Stem cell homeostasis regulated by hierarchy and neutral competition

Abstract

Tissue stem cells maintain themselves through self-renewal while constantly supplying differentiating cells. As a mechanism of stem cell homeostasis, two distinct models were proposed: the classical model states that there are hierarchy among stem cells and master stem cells provide stem cells by asymmetric divisions, whereas the recent model states that stem cells are equipotent and neutrally competing each other. However, its mechanism is still controversial in several tissues and species. Here, we developed a mathematical model linking these two models. Our theoretical analysis showed that the model with the hierarchy and neutral competition, called the hierarchical neutral competition (hNC) model, exhibited bursts in clonal expansion, unlike existing models. Furthermore, the scaling law in clone size distribution, thought to be a unique characteristic of the recent model, was satisfied in the hNC model. Based on these findings, we proposed a criterion for distinguishing the three models by experiments.