Synthetic Genetic Circuits: Plasticity and Robustness

Living organisms have evolved to survive in a multitude of environmental conditions. This plasticity, and the robustness to environmental fluctuations, is achieved by altering gene expression levels in response to perturbations while maintaining the basic processes essential for survival. Genetic circuits, which are networks of interacting genes, are responsible for carrying out both the basic processes to sustain life, such as counting time, as well as the specific processes that provide them with adaptability to various environmental conditions while maintaining homeostasis. Gene expression and its regulation are dynamic, stochastic processes. Namely, although gene expression was previously considered to be identical in cells arising from common ancestors, the observation of multiple, single cells expressing fluorescent proteins has shown that gene expression is noisy, which allows genetically identical cells in a homogeneous environment to behave differently, a phenomenon known as cell-to-cell phenotypic variability. Noise in gene expression arises from the fact that most of the underlying biochemical reactions involve small molecular numbers, which leads to infrequent, to some extent random in time, interactions and processes. While initiall