New tools reveal interaction determinants and post-mitotic function of crucial microtubule regulators
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Microtubules are a major constituent of the cytoskeleton in all eukaryotic cells. They are essential for cell morphogenesis and motility. Specifically in the dividing cells, microtubules form the spindle which segregates chromosomes. Microtubule plus ends constantly switch between phases of growth and shrinkage which is necessary for microtubule reorganization and thus their function. Importantly, microtubule dynamics are highly regulated by microtubule-associated proteins (MAPs). EB1 and Mini spindles (Msps) are unique amongst MAPs because they bind and track growing microtubule plus ends autonomously. Although essential for cell division and thus highly expressed in dividing cells, EB1 and Msps are also abundant in differentiated cells. However, to identify post-mitotic roles of proteins essential for cell division, particularly in context of a multicellular organism, is a challenge requiring new tools which I aimed to develop in my project. Since EB1 acts by recruiting MAPs to the microtubule plus ends, I generated short peptides which bind to Drosophila EB1 to block interactions with these MAPs. I showed that an EB1-MAP interaction was disturbed in Drosophila S2 cultured cells and expressing these peptides in developing Drosophila reduced fly viability. Further screening and analysis of peptides interacting with fly EB1 and its human homologues uncovered sequence determinants promoting strong binding and specificity. To uncover Msps function, I generated a msps temperature sensitive mutant and found that Msps is essential for neuromuscular function in developing Drosophila. This study showed that the regulation of microtubule dynamics has crucial functions at the whole organism level. These new tools allow the roles of microtubule regulation to be dissected in developing organisms.