AGRIN-LIKE PROTEINS OF THE NEUROMUSCULAR-JUNCTION

Agrin, a molecule synthesized by motorneurons, plays a key role in the formation of the neuromuscular junction. Agrin is released; from moto neurons at the axon terminal after anterograde axonal transport and bi nds to agrin receptors present on muscle cells. Through a tyrosine kin ase-dependent signal transduction mechanism agrin induces rearrangemen t of various cytoskeletal, cytoplasmic and membrane proteins of muscle cells, giving rise to the molecular topography characteristic of post synaptic membranes. The most prominent aspect of these rearrangements is the aggregation of acetylcholine receptors and acetylcholinesterase s in postsynaptic membranes of muscle cells. Agrin and agrin-like prot eins deposited in the extracellular matrix of the synaptic cleft may a lso serve as a reservoir of trophic factors for motor neurons thereby ensuring the maintenance of a long-lasting synaptic architecture.