The Per2 gene helps measure the pace of the circadian rhythm—and now it appears that it also helps keep cancer at bay, according to a study in the October 4 Cell. Fu et al. suspected a connection to cancer when they found hyperplasia in the salivary glands of relatively young Per2-mutant mice. They next tested the animals' sensitivity to radiation, an indication of cancer susceptibility. Irradiation can damage the cells responsible for hair color. Indeed, after irradiation all of the Per2 mutant mice developed prematurely gray hair (shown here) And a high frequency of lymphomas as compared to wild-type mice. Mutant mice also had aberrant temporal expression of genes involved in cell cycle regulation and tumor suppression. The researchers honed in on a mechanism for circadian control of one such gene, the p53 regulator c-myc. Its transcription is controlled directly by two PER2-controlled clock proteins. The results jibe with previous findings hinting at a link between circadian cycles and cancer; for example, women working the night shift appear to have an increased risk of breast cancer.

Credit: Reprinted with permission from Elsevier Science