Unequal cell division as a driving force during differentiation.

Unequal cell division, leading to daughter cells of different sizes, is a common event during development. We have formulated a model that shows how different cell sizes can lead to significant differences in the expression of an activator gene. The model is based on well-known aspects of the regulation of gene expression, specifically the existence of multiple regulatory sites, positive autoregulation, and the short half-life of regulatory proteins. Thus the daughter cells may follow distinct differentiation pathways even if there were no localized determinants in the mother cell.