The new 3-D microscope developed by University of California biophysicists has shown researchers that the nucleus, which contains the lion's share of the genome, “is much more highly organized than everybody thought,” says John Sedat, a professor of biochemistry and biophysics at the University of California , San Francisco . “This is an example of what this technology can deliver on.”

In this image of a nucleus from a mouse-muscle stem cell, three elements are visible. The membrane surrounding the nucleus is stained blue. The nuclear pores, proteins through which RNA, water, and other molecules pass, are stained green. Inside the nucleus, DNA, which has doubled and condensed in preparation for cell division, is stained red.