A chance-selection model for cell differentiation

A chance-selection model is proposed to explain cell differentiation. It is based on the general idea that stochasticity at the molecular level generates diversity in cell types whereas cell interactions impose a characteristic order on the developing embryo. In this model, gene expression depends on stochastic molecular interactions between transcriptional regulators and DNA. Random diffusion of these regulators along DNA causes differential gene expression in differentiating cells.The role of phosphorylation or dephosphorylation of transcriptional regulators, triggered by cell interactions, is to control their random diffusion and to stabilize stochastic gene expression in differentiated cells. This model is based on well documented phenomena: random diffusion of DNA binding molecules along DNA, phosphorylation or dephosphorylation of transcription factors by protein kinases or phosphatases and control of DNA binding of transcription factors through this latter process. The different explanatory powers of deterministic and stochastic models are discussed.