CEREBELLAR GRANULE CELLS EXPRESS A SPECIFIC ISOFORM OF AGRIN THAT LACKS THE ACETYLCHOLINE-RECEPTOR AGGREGATING ACTIVITY

Again is a synapse-organizing molecule that mediates nerve-induced agg regation of acetylcholine receptors and other postsynaptic components at the developing acid regenerating vertebrate neuromuscular junctions . Several lines of evidence indicate that agrin might play re similar role in directing the organization of postsynaptic specifications of n euron-neuron synapse formation. Here we used immunological methods and polymerase chain reaction to identify the expression of agrin protein and alternatively spliced mRNA isoforms in the culture of rat granule cells. Anti-agrin polyclonal antibody labeled the cultured granule ce lls and it detected a protein of over 200 kDa in size from the lysate of the cultured cells, Analysis by polymerase chain reaction showed th at the granule cells in culture expressed predominantly the B-0 isofor m of agrin mRNA. When granule cells were co-cultured with primary chic k myotubes, there was no detectable effect on the aggregation of acety lcholine receptors on the surface of the myotubes, These results show that the cerebellar granule cells, similar to motor neurons in vitro, express and secrete agrin but it lacks the acetylcholine receptor aggr egating activity.