Scientists have discovered that the sun’s damaging ultraviolet (UV) rays target a series of biochemical signals inside the young skin cell, impairing the cell’s ability to control its proliferation. Lynda Chin and her colleagues found that they could increase both the number of tumors and the speed with which they formed by exposing newborn mice with an intact Rb pathway to UV radiation. (A pathway is a chain of biochemical signals that regulates cellular activity.) Those mice in which the Rb pathway was already essentially knocked out were unaffected by the dose of UV radiation. “It looks like the Rb pathway is specifically targeted by ultraviolet radiation,” said Chin, the study’s senior author. Chin is a researcher at Dana-Farber Cancer Institute in Boston and an assistant professor of dermatology at Harvard Medical School. She and her colleagues published their findings in the Feb. 4, 2003 Proceedings of the National Academy of Sciences.