Neuromuscular

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MYELIN & SCHWANN CELL COMPONENTS

Myelin
  Axon relations
  Diseases
  Domains
  Glycoproteins
  Other components
  Pathology: Images
  Structure
    Cross-section
    Longitudinal
  Schmidt-Lanterman cleft
Node of Ranvier
Schwann cell
  Non-myelinating
    Components
  Other
  Development


Theodor Schwann

Leeuwenhoek, A. van, 1719 7

Spinal Nerve: From cow or sheep

Ranvier, L., 1872 8

Node of Ranvier: Rabbit

Ramon y Cajal 1909

Myelin Internode



Myelinated axon + Schwann cell cytoplasm Schwann Cell Development 2


Schwann cells & Myelin: Domains & Structure



Molecules in selective peripheral myelin & Schwann cell regions

Myelin Glycoproteins 1

GlycoproteinProperties
P0 Location: Compact PNS myelin; Promyelinating Schwann cells; Büngner bands
Abundant: 50% of PNS myelin proteins
Molecular: Contains sulfated N-glycans; 30-kDa
Function: Stabilizes intraperiod line of compact PNS myelin by homophilic interactions
Diseases: CMT 1B; Dejerine-Sottas (CMT III);
    Congenital Hypomyelinating neuropathy
Myelin associated glycoprotein Locations
  CNS > PNS
  Cells: Myelin-forming oligodendrocytes & Schwann cells
  Membranes: Periaxonal Schwann cell; ? Abaxonal
Molecular: 100 kDa
  N-linked glycosylation: 30% by weight; Contain sialic acid, sulfate & GlcNAc
  Binds to α2,3-linked sialic acids
Function: Axon-Glia interactions; Schmidt-Lanterman clefts
Disease: Anti-MAG neuropathy
Peripheral myelin protein-22 (PMP-22) Location: Compact PNS myelin
Molecular: 22-kDa
  Similar to PLP/DM-20 & OTM in CNS
  4 hydrophobic transmembrane domains
Forms complexes with P0 in myelin membranes Disease: CMT 1A
170 kDa glycoprotein (SAG)PNS Schwann cells & myelin
Schwann cell myelin protein (SMP)Homology to MAG
? present in humans
Myelin/Oligodendrocyte glycoprotein (MOG) Location: External surface of oligodendrocytes & CNS myelin
Oligodendrocyte-myelin glycoprotein (OMgp) Location: CNS myelin
General properties
  • Many are members of immunoglobulin superfamily
  • Often express HNK-1 carbohydrate epitope
  • Carbohydrate epitope may be involved in homophilic cell-cell interactions
  • Glycosylation
    • PNS: Major myelin proteins glycosylated
    • CNS: Major myelin proteins not glycosylated


Nodes of Ranvier & Associated Structures 6

Internode Juxtaparanode Compact myelin Compact myelin Paranode Node of Ranvier

Node of Ranvier
  • Anatomy
    • Axon
      • Smaller diameter than at internode
      • Neurofilaments closely spaced
    • Schwann cell microvilli contact axon
    • CNS: Contact is formed by perinodal astrocyte
  • Schwann cell: Microvilli
    • Membrane & Extracellular: Neurofascin (155 splice variant)
    • Intracellular: Actin; Ezrin ; Radixin ; Moesin
    • Other components
      • Gliomedin : Promotes node formation
      • Collagen V
      • Heparan sulfate proteoglycans
        • Syndecans
        • Versican (CSPG2)
  • Extracellular: Tenascin-C; Tenascin-R
  • Axon
    • Membrane
    • Sub-membrane cytoskeleton
      • AnkyrinG (ANK3) : 480 & 270 kDa splice variants
      • βIV-Spectrin (SPTBN4)
  • Images
Paranode Juxtaparanode
  • Axon
    • Anatomy: Axolemma extending 10 to 15 μM from paranode
    • Axon membrane proteins
      • Voltage gated K+ channels: Delayed rectification
      • Cell adhesion molecules
        • Contactin-associated protein-like 2 (CNTNAP2; Caspr2)
        • Tag1 (Contactin 2)
      • NCP2 (Nieman-Pick, type C2 disease)
    • Axon submembrane proteins
      • Caspr2: PDZ domain
      • Band 4.1B
      • F-Actin
      • αII/βII Spectrin
  • Schwann cell membrane
    • TAG1 (Contactin 2)
    • K+ channels
Internodal region: Components
  • Axon
    • Cell adhesion molecules
      • Necl1 (IGSF4B)
      • Necl2 (IGSF4)
  • Compact myelin
  • Schwann cell cytoplasm & membranes
    • Contains tripartite strand with components similar to juxta paranode
    • Strand apposes
      • Inner mesaxon
      • Inner region of Schmidt-Lanterman incisures
    • Molecules
      • Necl4 (IGSF4C)
      • Necl2 (IGSF4)
      • MAG
  • Basal lamina


Myelinated axon near
Paranode & Node of Ranvier


Myelin-related components, Other


Non-myelinating Schwann cells

Non-myelinating & Denervated Schwann cells: Components


Other Schwann cell components



Early growth response (EGR) genes



Myelin-Associated Glycoprotein (MAG; siglec-4) 1,4


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Return to Demyelinating neuropathies

References
1. J. Molec Neurosci 1997;7:1-12, Cell Mol Life Sci 2002;59:1851–1871, J Neurol Sci 2005;228:187-189
2. Trends Neurosci 1999;22:402-410, Journal of Peripheral Nervous System 2008;13:122–135
3. Brain 2000;123:222-233
4. Glia 2000;29:154-165
5. Neuron 2001;30:677-687
6. J Periph Nerv Sys 2002;7:1-12, Glia 2008;56:1532-1540
7. Leeuwenhoek, A. van, 1719. Epistola XXXII (p. 312)
  in Epistolae physiologicae super compluribus naturae arcanis,
  Adrianum Beman, Delft.

8. Ranvier, L., 1872. Recherches sur l’histologie et la physiologie des nerfs.
Archives de Physiologie Normale et Pathologique, 4, 129-149.


12/16/2016