MUSCLE AGRIN - NEURAL REGULATION AND LOCALIZATION AT NERVE-INDUCED ACETYLCHOLINE-RECEPTOR CLUSTERS

The synapse-organizing protein agrin is expressed by muscle cells. In this study we begin to characterize the role of muscle agrin in synaps e formation by investigating its distribution and expression during th e formation of nerve-induced ACh receptor (AChR) aggregates in vitro. We have used species-specific anti-agrin antibodies to show that muscl e agrin colocalizes with nerve-induced AChR clusters in chimeric nerve -muscle cocultures. Furthermore, quantitation by radioimmune assay sho ws that the expression of muscle agrin by cultured chick myotubes is i ncreased more than twofold by coculture with cells from the motoneuron -rich ventral spinal cord. These data suggest a role for muscle agrin in neuromuscular junction development.