Cytoplasmic microtubules in normal and transformed cells in culture: analysis by tubulin antibody immunofluorescence.

Monospecific antibody directed against bovine brain tubulin was used as an immunofluorescent probe to evaluate the distribution of microtubules in normal and transformed cells grown in tissue culture. The fluorescent staining pattern of transformed and nontransformed cells is significantly different and may be used in conjunction with other morphological features to identify transformants in mixed cell populations. Normal cells are flattened, elongated, and fibroblastic; they display numerous Colcemid-sensitive fluorescent cytoplasmic filaments, presumably microtubules. Transformed cells, however, are smaller, more polygonal in shape, and contain very few cytoplasmic tubules. During mistosis the cytoplasmic microtubule complex of normal cells completely disappears, but reappears after cell division. Treatment of transformed cells with dibutyry-adenosine 3':5'-cyclic monophosphate plus testosterone or theophylline restores the normal fibroblastic appearance of the cells and stimulates the assembly of numerous cytoplasmic microtubules. This study provides further evidence for two separate microtubule entities in cycling nontransformed cells: a cytoplasmic microtubule complex and the microtubules of the mitotic spindle. Although an interchange of tubulin dimers seems to exist between microtubules in the two systems, control of tubule assembly may be under separate constraints. Stimulation of cytoplasmic microtuble assembly in transformed cells by derivatives of adenosine 3':5'-cycle monophosphate suggests that impairment of the cytoplasmic microtubule complex in these cells may be due to suboptimal levels of adenosine 3':5'-cyclic monophosphate.