People turn gray, Harvard scientists found, when certain adult stem cells gradually die off. The stem cells provide a continuous supply of other, pigment-producing cells that give your hair its natural color. These same types of pigment cells, called melanocytes, can become cancerous in melanoma, the lethal form of skin cancer that killed about 8,000 people in the United States alone during the past year. “Preventing the graying of hair is not our goal,” says David E. Fisher, a Harvard Medical School scientist who directs the Program in Melanoma at Dana-Farber Cancer Institute in Boston. “Our goal is to prevent or treat melanoma. We would love to identify a signal that would make melanoma cells stop growing.” Fisher and his team have done this, at least in a laboratory dish, they reported in the December 2004 issue of the science journal Cancer Cell. Working together for the past two years, the team uncovered a protein called CDK2, which the cancer cells cannot live without. Find a way to block the activity of CDK2 and melanoma cells should stop growing. That’s the hope.