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 motoneurons at the axon terminal after anterograde axonal transport and binds to agrin receptors present on muscle cells. Through a tyrosine kinase-dependent signal transduction mechanism agrin induces rearrangement of various cytoskeletal, cytoplasmic and membrane proteins of muscle cells, giving rise to the molecular topography characteristic of postsynaptic membranes. The most prominent aspect of these rearrangements is the aggregation of acetylcholine receptors and acetylcholinesterases in postsynaptic membranes of muscle cells. Agrin and agrin-like proteins deposited in the extracellular matrix of the synaptic cleft may also serve as a reservoir of trophic factors for motor neurons thereby ensuring the maintenance of a long-lasting synaptic architecture.