Reshuffling Overcrowded Milieu: Stress-Induced Reorganization of the Eukaryotic Membrane-Less Organelles.

Cells are crowded entities, but the intracellular space represents an inhomogeneously crowded environment, where the concentrations of macromolecules (proteins, nucleic acids, etc.) are not uniformly distributed throughout the cell resulting in regions with different levels of crowding. Liquid-liquid phase separation (LLPS)-driven formation of various membrane-less organelles (MLOs) represents a means for the control, regulation, and redistribution of cellular crowded environment. Because MLOs contain the high concentrations of biological macromolecules (proteins and RNAs), often significantly exceeding those of the surrounding cytoplasm or nucleoplasm, their inside represents an overcrowded milieu. It is well-known that the appearance of the stress-induced MLOs represents a reaction to various types of stresses, enabling the protection of the genetic and protein material during hostile conditions. However, stress can also cause structural, functional, and compositional changes in the MLOs, which are constitutively present in the cells, thereby causing the reshuffling of the overcrowded environment. This chapter describes stress-induced changes in several MLOs (nucleolus, Cajal bodies, paraspeckles, nuclear speckles, NELF-Bodies, nucleolar stress bodies, PML-bodies, stress-granules, and Р-bodies) found in the eukaryotic cells.