Lipid Nanotubes as a Model for Highly Curved Cellular Membrane Structures

Abstract

Cells and their organelles show a variety of membrane morphologies with multiplesubmicrometer features, for example, tubules, vesicles, folds and pores. The shape of thecellular membranes can dynamically change to support a variety of functions, such as cargotransport, transmission of signals between the cells, cell movement and division. Aconvenient route to understanding the complexity of cellular membranes is to studyartificially created lipid bilayer membrane systems. The work presented in this thesis isfocused on highly curved membrane structures in the form of lipid bilayer nanotubes.Firstly, the shape transformation mechanism for free floating lipid nanotubes wasinvestigated. Driven by their high curvature energy, nanotubes contract in length andeventually transform into tubular stomatocyte-like structures. Secondly, diffusion, electricfield and Marangoni-flow-driven modes of transport through lipid nanotubes are described.Then, an important improvement in the characterization of lipid nanotubes was achieved bydeveloping a new technique for the measurement of lipid nanotube radii. This technique isbased on monitoring the translocation of a photobleached tube region between twonanotube-connected vesicles during the growth of a receiving/daughter vesicle. The validityof this measurement technique was confirmed using super resolution microscopy. Inaddition, our technique has proven useful for tracking membrane bending rigidity changesin response to environmental and compositional alterations, both in cell plasma membranesand in model vesicle systems. Finally, a microfluidic pipette with a self-confining volume atthe tip was presented. It allows for selectively affecting a chosen cell and accessingmembranes on the single cell level