Solving DNA Organization Puzzle.

• Position: HUMAN CHROMATIN

Stretched out, the DNA from all the cells in our body would reach Pluto. So, how does each tiny cell pack a two-meter length of DNA into its nucleus, which is just one-thousandth of a millimeter across? The answer to this daunting biological riddle is central to understanding how the three-dimensional organization of DNA in the nucleus influences our biology, from how our genome orchestrates our cellular activity to how genes are passed from parents to children.

Scientists at the Salk Institute, La Jolla, Calif., and the University of California, San Diego, have provided an unprecedented view of the 3D structure of human chromatin--the combination of DNA and proteins--in the nucleus of living human cells.

In the study, researchers identified a novel DNA dye that, when paired with advanced microscopy in a combined technology called ChromEMT, allows highly detailed visualization of chromatin structure in cells in the resting and mitotic (dividing) stages. By revealing nuclear chromatin structure in living cells, the work may help rewrite the textbook model of DNA organization and even change how we approach treatments for disease.

"One of the most-intractable challenges in biology is to discover the higher-order structure of DNA in the nucleus and how this is linked to its functions in the genome," says senior author Clodagh O'Shea of the Molecular and Cell Biology Laboratory at Salk and faculty scholar at Howard Hughes Medical Institute. "It is of eminent importance, for this is the biologically relevant structure of DNA that determines both gene function and activity."

Ever since Francis Crick and James Watson determined the primary structure of DNA to be a double helix, scientists have wondered how DNA is further organized to allow its entire length to pack into the...