CDK6/kinase activity is required for Notch-dependent proliferation, survival, and differentiation. (A) Proliferation: the fold change in cell expansion was calculated based on the ratio of cocultured cells at day 12 to total c-Kit⁺Lin⁻ cell number plated at day 0, which were arbitrarily defined as 1 unit. Data are mean ± SE (N = 5). *P < .05, significantly different from the control. (B) Apoptosis profiles after annexin V staining. (C) The percentage of cells stained with annexin V. Data are mean ± SE (N = 5). *P < .05, significantly different from the WT-Δ control. (D) Differentiation of stem cells into T cells. Flow cytometric profiles of thymocytes from day 12 cultures stained with CD4 and CD8 antibodies. The percentage of cells in each quadrant is shown.