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.