Reorganization of the nuclear compartments involved in transcription and RNA processing in myonuclei of type I spinal muscular atrophy

  • María S. Castillo-Iglesias
  • María T. Berciano
  • J. Oriol Narcis
  • J. Fernando Val-Bernal
  • José C. Rodriguez-Rey
  • Olga TapiaEmail author
  • Miguel LafargaEmail author
Short Communication


Type I spinal muscular atrophy (SMA) is an autosomal recessive disorder caused by the loss or mutation of the survival motor neuron 1 (SMN1) gene. The reduction in SMN protein levels in SMA leads to the degeneration of motor neurons and muscular atrophy. In this study, we analyzed the nuclear reorganization in human skeletal myofibers from a type I SMA patient carrying a deletion of exons 7 and 8 in the SMN1 gene and two SMN2 gene copies and showing reduced SMN protein levels in the muscle compared with those in control samples. The morphometric analysis of myofiber size revealed the coexistence of atrophic and hypertrophic myofibers in SMA samples. Compared with controls, both nuclear size and the nuclear shape factor were significantly reduced in SMA myonuclei. Nuclear reorganization in SMA myonuclei was characterized by extensive heterochromatinization, the aggregation of splicing factors in large interchromatin granule clusters, and nucleolar alterations with the accumulation of the granular component and a loss of fibrillar center/dense fibrillar component units. These nuclear alterations reflect a severe perturbation of global pre-mRNA transcription and splicing, as well as nucleolar dysfunction, in SMA myofibers. Moreover, the finding of similar nuclear reorganization in both atrophic and hypetrophic myofibers provides additional support that the SMN deficiency in SMA patients may primarily affect the skeletal myofibers.


Spinal muscular atrophy SMN Skeletal myofibers Myonuclei Chromatin Perichromatin region Nuclear speckles Nucleolus 



The authors would like to thank Raquel García-Ceballos for technical assistance. This work was supported by the following grants: “Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas” (CIBERNED; CB06/05/0037) Spain, and “Instituto de Investigación Valdecilla” (IDIVAL, Next-Val), Spain.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • María S. Castillo-Iglesias
    • 1
  • María T. Berciano
    • 2
  • J. Oriol Narcis
    • 1
  • J. Fernando Val-Bernal
    • 3
  • José C. Rodriguez-Rey
    • 2
  • Olga Tapia
    • 1
    Email author
  • Miguel Lafarga
    • 1
    Email author
  1. 1.Departamento de Anatomía y Biología Celular and “Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)”Universidad de Cantabria-IDIVALSantanderSpain
  2. 2.Departamento de Biología MolecularUniversidad de Cantabria-IDIVALSantanderSpain
  3. 3.Unidad de Patología, Departamento de Ciencias Médicas y QuirúrgicasUniversidad de Cantabria-IDIVALSantanderSpain

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