Direct mechanical communication of cellular to nuclear shape in oocytes

Abstract

The mechanical properties of the cytoplasm and nucleoplasm are crucial for the correct and robust functioning of a cell and play a key role in understanding how mechanical signals are transferred to the nucleus. Here, we demonstrate remarkable shape mimicry between the cellular and nuclear shape of oocytes, following the externally applied deformation without direct contact between the cell cortex and the nucleus. This effect arises from a surprisingly soft and fluid-like nucleoplasm that is barely resisting any external strain, while the viscoelastic cytoplasm drives shape transmission. Comparative studies in jellyfish, starfish, and mouse oocytes reveal that lower cytoplasmic elasticity in jellyfish leads to reduced nuclear shape mimicry, highlighting the role of cytoplasmic mechanics in nuclear deformation. Significance StatementMechanosensing of the nucleus is, in addition to chemical signalling, an important factor in gene expression. Although nuclei are often thought to be rigid inclusions in the cytoplasm of a cell, we show that in oocytes nuclei are much more deformable. Using a combination of intranuclear, intracellular and extracellular measurements, we attribute our findings to a fine balance between the soft nucleoplasm surrounded by an elastic shell and the viscoelastic properties of the cytoplasm.