Spatial allocation rules governing systems-level organelle biogenesis

Uncovering the functional rules by which the eukaryotic cell controls the size of its organelles is a fundamental problem in cellular biophysics. Here we aim to elucidate one such rule, namely how the budding yeast Saccharomyces cerevisiaecoordinates the size of its organelles with the size of the cytoplasm within which they reside. By combining quantitative fluorescence microscopy with tools from synthetic cell biology, namely an artificial biomolecular condensate derived from the bacterium Escherichia coli, we directly engineer cells to exhibit a wide range of cytoplasmic spatial availability and monitor the response of organelle size to varying spatial constraints. In contrast to the mitochondria, lipid droplets, and endoplasmic reticulum, we observe that vacuolar sizes exhibit a strong response to decreasing cytoplasmic availability. We observe that with a significant amount of condensate in cells, the vacuolar volume starts to decrease as cell size increases, the opposite relationship to what is observed in the cells with an insignificant amount of condensate and previously reported observations. Our data suggest the hypothesis that the cell actively controls the volume of available cytoplasm even as the size of the cell as a whole changes and that the vacuole potentially plays a key role in buffering variation in cytoplasmic volume.