Cross-Reactivity of Antibody to Physarum Actin and Actins in Eukaryotic Cells Examined by Immunofluorescence

Abstract

Antibody to highly purified actin from plasmodium of Physarum polycephalum was induced in rabbits. Immunodiffusion and immunoelectrophoresis have shown that this antibody is immunologically monospecific (12). The cross-reactivity of the antibody with actins in a wide variety of eukaryotic cells and the distribution of those actins in the cells were examined by indirect immunofluorescence.
I-bands of myofibrils isolated from striated muscle of crab legs and from the mantle of squid were specifically stained by the antibody. We found that the antisera as well as normal sera contained a factor which weakly stained sea urchin sperm tails. This factor could be removed from sera by absorbing it with purified bovine brain tubulin. The acrosome of the sperm cell of a sea urchin, as well as the cytoplasmic fibers of cultured mammalian and avian cells and those of the internodal cell of Nitella, were specifically stained by the absorbed antibody. In the swarmcell of Physarum the cytoplasm was uniformly stained. Thus, the anti-Physarum actin antibody reacted with other actins in various eukaryotic cells.
Heavy meromyosin labeled with fluorescein stained the I-bands as well as the overlap regions of the A-and I-bands of myofibrils, the cytoplasmic fibers of Nitella, and the acrosome of the sperm. It also stained the tail of the aperm which was not stained with the absorbed actin antibody.