Microtubules in Motion: dynamics and diversity of the microtubule cytoskeleton

Abstract

During many years of research, the core components and mechanisms required to build a microtubule array have been identified and the basic traffic rules that apply to motor proteins navigating this microtubule network have been unraveled. A key remaining challenge is to understand how all these different components interact in intact and specialized cells to form a functional transport system. This thesis investigates how within cells a specialized microtubule array is formed, organized, and diversified for efficient navigation by motor proteins. Formation of a specialized microtubule array: In chapter 2, we unravel a novel cytoskeletal mechanism for neuronal polarization. We show that in developing neurons, axon specification is determined by differences in microtubule network mobility between neurites under the control of extracellular (mechanical) cues and intracellular signaling by Rho-GTPases. Organization of an interphase microtubule array: In chapter 3, we show that Kinesin-1 and Dynein contribute to the organization of the interphase microtubule network by driving microtubule motility, -positioning and -turnover. Visualizing microtubule diversity in living cells: In chapter 4, we introduce and validate a live-cell marker for stable microtubules: StableMARK. We use this new tool to study the properties of stable microtubules in living cells and visualize the spatiotemporal changes in the stable microtubule array throughout the cell cycle. Structural features underlying microtubule diversity: In chapter 5, we combine the power of light- and electron microscopy to study diversity in microtubule lattice spacing in intact cells. We show that most microtubules within cells have a compacted lattice, yet a subpopulation of microtubules has an expanded lattice configuration. Furthermore, we demonstrate using StableMARK that stable microtubules have an expanded lattice in situ. In chapter 6, I discuss the findings presented in chapter 2-4 in light of the overall question of this thesis: how is an efficient cellular transport system built and maintained? In addition, some preliminary data regarding this question will presented and discussed