A simple reentry into the cell cycle

It may be specialized, but a muscle cell is just a single step away from resuming division, as Pajalunga et al. reveal on page 807. The researchers show that removing one regulatory protein can push a range of nondividing cells back into the cell cycle.

Most cells in adults aren't cycling. Some have slipped into quiescence, a temporary lull triggered by scarcity of food or other necessities. Cells whose telomeres have worn down or that carry damaged DNA often retire by entering replicative senescence. And terminally differentiated cells are so specialized that they no longer divide. Although researchers can jump-start the cell cycle by, for example, adding growth factors, the recipe for reactivating cells in each state is different.

To their surprise, Pajalunga et al. found that a common factor, a protein called p21,...