Microtubule Associated Protein Oligomerization on the Microtubule Generates New Functionalities

• Main Author: Tan, Ruensern
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Biochemistry; Biology; Biophysics
• ISBN: 1085740048; 9781085740043

Microtubules (MT) are essential cytoskeletal components for all eukaryotic cell survival. They are both passive and active participants in all cellular processes ranging from intracellular trafficking to cell division. Microtubule associated proteins (MAP) regulate MT dynamics and contribute to the wide array of activities on the MT. The work presented within identifies a gain of function phenomenon for two MAPs, cytoplasmic dynein and tau, that results from self-association on the MT in loosely defined accumulations.Cytoplasmic dynein-1 is a minus-end directed motor protein that transports cargo over long distances and organizes the intracellular MT network. How dynein motor activity is harnessed for these diverse functions remains unknown. Here, we have uncovered a mechanism for how processive dynein-dynactin complexes drive MT-MT sliding, reorganization, and focusing, activities required for mitotic spindle assembly. We find that motors cooperatively accumulate, in limited numbers, at MT minus-ends. Minus-end accumulations drive MT-MT sliding, independent of MT orientation, resulting in the clustering of MT minus-ends. At a mesoscale level, activated dynein-dynactin drives the formation and coalescence of MT asters. Macroscopically, dynein-dynactin activity leads to bulk contraction of millimeter-scale MT networks, suggesting that minus-end accumulations of motors produce network scale contractile stresses. Our data provide a model for how localized dynein activity is harnessed by cells to produce contractile stresses within the cytoskeleton, for example during mitotic spindle assembly.Tau is an abundant microtubule-associated protein in neurons. Tau aggregation into insoluble fibrils is a hallmark of Alzheimer's disease and other dementias, yet the physiological state of tau molecules within cells remains unclear. Using single molecule imaging, we directly observe that the microtubule lattice regulates reversible tau self-association, leading to dynamic condensation of tau molecules on the microtubule surface. Tau condensates form selectively permissible barriers, spatially regulating the activity of MT severing enzymes and the movement of molecular motors through their boundaries. We propose that reversible self-association of tau molecules, controlled by the microtubule, is an important mechanism of tau's biological functions, and that oligomerization of tau is a common property shared between the physiological and disease forms of the molecule.