Disruption of the mouse Large gene in the enr and myd mutants results in nerve, muscle, and neuromuscular junction defects

The autosomal recessive neuromuscular disorder associated with the enervated (enr) mouse transgene insertion manifests impaired peripheral nerve regeneration due to defects in Schwann cells and resembles the myodystrophy (Large^myd) phenotype. Here we show that the enr transgene has integrated into Chr 8 approximately 160 kb downstream from the 3′ end of the Large gene disrupting its expression as confirmed by the lack of genetic complementation between Large^myd and enr mice, the very low Large mRNA levels in enr tissues and hypoglycosylation of α-dystroglycan, a known substrate of LARGE. Mutant nerve conduction and grip strength were impaired whereas sodium channel clustering at the nodes of Ranvier was unaffected. Interestingly, the mutant neuromuscular junctions displayed abnormal acetylcholine receptor clustering with reduced immunostaining for β-dystroglycan, laminin, agrin, MuSK, and to a lesser extent acetylcholinesterase and rapsyn. These data implicate LARGE in nerve, muscle, and neuromuscular junction function.