Nuclear immunofluorescence by a monoclonal antibody against microtubule-associated protein-1 as it is associated with cell proliferation and transformation

Monoclonal antibody against microtubule-associated protein-1 produced intranuclear immunofluorescent spots, which disappeared under growth-inhibited conditions caused by serum starvation and saturated cell density in untransformed cells. A change of medium to 10% serum gave rise to the reappearance of nuclear spots before the resumption of DNA synthesis. This reversible change of immunofluorescence was also caused by a temperature shift in rat 3Y1 cells transformed by Simian virus-40-A640 (temperature-sensitive in large T-antigen). The fluorescence decreased during S phase of the cell cycle. In contrast the transformed cells always showed nuclear fluorescence, irrespective of serum concentrations or the cell cycle. Growth-inhibited cells previously treated with detergent and salt revealed nuclear fluorescent spots. This result suggested antigenic modification.