Ultrastructural rearrangement of the nucleus in situ during osmotic stress

Abstract text (incl. figure legends and references)

Osmotic stress causes flux of solvent into or out of cells as a result of changing environmental conditions. On second to minute time scale cells respond by adjusting their volume. How cells cope with the mechanical impact and how this process affects cellular ultrastructure remains underexplored.

We combine fluorescence microscopy and electron cryo-tomography to study the structural rearrangements to the cytosolic and nuclear architecture in Dictyostelium discoideum cells during osmotic stress. These cells undergo volume changes that result in changes to the cellular protein concentration, affecting the visibility of protein complexes in the tomogram volume.

We visualize specific changes to nuclear architecture, the organization of regular nuclear filaments upon nuclear shrinkage, as well as changes to the nuclear envelope membrane resulting from osmotic pressure and mechanical forces.

Using subtomogram averaging, we obtain an in situ structure of the nuclear pore complex of D. discoideum and build a corresponding model from AlphaFold predicted structures of its components. D. discoideum nuclear pores have a unique structure compared to other organisms and are subject to dilation and constriction movements under different osmotic stress conditions.