Role of Myosin Va in the plasticity of the vertebrate neuromuscular junction in vivo.
BACKGROUND
Myosin Va is a motor protein involved in vesicular transport and its absence leads to movement disorders in humans (Griscelli and Elejalde syndromes) and rodents (e.g. dilute lethal phenotype in mice). We examined the role of myosin Va in the postsynaptic plasticity of the vertebrate neuromuscular junction (NMJ).


RESULTS
Dilute lethal mice showed a good correlation between the propensity for seizures, and fragmentation and size reduction of NMJs. In an aneural C2C12 myoblast cell culture, expression of a dominant-negative fragment of myosin Va led to the accumulation of punctate structures containing the NMJ marker protein, rapsyn-GFP, in perinuclear clusters. In mouse hindlimb muscle, endogenous myosin Va co-precipitated with surface-exposed or internalised acetylcholine receptors and was markedly enriched in close proximity to the NMJ upon immunofluorescence. In vivo microscopy of exogenous full length myosin Va as well as a cargo-binding fragment of myosin Va showed localisation to the NMJ in wildtype mouse muscles. Furthermore, local interference with myosin Va function in live wildtype mouse muscles led to fragmentation and size reduction of NMJs, exclusion of rapsyn-GFP from NMJs, reduced persistence of acetylcholine receptors in NMJs and an increased amount of punctate structures bearing internalised NMJ proteins.


CONCLUSIONS
In summary, our data show a crucial role of myosin Va for the plasticity of live vertebrate neuromuscular junctions and suggest its involvement in the recycling of internalised acetylcholine receptors back to the postsynaptic membrane.
Röder
Ira Verena
IV
Institute of Toxicology and Genetics, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Germany.
Petersen
Yvonne
Y
Choi
Kyeong Rok
KR
Witzemann
Veit
V
Hammer
John A
JA
Rudolf
Rüdiger
R
D000818:Animals; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024701:Myosin Type V / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000378:metabolism; D014162:Transfection
D009124:Muscle Proteins; C513082:Myo5a protein, mouse; D011978:Receptors, Nicotinic; C051609:peripheral membrane protein 43K; D049452:Green Fluorescent Proteins; D024701:Myosin Type V; D018995:Myosin Heavy Chains