The cell-cycle field has identified the core regulators that drive the cell cycle, but we do not have a clear map of the dynamics of these regulators during cell-cycle progression versus cell-cycle exit. Here we use single-cell time-lapse microscopy of Cyclin-Dependent Kinase 2 (CDK2) activity followed by endpoint immunofluorescence and computational cell synchronization to determine the temporal dynamics of key cell-cycle proteins in asynchronously cycling human cells. We identify several unexpected patterns for core cell-cycle proteins in actively proliferating (CDK2-increasing) versus spontaneously quiescent (CDK2-low) cells, including Cyclin D1, the levels of which we find to be higher in spontaneously quiescent versus proliferating cells. We also identify proteins with concentrations that steadily increase or decrease the longer cells are in quiescence, suggesting the existence of a continuum of quiescence depths. Our single-cell measurements thus provide a rich resource for the field by characterizing protein dynamics during proliferation versus quiescence.

细胞周期领域已经确定了驱动细胞周期的核心调节因子，但我们没有关于这些调节因子在细胞周期进展与细胞周期退出期间的动态的清晰图谱。在这里，我们使用单细胞延时显微镜观察细胞周期蛋白依赖性激酶 2 (CDK2) 活性，然后使用终点免疫荧光和计算细胞同步来确定异步循环人类细胞中关键细胞周期蛋白的时间动态。我们发现了活跃增殖（CDK2 增加）与自发静止（CDK2 低）细胞中核心细胞周期蛋白的几种意想不到的模式，包括 Cyclin D1，我们发现其水平在自发静止细胞与增殖细胞中更高。我们还发现，随着细胞静止时间的延长，蛋白质的浓度会稳定地增加或减少，这表明存在连续的静止深度。因此，我们的单细胞测量通过表征增殖与静止期间的蛋白质动态特征，为该领域提供了丰富的资源。