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Myelin & Schwann Cell Components

  Axon relations
  Other components
  Pathology: Images
  Schmidt-Lanterman cleft
  Early images
Node of Ranvier
Schwann cell
Schwann Cells: Original Description
Theodor Schwann

Myelin: Early Images

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

Neural crest cells
Schwann cell: Types
    Non-myelinating (Remak)
    Wallerian Degeneration
    Büngner bands

Schwann cells & Myelin: Domains & Structure

Molecules in selective peripheral myelin & Schwann cell regions

Myelin Glycoproteins 1

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
  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

Myelinated Axons: Regions & Major components
Region Axon Myelin or
Schwann cell
Node of
Narrow Neurofascin 186
  Na+ channels
SC Microvilli
Paranode Narrow CNTN1; Caspr1 Terminal loops
Neurofascin 155
Juxtaparanode Wide Caspr2; CNTN2
  K+ channels
Compact +

Internode Wide Necl1; Necl2 Compact
SL clefts

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)
        • Contactin 2 (CNTN2; Tag1)
      • 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
Axon Initial Segment
  • Excitatory neurons: Nav1.2 (SCN2A)
  • Inhibitory neurons: Nav1.1 (SCN1A)

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

Myelin/Oligodendrocyte Glycoprotein (MOG)

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