Lipid Nanotubes as a Model for Highly Curved Cellular Membrane Structures
Cells and their organelles show a variety of membrane morphologies with multiple
submicrometer features, for example, tubules, vesicles, folds and pores. The shape of the
cellular membranes can dynamically change to support a variety of functions, such as cargo
transport, transmission of signals between the cells, cell movement and division. A
convenient route to understanding the complexity of cellular membranes is to study
artificially created lipid bilayer membrane systems. The work presented in this thesis is
focused on highly curved membrane structures in the form of lipid bilayer nanotubes.
Firstly, the shape transformation mechanism for free floating lipid nanotubes was
investigated. Driven by their high curvature energy, nanotubes contract in length and
eventually transform into tubular stomatocyte-like structures. Secondly, diffusion, electric
field and Marangoni-flow-driven modes of transport through lipid nanotubes are described.
Then, an important improvement in the characterization of lipid nanotubes was achieved by
developing a new technique for the measurement of lipid nanotube radii. This technique is
based on monitoring the translocation of a photobleached tube region between two
nanotube-connected vesicles during the growth of a receiving/daughter vesicle. The validity
of this measurement technique was confirmed using super resolution microscopy. In
addition, our technique has proven useful for tracking membrane bending rigidity changes
in response to environmental and compositional alterations, both in cell plasma membranes
and in model vesicle systems. Finally, a microfluidic pipette with a self-confining volume at
the tip was presented. It allows for selectively affecting a chosen cell and accessing
membranes on the single cell level.