Required for organization of the cellular microtubule array and microtubule anchoring at the centrosome. May regulate microtubule organization at least in part by targeting the microtubule severing protein KATNA1 to the centrosome. Also positively regulates the activity of the minus-end directed microtubule motor protein dynein. May enhance dynein-mediated microtubule sliding by targeting dynein to the microtubule plus ends. Required for several dynein- and microtubule-dependent processes such as the maintenance of Golgi integrity; the centripetal motion of secretory vesicles and the coupling of the nucleus and centrosome. Also required during brain development for the migration of newly formed neurons from the ventricular/subventricular zone toward the cortical plate. Plays a role; together with DISC1; in the regulation of neurite outgrowth. Required for mitosis in some cell types but appears to be dispensible for mitosis in cortical neuronal progenitors; which instead requires NDE1. Facilitates the polymerization of neurofilaments from the individual subunits NEFH and NEFL. {ECO:0000269|PubMed:12796778; ECO:0000269|PubMed:15208636; ECO:0000269|PubMed:15473966; ECO:0000269|PubMed:16107726; ECO:0000269|PubMed:16203747}.