Figure 2. Negative feedback is required for maintenance and regeneration of the equilibrium between CSCs and non-stem cancer cells.

(a) Maintenance of the relatively constant CSC population in cell culture. The cell culture is performed as described in Fig. 1C legend. The percentages of CSCs (CD44⁺CD24⁻ cells) are measured using FACS analysis every two days. (b) Regeneration of the equilibrium between CSCs and non-stem cancer cell. The putative CSCs (CD44⁺CD24⁻ cells) are sorted among MCF-7/HER2 cells by flow cytometry, and then seeded at low density (5 × 10⁴ cells/10 cm plate) in DMEM medium containing 10% FBS. The percentages of CSCs (CD44⁺CD24⁻ cells) are measured using FACS analysis every two days. The data are shown as the means of triplicate experiments. The estimated parameter values for the simulations are given in Table S2.