Abstract
Agrin, a protein isolated from the synapse-rich electric organ of Torpedo californica , induces the formation of specializations on myotubes in culture which resemble the post-synaptic apparatus at the vertebrate skeletal neuromuscular junction. For example, the specializations contain aggregates of acetylcholine receptors and acetylcholinesterase. This report summarizes the evidence that the formation of the postsynaptic apparatus at developing and regenerating neuromuscular junctions is triggered by the release of agrin from motor axon terminals and describes results of recent experiments which suggest that agrininduced tyrosine phosphorylation of the β subunit of the acetylcholine receptor may play a role in receptor aggregation.