Casein kinase 1α essentially regulates thrombopoiesis by driving megakaryocyte maturation and cytoskeleton organization.

Throughout thrombopoiesis megakaryocytes (MKs) form proplatelets within the bone marrow (BM) and release platelets into BM sinusoids. Casein kinase 1α (CK1α) is a major player and thus, an important therapeutic target in several hematological malignancies. This study aimed to define the role of CK1α for the essential steps of thrombopoiesis and to dissect potential mechanisms of thrombocytopenia. MK-specific CK1α-deficiency resulted in a macrothrombocytopenia. Ck1αPf4Δ/Pf4Δ mice displayed a substantial BM hyperplasia with pivotal changes in MK nuclear lobulation and reduced contact to BM sinusoids. Ck1αPf4Δ/Pf4Δ MKs displayed a defective cytoskeleton organization reflected by a decreased amount of polymerized filamentous actin and disturbed microtubule dynamics due to p21/p53 accumulation and impaired Rho-associated protein kinase (ROCK)/LIM domain kinase (LIMK)/cofilin signaling. Further, pronounced defects in DMS (demarcation membrane system) polarization and proplatelet formation of Ck1αPf4Δ/Pf4Δ MKs, unraveled CK1α as a prerequisite for thrombopoiesis. Our findings could be translated into a human approach, because a CRISPR/Cas9-mediated genetic deletion of CSNK1A1 in MKs derived from human CD34+ progenitor cells resulted in a substantial defect in human MK maturation and platelet production. The present observations elucidated CK1α as an important signaling molecule in MK cytoskeletal dynamics and polarization, proplatelet formation, and polyploidization, thus highlighting the crucial role of CK1α in platelet biogenesis.