Temporal requirement for SMN in motoneuron development

Hao, L.T., Duy, P.Q., Jontes, J.D., Wolman, M., Granato, M., and Beattie, C.E.
Human molecular genetics   22(13): 2612-25 (Journal)
Registered Authors
Beattie, Christine, Granato, Michael, Jontes, James, Wolman, Marc
MeSH Terms
  • Animals
  • Animals, Genetically Modified
  • Axons/metabolism
  • Axons/pathology
  • Disease Models, Animal
  • Motor Activity/genetics
  • Motor Neurons/metabolism*
  • Motor Neurons/pathology
  • Muscular Atrophy, Spinal/genetics
  • Muscular Atrophy, Spinal/metabolism
  • Muscular Atrophy, Spinal/mortality
  • Mutation
  • Neurogenesis/genetics*
  • Survival of Motor Neuron 1 Protein/genetics*
  • Survival of Motor Neuron 1 Protein/metabolism*
  • Zebrafish
23459934 Full text @ Hum. Mol. Genet.

Proper function of the motor unit is dependent upon the correct development of dendrites and axons. The infant/childhood onset motoneuron disease spinal muscular atrophy (SMA), caused by low levels of the survival motor neuron (SMN) protein, is characterized by muscle denervation and paralysis. Although different SMA models have shown neuromuscular junction defects and/or motor axon defects, a comprehensive analysis of motoneuron development in vivo under conditions of low SMN will give insight into why the motor unit becomes dysfunctional. We have generated genetic mutants in zebrafish expressing low levels of SMN from the earliest stages of development. Analysis of motoneurons in these mutants revealed motor axons were often shorter and had fewer branches. We also found that motoneurons had significantly fewer dendritic branches and those present were shorter. Analysis of motor axon filopodial dynamics in live embryos revealed that mutants had fewer filopodia and their average half-life was shorter. To determine when SMN was needed to rescue motoneuron development, SMN was conditionally induced in smn mutants during embryonic stages. Only when SMN was added back soon after motoneurons were born could later motor axon development be rescued. Importantly, analysis of motor behavior revealed that animals with motor axon defects had significant deficits in motor output. We also show that SMN is required earlier for motoneuron development than for survival. These data support that SMN is needed early in development for motoneuron dendrites and axons to develop normally and that this is essential for proper connectivity and movement.

Genes / Markers
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Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes