ANTIBODY TO THYMUS MYOSIN - ITS IMMUNOLOGICAL CHARACTERIZATION AND USE FOR IMMUNOCYTOCHEMICAL LOCALIZATION OF MYOSIN IN VERTEBRATE NON-MUSCLE CELLS

Abstract

Thymus myosin differs immunologically from smooth muscle and striated muscle myosin isoenzymes. In the enzyme-linked immunosorbent assay a moderate degree of cross reaction was observed between anti-calf-thymus myosin and myosin from chicken gizzard (.apprx. 50% of the titer of the homologous reaction). In contrast, the cross reactivity between thymus myosin and antibodies to gizzard myosin was very low (.apprx. 5%) and no significant cross reaction was observed between thymus myosin and antibodies to striated muscle myosin and vice versa (below 1%). Antibodies to thymus myosin were further distinguished from antibodies to gizzard and striated muscle myosin by their reaction with both smooth muscle and a very broad spectrum of vertebrate [rat, calf, frog] nonmuscle cells. Nonmuscle cells reacting with anti-thymus myosin included cell types which did not display any detectable affinity for antigizzard myosin (e.g. lymphocytes, polymorphonuclear leukocytes, vascular endothelium, adrenal chromaffin cells) and cell types which reacted with anti-gizzard myosin as well (e.g., intestinal epithelial brush border, thymic epithelial cells, liver cells and stress fibers of cultured cells). Anti-thymus myosin is a potent tool for investigating the intracellular localization of myosin in most if not all vertebrate nonmuscle cells. With respect to lymphatic tissue the present findings indicate that lymphocyte maturation appears to be accompanied by an increased level of expression of myosin and filamentous actin (the latter was visualized by labeled phalloidin). On the ultrastructural level, gold labeled antibodies to thymus myosin bound preferentially to the head region of in vitro assembled thymus myosin filaments. In cultured cells ([rat kangaroo kidney] PtK1) the antibodies showed a particular affinity for stress fiber densities, and in lymphocytes the anti-myosin label (immunoperoxidase) displayed a more or less diffuse distribution which was similar to the distribution of actin filaments (identified by decoration with heavy meromyosin).