Analyzing the role of chromatin compaction in nuclear mechanics, structure, and function

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The nucleus is the organelle which must properly transduce or resist biophysical forces to dictate the spatial organization of the genome and to control mechanotransduction, factors which determine the expression profile of the cell. The two major contributors to nuclear mechanics are lamins, intermediate filaments lining the inner nuclear envelope, and chromatin, which fills the nucleus. Alteration of lamins and chromatin compaction occur in many major human diseases and during healthy cell differentiation. In both cases nuclear, cell, and tissue mechanics and morphology can change drastically. Currently, the mechanistic basis for both disease-based nuclear blebs and healthy differentiation-based changes in nuclear morphology and mechanics is unknown. My studies found that chromatin and its histone-mediated compaction state and cross-linking dictated initial force response (< 30% strain) and morphology while also contributing as a secondary factor to the lamin A dictated strain stiffening at longer deformations. I first propose to use my developed microdissection, micromanipulation, and nanonewton-level force measurement approach to further elucidate the role of nuclear mechanics in genome organization. During nuclear stretching experiments I will determine how the chromatin responds to nuclear deformation through imaging single chromosome loci (CRISPR labeling) and overall chromatin nano-structure. Second, I will investigate the functional impact of the disease-relevant phenotype of nuclear blebbing and rupture that can be caused or suppressed by chromatin-based nuclear mechanics. I will determine if nuclear blebs are a symptom or a cause of disease, via live cell imaging and biochemical techniques to assay for systemic DNA damage, proper transcription, and faithful segregation of genomic content in the bleb. Finally, I will use the well-established primary cell model of keratinocytes to investigate the basis of nuclear morphology changes during differentiation, progenitor to terminal, and loss of homeostasis upon Ras activation to mimic cancer transition. Overall, I aim to develop an independent career investigating the mechanical basis of morphology changes observed for more than 70 years in both disease and in healthy cell differentiation.