A SCHWANN-CELL MATRIX COMPONENT OF NEUROMUSCULAR-JUNCTIONS AND PERIPHERAL-NERVES

Molecules localized to the synapse are potential contributors to proce sses unique to this specialized region, such as synapse formation and maintenance and synaptic transmission. We used an immunohistochemical strategy to uncover such molecules by generating antibodies that selec tively stain synaptic regions and then using the antibodies to analyse their antigens. In this study, we utilized a monoclonal antibody, mAb 6D7, to identify and characterize an antigen concentrated at frog neu romuscular junctions and in peripheral nerves. In adult muscle, immuno electron microscopy indicates that the antigen is located in the extra cellular matrix around perisynaptic Schwann cells at the neuromuscular junction and in association with myelinated and nonmyelinated axons i n peripheral nerves. The maintenance of the mAb 6D7 epitope is innerva tion-dependent but is muscle-independent; it disappears from the synap tic region within 2 weeks after denervation, but persists after muscle damage when the nerve is left intact. mAb 6D7 immunolabelling is also detected at the neuromuscular junction in developing tadpoles. Bioche mical analyses of nerve extracts indicate that mAb 6D7 recognizes a gl ycoprotein of 127 kDa with both N- and O-linked carbohydrate moieties. Taken together, the results suggest that the antigen recognized by mA b 6D7 may be a novel component of the synaptic extracellular matrix ov erlying the terminal Schwann cell. The innervation-sensitivity of the epitope at the neuromuscular junction suggests a function in the inter actions between nerves and Schwann cells.