Identification of multiple microtubule initiating sites in mouse neuroblastoma cells.

Mouse neuroblastoma N-18 cells can be induced by serum deprivation to sprout multiple neurite-like processes which contain many microtubules. Mitotic drugs such as colcemid and colchicine depolymerize these microtubules and the cells lose their processes. Reappearance of microtubules after removal of the drugs was followed by immunofluorescence microscopy using tubulin specific antibodies. At early recovery times multiple star-like structures which contained tubulin were detected in the perinuclear are and in the cytoplasm of individual cells. The mean number seen per cell as approximately 5. Their formation preceeded the organization of the complex microtubular networks typical of N-18 cells. The probable action of these structures as microtubular organization centers (MTOCs) is discussed. Multiple structures were detected during recovery from the influence of mitotic drugs both in previously induced and non-induced N-18 cells, suggesting that N-18 cells harbour the potential of formation of multiple organization centers even without previous induction. We discuss the possibility that differentiation of neuroblastoma N-18 cells may require microtubular organization centers.