cDNA that encodes active agrin

Agrin is thought to mediate the motor neuron-induced aggregation of
AChRs and AChE on the surface of muscle fibers at neuromuscular
junctions. We have isolated a cDNA from a chick brain library that,
based on sequence homology and expression experiments, codes for
active agrin. Examination of the sequence reveals considerable
similarity to homologous cDNAs previously isolated from ray and rat
libraries. A conspicuous difference is an insertion of 33 by in
chick agrin cDNA, which endows the encoded protein with AChR/AChE
aggregating activity. Homologous transcripts having the 33 by
insertion were detected in the ray CNS, which indicates that an
insertion of similar size is conserved in agrin in many, if not
all, vertebrate species. Results of in situ hybridization studies
and PCR experiments on mRNA isolated from motor neuron-enriched
fractions of the spinal cord indicate that, consistent with the
agrin hypothesis, motor neurons contain transcripts that code for
active agrin.