Noisy production and epigenetic feedback of a cell polarization protein in budding yeast

As gene expression involves interactions between relatively small numbers of molecules, it is prone to fluctuations. Indeed, it has been shown that protein concentrations may vary considerably between cells and within the same cell over time. Although noisy gene expression is often detrimental and selected against by evolution, it can be beneficial in some cases, since it diversifies the population. A mechanism of epigenetic feedback could enhance the positive benefits of noise by allowing lucky individuals to pass on their state to the offspring, bringing about a temporary selective advantage. We investigate this phenomenon in budding yeast by examining population distributions of the cell polarization protein Cdc42. The noisy production of this protein leads to variability in cellular Cdc42 concentrations between cells. In certain genetic backgrounds, lucky cells possessing a high Cdc42 concentration will divide faster than cells with a low concentration. Moreover, their daughter cells should get a head start in their own cell cycle because they partly inherit the Cdc42 concentration from their parents. By measuring and modeling population distributions of Cdc42 in different conditions, we aim to characterize the effects of noisy production and epigenetic feedback on population fitness and the possibility of bridging fitness gaps in the course of evolution.