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Functional gap junctions in the schwann cell myelin sheath.

Balice-Gordon RJ, Bone LJ, Scherer SS - J. Cell Biol. (1998)

Bottom Line: Gap junctions are localized to periodic interruptions in the compact myelin called Schmidt-Lanterman incisures and to paranodes; these regions contain at least one gap junction protein, connexin32 (Cx32).The radial diffusion of low molecular weight dyes across the myelin sheath was not interrupted in myelinating Schwann cells from cx32- mice, indicating that other connexins participate in forming gap junctions in these cells.Owing to the unique geometry of myelinating Schwann cells, a gap junction-mediated radial pathway may be essential for rapid diffusion between the adaxonal and perinuclear cytoplasm, since this radial pathway is approximately one million times faster than the circumferential pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA. rbaliceg@mail.med.upenn.edu

ABSTRACT
The Schwann cell myelin sheath is a multilamellar structure with distinct structural domains in which different proteins are localized. Intracellular dye injection and video microscopy were used to show that functional gap junctions are present within the myelin sheath that allow small molecules to diffuse between the adaxonal and perinuclear Schwann cell cytoplasm. Gap junctions are localized to periodic interruptions in the compact myelin called Schmidt-Lanterman incisures and to paranodes; these regions contain at least one gap junction protein, connexin32 (Cx32). The radial diffusion of low molecular weight dyes across the myelin sheath was not interrupted in myelinating Schwann cells from cx32- mice, indicating that other connexins participate in forming gap junctions in these cells. Owing to the unique geometry of myelinating Schwann cells, a gap junction-mediated radial pathway may be essential for rapid diffusion between the adaxonal and perinuclear cytoplasm, since this radial pathway is approximately one million times faster than the circumferential pathway.

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Cx32 and E-cadherin immunoreactivity in  paranodes and incisures.  Teased fibers from an adult  rat sciatic nerve fixed for 30  min in Zamboni's fixative  were immunostained with a  monoclonal antibody against  Cx32 (A; fluorescein optics)  and a rabbit antiserum against  E-cadherin (B; rhodamine  optics). Cx32 and E-cadherin  colocalize at paranodes, which  flank nodes of Ranvier (apposed arrowheads), as well as  incisures, some of which are  marked (arrows). E-cadherin  also stains mesaxons, one of  which is seen in this focal  plane (open arrow). Note that  although E-cadherin and Cx32  immunoreactivity colocalize,  E-cadherin staining is more  pronounced at incisures,  whereas Cx32 staining is more  pronounced at paranodes. In  addition, the subcellular distributions of E-cadherin and  Cx32 immunoreactivity within  paranodes appear to differ.  Bar, 10 μm.
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Figure 3: Cx32 and E-cadherin immunoreactivity in paranodes and incisures. Teased fibers from an adult rat sciatic nerve fixed for 30 min in Zamboni's fixative were immunostained with a monoclonal antibody against Cx32 (A; fluorescein optics) and a rabbit antiserum against E-cadherin (B; rhodamine optics). Cx32 and E-cadherin colocalize at paranodes, which flank nodes of Ranvier (apposed arrowheads), as well as incisures, some of which are marked (arrows). E-cadherin also stains mesaxons, one of which is seen in this focal plane (open arrow). Note that although E-cadherin and Cx32 immunoreactivity colocalize, E-cadherin staining is more pronounced at incisures, whereas Cx32 staining is more pronounced at paranodes. In addition, the subcellular distributions of E-cadherin and Cx32 immunoreactivity within paranodes appear to differ. Bar, 10 μm.

Mentions: Teased fibers were viewed with polarized light, revealing the locations of incisures, which are funnel-shaped, isotropic structures that interrupt the anisotropic compact myelin (Fig. 2 A). In some fibers, we directly demonstrated that these isotropic structures are incisures by fixing the fibers and immunostaining them for MAG, which is localized to incisures and the adaxonal surface of myelinating Schwann cells (Fig. 2 B). Finally, we double labeled teased fibers with antibodies against Cx32 and E-cadherin, which were colocalized at incisures and paranodes (Fig. 3). Thus, incisures can visualize in living teased fibers, and contain Cx32, MAG, and E-cadherin.


