Post-Translational Polymodification of β1 Tubulin Regulates Motor Protein Localisation in Platelet Production and Function

In specialised cells, the expression of specific tubulin isoforms and their subsequent post-translational modifications drive and coordinate unique morphologies and behaviours. The mechanisms by which β1 tubulin, the platelet and megakaryocyte lineage restricted tubulin isoform, drives platelet production and function remains poorly understood. We investigated the roles of two key post-translational polymodifications (polyglutamylation and polyglycylation) on these processes using a cohort of thrombocytopenic patients, human induced pluripotent stem cell (iPSC) derived megakaryocytes, and healthy human donor platelets. We find distinct patterns of polymodification in megakaryocytes and platelets, mediated by the cell specific expression of effecting (Tubulin Tyrosine Ligase Like - TTLL) and reversing (Cytosolic Carboxypeptidase - CCP) enzymes. The resulting microtubule patterning spatially regulates motor proteins to drive proplatelet formation in megakaryocytes, and the cytoskeletal reorganisation required for thrombus formation. This work is the first to show a reversible system of polymodification by which different cell specific functions are achieved.