Epigenetics Reveals Unexpected, and Some Identical, Results

We were always a bit skeptical of this island thing," he says. So the team used a method that could reveal every place in the genome where a methylation flag was staked.

The team did find characteristic patterns in each tissue type, but not in CpG islands, where researchers expected. Methylation flagged DNA in liver, spleen and brain at thousands of places along the CpG island shores. The shores contained about 76 percent of the methylation flags shown to be characteristic of specific tissue types.

This is a discovery that is totally unexpected," says Ohlsson. Feinberg's team has found "a signature of the genome that we weren't aware of before."

DNA in mouse tissues also has "shore" methylation patterns similar to those in corresponding human tissues. About 51 percent of the shores methylated in mouse tissues were also methylated in human tissues, indicating that DNA methylation of CpG island shores is an ancient, and important, method of controlling genes, Feinberg says.

When looking at colon tumors, the team found that methylation patterns in the shores of the cancer cells were more eroded than those in healthy colon cells. Feinberg says a breakdown in the patterns may cause colon stem cells to develop inappropriately, leading to cancer.

Unpublished research by Dag Undlien of the University of Oslo, done on sabbatical in Feinberg's lab, indicates that monozygotic twins share more shore methylation patterns than fraternal twins do, and are even more similar than Petronis'research suggests, Feinberg says.

Feinberg thinks evidence from his lab, though preliminary, indicates that DNA sequence does help determine epigenetic patterns. He calls Petronis' report, "a terribly interesting paper," but adds, "I think there may be a stronger genetic contribution than is suggested by his data."