Functional gap junctions in the schwann cell myelin sheath.

Balice-Gordon RJ, Bone LJ, Scherer SS - J. Cell Biol. (1998)

Cx32 and E-cadherin immunoreactivity in  paranodes and incisures.  Teased fibers from an adult  rat sciatic nerve fixed for 30  min in Zamboni's fixative  were immunostained with a  monoclonal antibody against  Cx32 (A; fluorescein optics)  and a rabbit antiserum against  E-cadherin (B; rhodamine  optics). Cx32 and E-cadherin  colocalize at paranodes, which  flank nodes of Ranvier (apposed arrowheads), as well as  incisures, some of which are  marked (arrows). E-cadherin  also stains mesaxons, one of  which is seen in this focal  plane (open arrow). Note that  although E-cadherin and Cx32  immunoreactivity colocalize,  E-cadherin staining is more  pronounced at incisures,  whereas Cx32 staining is more  pronounced at paranodes. In  addition, the subcellular distributions of E-cadherin and  Cx32 immunoreactivity within  paranodes appear to differ.  Bar, 10 μm.
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Related In: Results  -  Collection

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Figure 3: Cx32 and E-cadherin immunoreactivity in paranodes and incisures. Teased fibers from an adult rat sciatic nerve fixed for 30 min in Zamboni's fixative were immunostained with a monoclonal antibody against Cx32 (A; fluorescein optics) and a rabbit antiserum against E-cadherin (B; rhodamine optics). Cx32 and E-cadherin colocalize at paranodes, which flank nodes of Ranvier (apposed arrowheads), as well as incisures, some of which are marked (arrows). E-cadherin also stains mesaxons, one of which is seen in this focal plane (open arrow). Note that although E-cadherin and Cx32 immunoreactivity colocalize, E-cadherin staining is more pronounced at incisures, whereas Cx32 staining is more pronounced at paranodes. In addition, the subcellular distributions of E-cadherin and Cx32 immunoreactivity within paranodes appear to differ. Bar, 10 μm.
Mentions: Teased fibers were viewed with polarized light, revealing the locations of incisures, which are funnel-shaped, isotropic structures that interrupt the anisotropic compact myelin (Fig. 2 A). In some fibers, we directly demonstrated that these isotropic structures are incisures by fixing the fibers and immunostaining them for MAG, which is localized to incisures and the adaxonal surface of myelinating Schwann cells (Fig. 2 B). Finally, we double labeled teased fibers with antibodies against Cx32 and E-cadherin, which were colocalized at incisures and paranodes (Fig. 3). Thus, incisures can visualize in living teased fibers, and contain Cx32, MAG, and E-cadherin.

Bottom Line: Gap junctions are localized to periodic interruptions in the compact myelin called Schmidt-Lanterman incisures and to paranodes; these regions contain at least one gap junction protein, connexin32 (Cx32).The radial diffusion of low molecular weight dyes across the myelin sheath was not interrupted in myelinating Schwann cells from cx32- mice, indicating that other connexins participate in forming gap junctions in these cells.Owing to the unique geometry of myelinating Schwann cells, a gap junction-mediated radial pathway may be essential for rapid diffusion between the adaxonal and perinuclear cytoplasm, since this radial pathway is approximately one million times faster than the circumferential pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA. rbaliceg@mail.med.upenn.edu

ABSTRACT
The Schwann cell myelin sheath is a multilamellar structure with distinct structural domains in which different proteins are localized. Intracellular dye injection and video microscopy were used to show that functional gap junctions are present within the myelin sheath that allow small molecules to diffuse between the adaxonal and perinuclear Schwann cell cytoplasm. Gap junctions are localized to periodic interruptions in the compact myelin called Schmidt-Lanterman incisures and to paranodes; these regions contain at least one gap junction protein, connexin32 (Cx32). The radial diffusion of low molecular weight dyes across the myelin sheath was not interrupted in myelinating Schwann cells from cx32- mice, indicating that other connexins participate in forming gap junctions in these cells. Owing to the unique geometry of myelinating Schwann cells, a gap junction-mediated radial pathway may be essential for rapid diffusion between the adaxonal and perinuclear cytoplasm, since this radial pathway is approximately one million times faster than the circumferential pathway.

Show MeSH