Deciphering intracellular and nuclear mechanics with frequency and time domain optical tweezer assays

Cells sense mechanical forces in various biological processes that are relevant to the development, homeostasis, and aging of organisms. Although the cell surface has been extensively studied as a cellular mechanosensing structure, intracellular organelles, particularly the nucleus, are now also recognized as a cellular mechanogauge. Nonetheless, there are still significant gaps in our understanding how the mechanical properties of intracellular organelles and the cytoplasm affect mechanical force transmission and cellular mechanosensing. Towards this goal, we developed and deployed a new active microrheology routine based on a time-shared laser source to measure stress and strain of the cytoplasm, nuclear envelope, and nucleoplasm directly inside zebrafish progenitor cells as a model system. We call this method, Time-Shared Optical Tweezer Microrheology (TimSOM). In addition, we developed a dual optical trap assays to investigate nuclear stability and intranuclear calcium dynamics to understand how the nucleus reacts and responds to mechanical stresses. Our results suggest that nuclear position and stress dissipation is achieved by the joint action of actin and tubulin cytoskeleton, integrated with the LINC complex, which highlights the importance of intracellular mechanics for cellular behavior and cellular mechanotransduction.