Isolation and characterization of a cDNA that encodes an agrin homolog in the marine ray

Agrin, the protein thought to trigger motor neuron-induced aggregation of postsynaptic molecules at the developing neuromuscular junction, has been purified from the synapse-rich electric organ of the marine ray. In order to study agrin's role in synaptogenesis and to examine its relationship to antigenically similar proteins, we isolated from a marine ray library a partial cDNA, OL4, which codes for a member of the agrin protein family. Sequence analysis shows that agrin and agrin-related proteins contain regions similar to basal lamina proteins and other secreted molecules including laminin, epidermal growth factor, and pancreatic secretory trypsin inhibitors. Northern blot analysis revealed transcripts in several different tissues, but the highest levels of expression are in brain and spinal cord. In situ hybridization studies demonstrate that agrin/agrin-related mRNAs are present in motor neurons that innervate the electric organ and skeletal muscle. They also reveal that agrin/agrin-related transcripts have a broad distribution in neurons and nonneural cells in the CNS, raising the possibility that agrin and/or agrin-related proteins mediate formation of the postsynaptic apparatus at neuron-to-neuron synapses.