often incorrectly repaired,
creating the kind of genetic rearrangements that can cause cancer
and other diseases. By studying how yeast efficiently repair the
DSBs that occur during meiosis, researchers aim to develop ways
of reducing the impact of cancer-causing, unrepaired or improperly
repaired DNA damage.
When a DSB is caused by the Spo11 protein, the protein sometimes
remains attached to the end of the DSB. Previous methods of detecting
DSBs involved seeking the Spo11 protein to see what DNA was attached.
These methods are not sensitive, and do not detect all of the DSBs
that are formed during meiosis.
Instead of searching for the Spo11 protein, the researchers examined
the single strands of DNA that accumulate at DSBs in mutants that
lack critical recombination proteins. By purifying this single-stranded
DNA, they were able to map yeast DSBs during meiosis at the whole-genome
level. Because this approach finds breaks using a feature common
to all DSBs, it can be used in circumstances where Spo11 is not
involved, such as DSBs that are caused by chemical agents.
Using this new detection approach, the authors took a whole-genome
snapshot of DSB locations. While the previous, less sensitive studies
had suggested that DSBs did not occur in up to 40 percent of the
genome during meiosis, this more sensitive method showed that DSBs
were occurring at similar levels throughout the yeast genome.
The researchers concluded that recombination in yeast is distributed
much more uniformly than previously believed. They predict that
their new mapping method will be useful for studying recombination
and DNA damage in other organisms.
For more information on Lichten's laboratory, please go to http://ccr.cancer.gov/staff/staff.asp?profileid=5611.
For a basic tutorial on Cancer Genomics, please visit http://www.cancer.gov/cancertopics/understandingcancer/cancergenomics/.
For more information about cancer, please visit the NCI Web site
at http://www.cancer.gov, or
call NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237).
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