From dynamic gene expression noise to static population heterogeneities: The role of stochastic effects in Molecular Biology Seminar

In this talk I will discuss the role of noise in molecular networks within a dynamical systems theory approach. In particular I will focus on relating gene expression noise to the emergence of static heterogeneities in cell populations. I will consider two case studies, namely the emergence of drug tolerant phenotypes in clonal bacterial populations and the realization of different cell types from one single multipotent cell. In the first case, I will introduce a simple model of stochastic gene expression coupled with growth control, and I will show how distinct growth, and hence drug tolerant, phenotypes can emerge as a result of a slowdown of stochastic fluctuations. I will discuss these findings in light of a weak ergodicity breaking phenomenon. In the second case, I will highlight the non-trivial effects that extrinsic noise may have on the cell differentiation process. In particular I will define the noise propagation problem, and discuss in this context the relevance of stochastic systems exhibiting time scale separation between fast and slow variables. These findings suggest a fundamental role played by biological noise with interesting evolutionary implications.