Heterogeneity among microtubules of the cytoplasmic microtubule complex detected by a monoclonal antibody to alpha tubulin.

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Abstract
Three monoclonal antibodies specific for tubulin were tested by indirect immunofluorescence for their ability to stain cytoplasmic microtubules of mouse and human fibroblastic cells. Double label immunofluorescence was used to compare the staining patterns of these antibodies with the total microtubule complex in the same cells that were stained with a polyclonal rabbit antiserum reagent. Two of the monoclonal antitubulin antibodies bound to all of the cytoplasmic microtubules but Ab 1-6.1 bound only a subset of cytoplasmic microtubules within individual fixed cells. Differential staining patterns were observed under various fixation conditions and staining protocols, in detergent-extracted cytoskeletons as well as in whole fixed cells. At least 1 physiologically defined subset of cytoplasmic microtubules, those remaining cells pretreated for 1 h with 5 .mu.M colcemid, appeared to consist entirely of Ab 1-6.1 positive microtubules. The same was not true of the microtubules that remained in either cold-treated cells or in cells that were exposed to hypotonic medium. The demonstration of antigenic differences among microtubules within single fixed cells and the apparent correlation of this antigenic difference with at least 1 physiologically defined subset suggests that mechanisms exist for the differential assembly or postassembly modification of individual microtubules in vivo, which may endow them with different physical or functional properties.