While it was Caligiuri's laboratory that designed the mouse model, it was Plass who supervised the methylation studies. He and his colleagues used a system called Restriction Landmark Genome Sequencing (RLGS) to compare methylation patterns among the three groups of mice a method of using enzymes and gel electrophoresis to map tiny bits of DNA on a grid. The stretches of DNA, referred to as fragments, show up as smudgy blobs on a test film. If a fragment is dark and definite, it is not methylated. If, on the other hand, it loses at least 30 percent of its intensity, it is regarded as methylated.
In the study, the research team tested 2447 fragments in each animal. They found anywhere from 45 to 209 (.8 percent to 8.5 percent) of the fragments methylated in the mice with cancer, but only one or two methylated fragments in the other mice.
"Interestingly, that same range of methylated fragments is exactly what we find in human leukemia, too," says Caligiuri, "so that gives added merit to our mouse model as an investigative tool."
Using data from the methylation studies, Caligiuri and Plass were able to identify a particular stretch of DNA, called Id4, as a tumor suppressor gene.
Tumor suppressor genes help control cancer by identifying and getting rid of defective cells before they have a chance to mature and divide. When tumor suppressor genes lose that ability as they can if they are silenced through methylation or some other process, it gives cancer a chance to establish a foothold and spread.
Caligiuri says much more work needs to be done, but adds that the identification of Id4 as a likely tumor suppressor gene gives clinicians another possible target for intervention.
"We already have a drug, decitabine, that we know can reverse the effects of methylation," says Plass. "We are just beginning to figure out how it best works in humans, but simply knowing that we have a new target that may be meanin
Contact: Michelle Gailiun
Ohio State University