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

Abstract

Antibody to highly purified actin from plasmodium of P. polycephalum was induced in rabbits. This antibody is immunologically monospecific. The cross-reactivity of the antibody with actins in a 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. The antisera and normal sera contained a factor which weakly stained sea urchin sperm tails. This factor was removed from sera by absorbing it with purified bovine brain tubulin. The acrosome of the sperm cell of a sea urchin and the cytoplasmic fibers of cultured mammalian [mouse ascites tumor cells, human oral epidermoid carcinoma KB cells, rat kangaroo Pt-Kl cells, mouse melanoma B-16 cells] and avian [chick fibroblasts, chick lens epithelial] 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. The anti-Physarum actin antibody reacted with other actins in various eukaryotic cells. Heavy meromyosin labeled with fluorescein stained the I-bands and 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 sperm which was not stained with the absorbed actin antibody.