In This Issue

Stem cell populations continually regulate cell division, growth, and death to sustain regeneration throughout the lifetime of an organ or tissue. The mechanisms of self-regulation, however, are unclear. Jinzhi Lei et al. (pp. E880–E887) modeled three stem cell processes: differentiation, proliferation, and cell death or apoptosis. The model, which is based on population biology, generates stem cells with a distribution of epigenetic states and requires the cell population to maximize cell performance after each cell division. The authors found that heterogeneous proliferation of stem cells, dependent on the epigenetic state of the parent cell, leads to balanced populations that are able to respond robustly to sudden changes in the stem cell system. Allowing genetic mutation in the model induces the population to evolve apoptosis regulation to maximize cell performance during homeostasis. The results suggest that stem cell regulation processes are active both over a single cell division cycle and over the lifetime of a tissue, and that heterogeneous proliferation, in which cells possess variable probabilities of proliferation, increases the overall robustness of the stem cell population, according to the authors. — P.G.