SIGNALING MECHANISMS MEDIATING SYNAPSE FORMATION

Recent experiments have begun to decipher the molecular dialog that me diates differentiation at sites of synaptic contact between neurons an d their targets. It had been hypothesized that the protein agrin is re leased by axon terminals at embryonic neuromuscular junctions and bind s to a receptor on the myofiber surface to trigger postsynaptic differ entiation. Now a genetic 'knockout' experiment has confirmed the essen tial role of agrin in signaling between developing nerve and muscle((1 )). A second 'knockout' has shown that the muscle-specific receptor ty rosine kinase MuSK is a critical element in the agrin-induced signalin g cascade((2)). Additional results suggest that MuSK may comprise a po rtion of the agrin receptor((3)).