Synaptically coupled central nervous system neurons lack centrosomal gamma-tubulin.

In cycling cells, microtubule assembly is initiated at the centrosome and requires the centrosomal protein gamma-tubulin. Previously, it was reported that gamma-tubulin is present at the centrosome of cervical ganglion cells undergoing axonal growth, but not in the axons or dendrites. We find that although gamma-tubulin is present at the centrosomes of neurons just beginning to extend processes, it is not associated with centrosomes in hypothalamic and cortical neurons on which functional synaptic connections have formed. In contrast, another centrosomal protein, pericentrin, is associated with the centrosome at all stages. These results suggest that centrosomal microtubule nucleation is required for early stages of neurogenesis to supply sufficient microtubule polymer to support rapid axonal growth, but is not required for maintenance of axonal microtubules in synaptically coupled neurons.