FIGURE 8:

Cytoplasm compaction and compartmentalization is a protective state for energy-depleted cells. Ultrastructural analysis shows that energy depletion induces a massive reorganization of cytoplasmic structures in yeast cells. ATP-depleted cells undergo cell volume reduction, with consequent formation of plasma membrane invaginations (1) and a pronounced increase in macromolecular crowding (2). Numerous membraneless compartments of amorphous (3) or highly ordered morphologies, such as eIF2B filaments and bundles (4), appear in the cytoplasm. Energy-depleted cells are also characterized by the fragmentation of lipid droplets, suggesting a switch to β-oxidative metabolism of fatty acids. All these cellular rearrangements result in a “solidification” of the cytoplasm that could functio¡n as a protective mechanism for molecular components, preserving them to be readily available when favorable environmental conditions are restored.