It’s all in the packaging. How nature wraps and tags genes determines if and when they become active, according to researchers from Harvard and M.I.T. They did the largest, most detailed study to date of the protein structure that surrounds the human genome. Their findings reveal surprising and previously unknown specifics of how genes get switched on during development of the human body and in diseases such as cancer. “Each type of cell in our bodies contains the same genes. What makes them do different things involves which genes are turned on,” notes Bradley Bernstein, a pathologist at Harvard Medical School. The analysis shows a striking and surprising exception in the way some critical genes are activated by the protein packaging. The big surprise involves clusters of so-called “HOX” genes, which apparently work in concert to control how we develop in the womb. Instead of being activated individually like most genes, the HOX genes appear to be turned on in groups by massive numbers of tags. HOX genes also are deeply involved in cancer, making the findings particularly important. Some of the proteins that regulate HOX genes are capable of causing or suppressing tumors. “Many of the proteins that regulate these genes can suppress or enhance tumor growth,” Bernstein notes. “Some of the genes can cause cancer directly when altered by mutations.” “The work we’re doing now is very fundamental,” he says. “But what we learn about the interactions between chromatin, its tags, and various proteins that interact with them may one day be useful for understanding, diagnosing, and even developing new treatments for some cancers.”