Gene recruitment and adaptive reprogramming of genetic regulatory networks

Erez Braun
Technion

Understanding the dynamics of genetic regulatory networks requires long-term experiments at the level of cell populations. We discuss chemostat experiments where the metabolic and regulatory dynamics of yeast populations are continuously measured over long time scales under stable environmental conditions. The recruitment of a gene to a foreign regulatory system is a major evolutionary event that can lead to novel phenotypes. The evolutionary potential of the cells depends on their ability to cope with challenges presented by gene recruitment. We study the population dynamics following a gene recruitment event. The experiments show that the regulatory system reprogrammed to adaptively tune the expression of the recruited gene, even though it was detached from its natural feedbacks. The adapted state was maintained for hundreds of generations in various environments. The time scales involved and the reproducibility of separate experiments render spontaneous mutations an unlikely underlying mechanism. Essentially all cells could adapt, excluding selection over a genetically variable population. Overall, the results reveal environmentally-induced, heritable adaptation allowing the cells to overcome the strong challenge imposed by the recruitment event. The experiments demonstrate the plasticity of genetic regulatory networks (by detailed analysis of expression arrays along the adaptation trajectory) and their potential to support highly demanding events of gene recruitment.