Science ( IF 41.845 ) Pub Date : 2020-07-31 , DOI: 10.1126/science.369.6503.495 Elizabeth Pennisi
Textbooks speak of four DNA building blocks, whose order specifies genes. But researchers have also identified four chemically modified versions of these nucleoside bases, which affect how genes are expressed. One, methylated adenine, is mired in controversy about whether it exists in mammals. Now, researchers have not only identified plenty of this modified base in mouse embryonic cells, but they also found that it plays a key role in the development of the placenta. It stalls differentiation of cells destined to become the placenta by pausing gene activity. The methylated base—methyladenine for short—gives cells another epigenetic tool for turning genes on or off during normal development or in disease.