Manipulation and Probing of Cell Nucleus at the Micro- and Nanoscale Uncovers a Potential Role of beta-Actin in Nuclear Biomechanics

Atomic force microscopy (AFM) is a crucial instrument for probing and manipulating surfaces, soft matter, and objects at micrometer and nanometer scales. Furthermore, AFM procedures offer unparalleled opportunities to deepen our understanding of cells, cellular components, cellular processes, and genetics. The nuclear beta-actin (beta-actin) pool plays an essential role in diverse nuclear processes, including chromatin and transcription regulation, and these mechanisms affect key cellular processes such as DNA damage response and cell differentiation. We recently revealed, using AFM, that the composition of endogenous beta-actin levels directly impacts biomechanical and biophysical features of cell membrane surface, and as well, cellular behavior in 2D and 3D cultures, thus leading to global chromatin changes in mouse embryonic fibroblasts (MEFs). In this work, we are further investigating whether the beta-actin isoform is also involved in regulating biomechanical properties of isolated nucleus of MEFs, including the elasticity and bio-adhesiveness. By employing AFM-based probing and manipulation procedures on individual nuclei with different genotypes, we observed that the elasticity is reduced in the nuclei lacking beta-actin. Additionally, there was an apparent decrease in surface tether forces. Notably, re-introduction of beta-actin through genetic manipulation restores elasticity and other biomechanical properties towards the original wild-type nuclei. Combining findings of this work with deep-sequencing will help in revealing the essential role of beta-actin in the global chromatin organization and its regulatory relationship with nuclear biomechanics. This work demonstrates the power of combining AFM probing and manipulation with genetic modification for studying cellular components and processes.