A chemical tweak to the genome

For the past 40 years, biologists have been searching for something they weren’t sure even existed—a chemical modification of DNA (or, a new base) that changes the functions of the mammalian genome. Although such bases exist in bacteria, until several months ago it was widely accepted that they do not exist in mammals, with one exception. Andrew Xiao, Ph.D., associate professor of genetics, and his lab have discovered a second elusive base hidden within an ancient virus that inserted itself into the genome 1.5 million years ago, according to a study funded by an anonymous donor and published in Nature. This mechanism can turn off neighboring genes along the genome, and it’s also responsible for determining the sex ratio in mammalian populations. (When the gene underlying this mechanism is deleted, twice as many males are born as females.) But Xiao sees another use for this modification. “Because it’s so rare, it must be upregulated in certain disease conditions,” he said. In other words, in certain disease states, this modification may kick into action as emergency relief.