Intracellular particle transport: life in crowded and active networks
Final Report Abstract
There is a long-standing interest shared by cell biologists and biophysicists in unravelling the physical mechanisms of particle transport in cells. My project centred around the question how cellular cytoplasm inuences the diffusive transport of tracer particles. This question has been difficult to address due to the molecular complexity of cells and a lack of experimental techniques that are capable of probing intracellular transport over a wide enough range of length and time scales. Here I proposed to overcome these two hurdles by combining biomimetic cytoskeletal model systems pioneered by the host lab with a novel measurement technique known as Differential Dynamic Microscopy (DDM) that I successfully extended to dense colloidal systems during my PhD. The biomimetic model system mimics two key properties of the actin cytoskeleton in cells: steric hindrance and (active) viscoelasticity of the material. To probe the dynamics of the networks and embedded tracer particles, I performed DDM measurements. The basic concept is time-lapse imaging by confocal uorescence microscopy, followed by image analysis using concepts of light-scattering. DDM provides a window on molecular and particle dynamics over a much wider range of time and length scales than traditional measurement techniques such as particle tracking. During my PhD I demonstrated that DDM is uniquely suited for measuring anomalous dynamics in crowded colloidal systems. Now I extended the technique for the first time to biologically relevant systems. I showed that viscoelasticity, as well as architecture of the surrounded network, could lead to the length-scale dependency of the tracer dynamics. Therefore, the characterization of dynamics at a broad range of time and length scales is essential and paramount to studying anomalous transport phenomena. By performing correlated measurements of the dynamics of the individual network constituents (actin laments) and tracer particles, it will be possible to disentangle the relation between the network viscoelasticity (and further activities) and constrained transport of the tracers. My proof-of-principle measurements are the first step in this direction. This interdisciplinary project at the interface between soft matter physics and cell biology is thus providing a predictive framework to understand the impact of passive and active physical properties of the cytoskeleton on diffusive motion of tracer particles in the cell. In summary, this project will extend our understanding how cells regulate intracellular particle transport.
