Using atomic force microscopy to measure the nanomechanical properties of cell nuclei and clathrin cages : an odyssey towards the nano-world

Abstract

This thesis presents how mechanical measurements with atomic force microscopy in combination with finite element analysis were used to increase our understanding of the functioning of sub-cellular biological assemblies. Clathrin proteins are known for their ability to form curved lattices that play an essential role in the bending of, and transport across, the cell membrane. Force spectroscopy experiments on isolated and reconstituted model systems revealed that the lattice mechanics can be regulated by several binding factors. This finding suggests that besides chemical signals, mechanical regulation can play an important role in biological processes. The cell nucleus is a complex structure consisting of DNA and various proteins enclosed in the nuclear membrane. Although there is evidence that mechanical stimuli affect gene expression it remains largely unclear how forces are transduced through the nucleus. Micro-rheology measurements showed a non-homogeneous distribution of elasticity and viscosity in the nucleus which provides an explanation why some nuclear regions are more active in gene transcription than others. Besides the biological findings, this work describes multiple technological advances that were essential to perform the measurements. These include methods to calibrate the stiffness of atomic force microscopy cantilevers with interferometry, to perform high bandwidth micro-rheology while staining the nucleus, and to perform 3D image reconstruction with optical microscopy during mechanical measurements.