Noise in Regulatory Networks 3

4 Abstract Gene regulatory networks control the production of the principal functional 5 units (proteins, RNA) in cells. The observation of variability in expression levels 6 within isogenic populations of cells demands an understanding of how this variability 7 changes our understanding of cellular behaviour inferred from bulk measurements. 8 In particular, we focus on simple models of gene expression to identify the key pro9 cesses and their relative durations that determine fluctuation propagation within 10 regulatory networks. We also point out modes of noise reduction and phenotypic 11 state switching that rely on the average dynamics of regulatory networks, as well as on 12 spatial characteristics of their embedding within organisms.