DIAPH3 deficiency links microtubules to mitotic errors, defective neurogenesis, and brain dysfunction

Diaphanous (DIAPH) 3 is a member of the formin proteins that have the capacity to nucleate and elongate actin filaments and therefore, to remodel the cytoskeleton. DIAPH3 is essential for cytokinesis as its dysfunction impairs the contractile ring and produces multinucleated cells. Here, we report that DIAPH3 localizes at the centrosome during mitosis and regulates the assembly and polarity of the mitotic spindle. DIAPH3-deficient cells display disorganized cytoskeleton, multipolar spindles, and supernumerary centrosomes. DIAPH3-deficiency disrupts the expression and/or stability of microtubule-associated proteins SPAG5 and KNSTRN. SPAG5 and DIAPH3 have similar expression patterns in the developing brain and overlapping subcellular localization during mitosis. Knockdown of SPAG5 phenocopies the DIAPH3 deficiency, whereas its overexpression rescues the DIAH3 phenotype. Conditional inactivation of Diaph3 in the cerebral cortex profoundly disrupts neurogenesis depleting cortical progenitors and neurons; and leading to cortical malformation and autistic-like behavior. Our data uncover uncharacterized functions of DIAPH3 and provide evidence that this protein belongs to a molecular toolbox that links microtubule dynamics during mitosis to aneuploidy, cell death, fate determination defects, and cortical malformation.