Stem Cell Proliferation and Quiescence—Two Sides of the Same Coin
A. The red boxed area indicates the population of HSCs. Each cell within this population undergoes cell division with rate s (generating two daughter cells), differentiation with rate d and cell death with rate c, shown by the arrows. The processes of differentiation and cell death lead to the removal of the cell from the HSC compartment. Upon label administration a certain fraction F0 of HSCs gets initially labeled. As N subsequent divisions are necessary to dilute the label below the detection threshold, this can be visualized by a sequence of N compartments named L1 to LN, shown in grey. Cells within theses boxes undergo cell division (transit from Li to Li+1), differentiation, and cell death with the same rates as non-labeled cells. After the Nth division the cells are no longer distinguishable from unlabeled HSCs. B. The population of HSCs is composed of two, subpopulations, indicated by the lower (light green) and upper (dark green) boxes, which differ in their specific rates for cell division (sf and ss), differentiation (df and ds) and cell death (cf and cs). Otherwise, the fast and the slow dividing subpopulations behave identical to the case illustrated in subfigure A. Labeled cells are present in both these subpopulations and need to undergo N subsequent divisions to dilute label below the detection threshold.