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A more recent version of this article appeared on August 1, 2007
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Submitted on February 2, 2007
Revised on April 9, 2007
Accepted on May 17, 2007
Department of Molecular, Cellular, and Developmental Biology and Neuroscience Program, University of Michigan, Ann Arbor, MI 48109
Monitoring Editor: Tom U. Martin
Acetylcholinesterase (AChE) is an enzyme that terminates acetylcholine neurotransmitter function at the synaptic cleft of cholinergic synapses. However, the mechanism by which AChE number and density are maintained at the synaptic cleft is poorly understood. In this work, we used fluorescence recovery after photo-bleaching (FRAP), photo-unbinding and quantitative fluorescence imaging to investigate the surface mobility and stability of AChE at the adult innervated neuromuscular junction (NMJ) of living mice. In wild type synapses, we found that nonsynaptic (peri-synaptic and extra-synaptic) AChEs are mobile and gradually recruited into synaptic sites and that most of the trapped AChEs come from the peri-junctional pool. Selective labeling of a subset of synaptic AChEs within the synapse using sequential unbinding and relabeling with different colors of streptavidin followed by time lapse imaging showed that synaptic AChEs are nearly immobile. At neuromuscular junctions of mice deficient in alpha dystrobrevin, a component of the dystrophin glycoprotein complex, we found that the density and distribution of synaptic AChEs are profoundly altered and the loss rate of AChE significantly increased. These results demonstrate that nonsynaptic AChEs are mobile while synaptic AChEs are more stable, and that alpha-dystrobrevin is important for controlling the density and stability of AChEs at neuromuscular synapses.