From Nuclei to Artificial Cells: Probing the Mechanics of Minimal Systems

Abstract

The creation and development of a self-sustaining synthetic cell are intimately linked to the presence of a membrane cortex and an internal polymeric skeleton, as these are essential for maintenance of its shape as well as sustaining external loads. Thus, understanding the mechanics of natural cortex systems will be a fundamental step towards building a functioning synthetic cell. Therefore, we aim to investigate the mechanics of isolated nuclei as simple biological systems, which can be modelled as a cortical shell enclosing a crosslinked polymeric core. To this end, we employ a combination of Optical Tweezers (OT) and Acoustic Force Spectroscopy (AFS); while the former allows highly controlled manipulation and sensitive force-detection, AFS enables multiplexing and high force measurements. In particular, optical tweezers are used to apply pN forces to the samples by using Poly-L-lysine coated microspheres as handles, while AFS enables the application of forces up to 15 nN to surface-attached nuclei. The complementarity of the two techniques allows us to explore nuclear mechanics across a wide range of forces and loading rates, as well as in different experimental settings (e.g. force ramps, clamps or oscillatory stress measurements). Upon application of force ramps, nuclei respond viscoelastically and are observed to strain stiffen at large deformations, possibly due to recruitment of specific nuclear components (e.g. the nuclear lamina). Moreover, stretched nuclei exhibit hysteresis when returning to the initial length, while subsequent pullings on the same nucleus do not alter its force response.The data thus obtained is then modelled and reveals how the individual structural components of nuclei contribute to their mechanical resilience. As there are numerous examples of pathologies characterised by altered nuclear mechanics, our work will help to shed light on how this might occur.