Differential pathways of recruitment for centrosomal antigens to the mitotic poles during bipolar spindle formation

As cells enter mitosis, centrosomes undergo many transformations and become associated with different molecules in a stage-specific manner. We have developed a protocol for immunofluorescence staining with four antibody probes that can help us to follow the interaction of centrosomal components during mitosis. The cells were first stained with a human autoimmune serum (5051); a monoclonal antiphosphocentrosomal antibody (CHO3); and an antitubulin antibody. Localization of the antibodies was detected using rhodamine-, fluorescein- and AMCA-conjugated second antibodies, respectively. After photographing marked mitotic cells, coverslips were soaked with 0.2 M glycine-HCl at pH 1.0 for 1h to release all antibodies bound to the structures. The same cells were re-stained with a human autoantibody (SP-H) specific for spindle poles and a fluorescein-conjugated second antibody. This allowed us to compare the subcellular distribution of three kinds of centrosomal antigens in a single cell. Mitotic PtK₁ cells treated with either nocodazole or taxol included microtubule-containing cytoplasmic foci and parallel bundles of short microtubules at the cell periphery. All the centrosomal antibodies stained the same one or two dots corresponding to structures labeled by the tubulin antibody. CHO3 also revealed extra cytoplasmic foci, whereas the SP-H antigen was additionally localized at one end of the free microtubule bundles. As the microtubules reorganized into bipolar spindles during the recovery from drug treatment, the CHO3 and SP-H antigens coalesced into the spindle poles where the 5051 antigen was located, suggesting that centrosomal antigens become associated with spindle poles through very different recruitment pathways.