טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentElad Stolovicki
SubjectAdaptation and Gene Regulation in Yeast Populations
DepartmentDepartment of Physics
Supervisor Full Professor Braun Erez


Abstract

            Since the beginning of evolution studies scientists searched for explanation for the ways organisms adapt and evolve through complex environmental challenges. Information contained in the DNA sequence (genetic) has an important role in an organism's ability to cope with evolutionary pressures but there are other important mechanisms involve with evolution. The ways gene regulation mechanisms contribute to adaptation of the organism to changes in the environment is still an open question. This work examines the evolvability potential of gene regulatory networks in two major aspects: first, the ability of cells to cope with rewiring of their gene regulation network (like in gene recruitment) and second, the capability of the regulation network to learn and adapt to different environmental conditions.  

The recruitment of a gene to a foreign regulatory system is a major evolutionary event that can lead to novel phenotypes. However, the evolvability potential of cells depends on their ability to cope with challenges presented by gene recruitment events. To study cellular responses to such events, we combined synthetic gene recruitment with a continuous culture and online measurement system. The gene HIS3 from the histidine synthesis pathway was recruited to the GAL system, responsible for galactose utilization in the yeast S. cerevisiae. We show that following a switch from galactose to glucose from induced to repressed conditions of the GAL system in histidine-lacking chemostats (where the recruited HIS3 is essential), the regulatory system reprogrammed to adaptively tune the HIS3 expression, allowing the cells to grow competitively in pure glucose. The adapted state was maintained over hundreds of generations in various environments. These results demonstrate that genetic regulatory networks have the potential to support highly demanding events of gene recruitment.