Significance – Many human disease present alterations in nuclear mechanics and morphology across the human disease spectrum (heart disease, muscular dystrophy, aging, cancer, and more). In many of these disease both of the main mechanical components of the cell nucleus are altered, chromatin and lamins. However, at the start of my postdoctoral research, the inability to determine the distinct contributions of these two mechanical components was hindering progress towards understanding the role of altered nuclear mechanics in disease. To overcome this key hurdle I developed a novel force measurement technique to answer this question and provide further insights into the basics of nuclear mechanics. This technique allows, for the first time, force measurement of the whole-nucleus under extensional forces at both short and long strains. Using this novel technique, I revealed that chromatin dominates the short-extension force response (3 um or <30% strain) and lamin A dominates the long-extension force response via strain stiffening.

Video/technique – I developed a novel nucleus isolation and force measurement technique adapted from chromosome micromanipulation techniques pioneered in the Marko lab. In short, a single nucleus is isolated from a living cell via localized lysis, by using a spray of a mild detergent from a micropipette, followed by capture with a second micropipette. Below, the right “pull” micropipette extends the whole nucleus while the deflection of the left “force” micropipette measures force. The force is calculated by the “force” micropipette’s deflection distance multiplied by the premeasured spring constant. At the end of the video, the chromatin within the nucleus is condensed by spraying 10 mM MgCl2 via a third micropipette that is out of view. Chromatin condensation causes nucleus to contract, and the “force” micropipette is further deflected meaning the stiffness of the nucleus increased. This video demonstrates that chromatin is a major mechanical component of the nucleus, which is the focus of my research. Read more about my technique and findings in my first author paper Chromatin and lamin A determine two different mechanical response regimes of the cell nucleus in MBoC.