Subcellular localization and axonal transport of the survival motor neuron (SMN) protein in the developing rat spinal cord

Hum Mol Genet. 2000 Jan 1;9(1):47-56. doi: 10.1093/hmg/9.1.47.


The subcellular localization of the survival motor neuron (SMN) protein, encoded by the spinal muscular atrophy determining gene, was investigated in motor neurons of the developing and adult rat spinal cord by light and electron microscopy immunocytochemistry. The experiments were carried out with a panel of anti-SMN antibodies, all recognizing an SMN-specific protein band at 39 kDa in HeLa cells and rat spinal cord protein extracts. SMN protein expression decreased during postnatal spinal cord development, but it remained unchanged in distribution and intensity in motor neurons at all ages examined. SMN protein was mainly organized in immunoreactive aggregates sparse in the nucleoplasm and cytoplasm of both mature and developing motor neurons, and it was more rarely localized within the endoplasmic reticulum and in apposition to the external mitochondrial membrane. Most strikingly, the SMN protein was found in association with cytoskeletal elements in spinal dendrites and axons, where it was particularly evident during postnatal development. The present findings suggest that SMN protein may be transported via axoplasmic flow in maturing neurons. Given the RNA-binding activity of SMN, the SMN protein could be involved in the transport of specific mRNAs in axons and dendrites of motor neurons. The reduced transport of specific mRNAs within motor neurons during development could play a role in the motoneuronal degeneration and impaired axonal sprouting observed in spinal muscular atrophy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies / analysis
  • Axons / metabolism*
  • Axons / ultrastructure
  • Biological Transport
  • Blotting, Western
  • Cyclic AMP Response Element-Binding Protein
  • HeLa Cells / immunology
  • HeLa Cells / metabolism
  • Humans
  • Immunohistochemistry
  • Microscopy / methods
  • Microscopy, Electron
  • Motor Neurons / metabolism
  • Motor Neurons / ultrastructure
  • Nerve Tissue Proteins / immunology
  • Nerve Tissue Proteins / metabolism*
  • RNA-Binding Proteins
  • Rats
  • Rats, Sprague-Dawley
  • SMN Complex Proteins
  • Spinal Cord / growth & development*
  • Spinal Cord / metabolism*
  • Spinal Cord / ultrastructure
  • Subcellular Fractions
  • Survival of Motor Neuron 1 Protein


  • Antibodies
  • Cyclic AMP Response Element-Binding Protein
  • Nerve Tissue Proteins
  • RNA-Binding Proteins
  • SMN Complex Proteins
  • Smn1 protein, rat
  • Survival of Motor Neuron 1 Protein

Grant support