Expanding views on microtubule organization in cycling and differentiated cells

Our body is composed of cell types with various functions and forms; ranging from small round immune cells, to neurons with long signal-transmitting arms and lung cells with whipping hair-like protrusions. These cellular architectures are established and maintained by the skeleton within a cell. One of the components of the ‘cytoskeleton’ are microtubules, dynamic intracellular filaments which organize into arrays to collectively perform essential cellular functions. Despite the broad functional diversity of microtubules, most current knowledge has been derived from two-dimensional, non-specialized cell culture systems. Consequently, little is known about microtubule organization and function in specialized cell types within our body. The aim of this thesis was to compare cellular organization in cycling and differentiated cells, with the focus on the microtubule network. To visualize the very small, micrometer long microtubules and their organizing center in three-dimensions we used a recently developed super-resolution technique, Expansion Microscopy, which physically expands the sample up to ten-fold. Hereby, the imaging resolution is increased dramatically compared to regular light-microscopy techniques which results in unpreceded image quality and micrometer detail which allowed us to visualize the three-dimensional architecture of physiologically relevant cell types, which was impossible before. Our findings demonstrate that, compared to cycling cells, lung epithelial cells possess a more complex microtubule architecture composed of multiple distinct arrays, while their organizing centers display reduced complexity. This may reflect a general principle; during differentiation, as the primary cellular function shifts from proliferation to tissue maintenance, centrosomal complexity decreases while the complexity of microtubule arrays increases.