Figure 1.

Stochasticity of gene expression at different levels. Stochasticity of gene expression in multicellular organisms can be considered at different level of granularity. Defining intrinsic and extrinsic depends on frame of reference. (S1) From a gene-centric view (purple), stochasticity of biochemical processes defines intrinsic expression stochasticity, with all other processes contributing to external stochasticity. (S2) From a cell-centric view (blue), intrinsic stochasticity also includes stochasticity of the regulatory network, metabolite concentration, and autocrine functions. (S3) On the organism level (green), intrinsic includes development, cell–cell, and tissue–tissue communication. (S4) On the population level (red), stochasticity of the environment is intrinsic. In our work, we measured and modeled gene-level expression noise (A) as influenced by extrinsic factors at the remaining levels.