Neuromuscular defects in a Drosophila survival motor neuron gene mutant.
Autosomal recessive spinal muscular atrophy (SMA) is linked to mutations in the survival motor neuron (SMN) gene. The SMN protein has been implicated at several levels of mRNA biogenesis and is expressed ubiquitously. Studies in various model organisms have shown that the loss of function of the SMN gene leads to embryonic lethality. The human contains two genes encoding for SMN protein and in patients one of these is disrupted. It is thought the remaining low levels of protein produced by the second SMN gene do not suffice and result in the observed specific loss of lower motor neurons and muscle wasting. The early lethality in the animal mutants has made it difficult to understand why primarily these tissues are affected. We have isolated a Drosophila smn mutant. The fly alleles contain point mutations in smn similar to those found in SMA patients. We find that zygotic smn mutant animals show abnormal motor behavior and that smn gene activity is required in both neurons and muscle to alleviate this phenotype. Physiological experiments on the fly smn mutants show that excitatory post-synaptic currents are reduced while synaptic motor neuron boutons are disorganized, indicating defects at the neuromuscular junction. Clustering of a neurotransmitter receptor subunit in the muscle at the neuromuscular junction is severely reduced. This new Drosophila model for SMA thus proposes a functional role for SMN at the neuromuscular junction in the generation of neuromuscular defects.
Chan
Yick Bun
YB
MRC Functional Genetics Unit, Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK.
Miguel-Aliaga
Irene
I
Franks
Chris
C
Thomas
Natasha
N
Trülzsch
Barbara
B
Sattelle
David B
DB
Davies
Kay E
KE
van den Heuvel
Marcel
M
D000818:Animals; D030801:Animals, Genetically Modified; D017362:Cyclic AMP Response Element-Binding Protein; D004331:Drosophila melanogaster / Q000235:genetics*; D004594:Electrophysiology; D005260:Female; D005808:Genes, Recessive; D008297:Male; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D009134:Muscular Atrophy, Spinal / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009469:Neuromuscular Junction / Q000502:physiology*; D016601:RNA-Binding Proteins; D017470:Receptors, Glutamate / Q000378:metabolism; D055532:SMN Complex Proteins
D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D017470:Receptors, Glutamate; D055532:SMN Complex Proteins