UCSF

Diffusion in the cytoplasm can greatly impact cellular processes, yet regulation of macromolecular diffusion remains poorly understood. There is increasing evidence that cell size affects the density and macromolecular composition of the cytoplasm. Here, we studied whether cell size affects the diffusion of macromolecules in the cytoplasm in the fission yeast Schizosaccharomyces pombe cells by analyzing the diffusive motions of intracellular genetically-encoded 40nm nanoparticles (cytGEMs). Using cell size mutants, we found that cytGEMs diffusion coefficients decreased in smaller cells and increased in larger cells. To test if these changes in diffusion rates were due to DNA-to-Cytoplasm (DC) ratio, we used cytokinesis mutants to avoid decreasing DC ratio in large multinucleate cells and found that these cells have comparable cytGEMs diffusion as their normal-sized counterparts. In investigating the underlying causes of altered cytGEMs diffusion, we showed that larger cells have lower concentrations of ribosomal proteins. Finally, comparison of the proteomes of large and small cells defined size-specific changes in the proteome composition. These studies demonstrate that cell size is an important parameter in determining the biophysical properties of the cytoplasm.