Chick myotendinous antigen. I. A monoclonal antibody as a marker for tendon and muscle morphogenesis.

Abstract

Extracellular matrix components are likely to be involved in the interaction of muscle with nonmuscle cells during morphogenesis and in adult skeletal muscle. With the aim of identifying relevant molecules, monoclonal antibodies were generated that react with the endomyosium, i.e., the extracellular matrix on the surface of single muscle fibers. Antibody M1, which is described here, specifically labeled the endomysium of chick anterior latissimus dorsi muscle (but neither the perimysium nor, with the exception of blood vessels and perineurium, the epimysium). Endomysium labeling was restricted to proximal and distal portions of muscle fibers near their insertion points to tendon, but absent from medial regions of the muscle. Myotendinous junctions and tendon fascicles were intensely labeled by M1 antibody. In chick embryos, myotendinous antigen (as the epitope recognized by M1 antibody is tentatively called) appeared first in the perichondrium of vertebrae and limb cartilage elements, from where it gradually extended to the premuscle masses. Around day 6, tendon primordia were clearly labeled. The other structures labeled by M1 antibody in chick embryos were developing smooth muscle tissues, especially aorta, gizzard, and lung buds. Tissues labeled with M1 antibody appeared to be a subset of the ones accumulating fibronectin. In cell cultures, M1 antibody binds to fuzzy, fibrillar material on the substrate and cell surfaces of living fibroblast and myogenic cells, which confirms an extracellular location and its distribution in adult muscle and tendon are compatible with the idea that it might be involved in attaching muscle fibers to tendon fascicles.