Reversible solidification of fission yeast cytoplasm after prolonged nutrient starvation

Cells depend on a highly ordered organization of their content and they must develop strategies to maintain the anisotropic distribution of organelles during periods of nutrient shortage. One of these strategies, observed in bacteria and in yeast cells with acutely interrupted energy production, is to solidify the cytoplasm. Here, we describe a different type of cytoplasm solidification that occurs in fission yeast cells having slowly run out of nutrients after multiple days of culturing. It provides the most profound reversible cytoplasmic solidification of yeast cells described to date. Our data suggest the involvement of a matrix with a certain mesh size that immobilizes cellular components in a size-dependent manner. We provide experimental evidence that cells need time, intrinsic nutrients and intrinsic energy sources to enter this state in the absence of external sources. Such cytoplasmic solidification may provide a robust means to protect cellular architecture in dormant cells.