Cell cycle exit in G1. (A) Cells were plated on large, fibronectin-coated discoidal micropatterns to prevent them from escaping the observation field. They were monitored by time-lapse microscopy to measure cell division time with respect to the time of starvation and to follow the fate of daughter cells. The red cell illustrates starvation in early G1: the cell divided 2.5 h before starvation and stopped dividing after. The blue cell illustrates starvation in late G1: the cell divided 5 h before starvation and divided again after. See corresponding Video 1 and Fig. S1. Bar, 100 µm. (B) The histogram shows the proportion of dividing and nondividing cells, depending on the cell cycle stage when starvation occurred (S, n = 31; G2, n = 31; early G1 [<2 h after mitosis], n = 92; and late G1 [>5 h after mitosis], n = 130). (C) Experimental procedure used for the following experiments. Cells were synchronized in early G1, plated on a micropatterned coverslip with 10 different sizes of discs ranging from 500 to 3,500 µm², and serum starved. Bar, 50 µm. (D) G1-starved cells on micropatterns were observed in time-lapse phase-contrast microscopy over 40 h. The proportion of dividing cells (blue), nondividing cells (red), and dying cells (black) were quantified in cells plated on the smallest (500 µm²) and largest (3,500 µm²) micropatterns in the presence (n = 116 and 43, respectively) or absence (n = 123 and 115, respectively) of serum. No clear difference could be observed between the two cell sizes. Bar, 50 µm. (E) Cell quiescence. Cells were plated on micropatterns with or without serum, fixed, and stained for Ki67 (proliferation marker), F-actin (green), and DNA (blue). A large majority of individual cells on small and large micropatterns were quiescent after 24 h of serum starvation, as revealed by their negative Ki67 staining (75%, n = 102; and 79%, n = 174; respectively). Cells proliferated in the presence of serum and were mostly Ki67 positive. Bar, 10 µm.