Metabolic communication between individual yeast cells

Abstract: With the recent progress in sensitive cell manipulation and microfabrication techniques, glycolytic oscillations in yeast have been observed at a single-cell level. It was shown that individually, oscillating cells could entrain their phases by periodic external perturbations. However, the mechanisms by which individual cells communicate to couple their glycolytic cycles within a heterogenic population remained an open question. The aims of the studies presented in this thesis focused on addressing the spatio-temporal dynamics present in the transitions from uncorrelated behavior of individual cells, to the emergence of synchronized subpopulations and traveling waves. In this work, it is reported the design, simulation and fabrication of microfluidic systems that allowed for the environmental control and experimental observation of glycolytic synchronization between individual yeast cells. Optical tweezers (for positioning), together with custom made microfluidic devices, were implemented to induce glycolytic oscillations in monolayered yeast cell arrangements. The developed diffusion-based chambers guaranteed the quasi-static conditions required for the intercellular exchange of chemical mediators. Subsequent image and signal processing, together with graph theory, served the purpose of evaluating the degree of synchrony among individual cells and the spatio-temporal distribution of the coupling. This study shows that synchronization communities are formed depending on the exposure ratios of cyanide and glucose, and the exchanged acetaldehyde. Moreover, those communities are also defined depending on the cell location in the monolayer. The relative phase delays between the glycolytic oscillations from different communities revealed the formation of glycolytic synchronization waves, which can overcome the existing heterogeneity in the system. The results presented in this work contribute to a further understanding on the experimental conditions required to achieve glycolytic synchronization in yeast for single-cell level studies. Furthermore, the spatio temporal characterization of the single-cell responses during cell-cell chemical interactions, explains the formation of traveling waves as a mechanism for glycolytic synchronization. These results, and the developed methodology, can be further optimized and extrapolated to study more complicated cell systems such as the pancreatic  -cells, and the role of metabolic synchronization in the coordinated insulin secretion from the pancreas.