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Synopses of Research Articles Quiet Time: Gene Program Prevents Division but Keeps Cells at the Ready Richard Robinson | DOI: 10.1371/journal.pbio.0040085 Because uncontrolled cell division is so dangerous for an which regulate multiple other genes. Over time, however, the organism, the well-behaved cell must know not only when number of overlapping genes increased. After 20 days, there to divide, but also—crucially—when not to. Shutting down were over 100 genes whose change in expression linked them cell division prevents tumors and maintains the proper form to quiescence. These included not only those that regulate of tissues such as muscle. Many cells, though, including metabolism and cell division, as might be expected, but also fi broblasts, must also retain the ability to start dividing genes that suppress the transition to two other cell fates— again when conditions are right—when the organism must differentiation and programmed death. The expression grow, or a damaged tissue must be repaired. A cell in such a of these genes (along with many others) was increased, temporary, nondividing state is said to be “quiescent.” Signals indicating the active nature of the quiescent state. that send a cell into quiescence include loss of contact with The reversibility of quiescence contrasts with the cell cycle the underlying surface, too much contact with neighboring arrest induced by inhibition of cyclin-dependent kinase cells, and not receiving specifi c growth factors from the (CDK), a key regulatory protein. When the authors treated surroundings. fi broblasts with a CDK inhibitor, division stopped, but the Despite its importance, little is known about