Interplay of chromatin and cytoskeleton in regulating nuclear size, shape, and mechanics

Mechanical stress is a constant in the cellular environment. External forces are rapidly propagated to the nucleus, causing it to deform. The ability of nuclei to deform under load are determined by its mechanical properties – including its shape, size and stiffness, which can be tuned in response to physical cues from the environment. While the nuclear lamina is a known contributor to nuclear mechanics, the role of chromatin remains incompletely understood. We developed a method to apply piconewton-range forces to isolated nuclei using optically-trapped beads. Using a force-feedback system, we precisely apply a constant amount of force and record deformation over time, allowing for quantification of mechanical and material properties of the nucleus. We use this method to quantify how changes in chromatin condensation, induced by altering histone methylation and histone acetylation levels, affect nuclear mechanics. Additionally, we determine how chromatin condensation impairs nuclear size and shape in whole cells, and we show how chromatin condensation and the cytoskeleton interplay to dynamically regulate nuclear size and shape.