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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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Dye injection into living, teased myelinated fibers from mouse sciatic nerve. Shown are  images of a single fiber that was iontophoretically injected with 5,6-carboxyfluorescein. (A)  Polarized light in combination with fluorescent  bis-benzamide staining (inset) shows an electrode near a Schwann cell nucleus. (B) Diffusion  of 5,6-carboxyfluorescein during iontophoretic  injection. (C) Diffusion of dye from node to  node was observed within 0.5–5 min (this image  was captured at ∼1 min into injection). (D) After imaging of dye diffusion, injected fibers were  mapped at lower magnification relative to grid  lines (same field as C) to facilitate identification  for confocal microscopic analysis. Bars, 10 μm.
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Figure 1: Dye injection into living, teased myelinated fibers from mouse sciatic nerve. Shown are images of a single fiber that was iontophoretically injected with 5,6-carboxyfluorescein. (A) Polarized light in combination with fluorescent bis-benzamide staining (inset) shows an electrode near a Schwann cell nucleus. (B) Diffusion of 5,6-carboxyfluorescein during iontophoretic injection. (C) Diffusion of dye from node to node was observed within 0.5–5 min (this image was captured at ∼1 min into injection). (D) After imaging of dye diffusion, injected fibers were mapped at lower magnification relative to grid lines (same field as C) to facilitate identification for confocal microscopic analysis. Bars, 10 μm.

Mentions: Injected neurobiotin was visualized after fixation in 4% paraformaldehyde and permeabilization with acid alcohol. Fibers were blocked in 5% fish skin gelatin and 0.1% Triton X-100, labeled with 50 μg/ml rhodamine-conjugated strepavidin (Sigma Chemical Co.). Injected Schwann cells were then relocated using the etched grid as a guide (see Fig. 1, C and D) and imaged using confocal microscopy.


Functional gap junctions in the schwann cell myelin sheath.

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

Dye injection into living, teased myelinated fibers from mouse sciatic nerve. Shown are  images of a single fiber that was iontophoretically injected with 5,6-carboxyfluorescein. (A)  Polarized light in combination with fluorescent  bis-benzamide staining (inset) shows an electrode near a Schwann cell nucleus. (B) Diffusion  of 5,6-carboxyfluorescein during iontophoretic  injection. (C) Diffusion of dye from node to  node was observed within 0.5–5 min (this image  was captured at ∼1 min into injection). (D) After imaging of dye diffusion, injected fibers were  mapped at lower magnification relative to grid  lines (same field as C) to facilitate identification  for confocal microscopic analysis. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132877&req=5

Figure 1: Dye injection into living, teased myelinated fibers from mouse sciatic nerve. Shown are images of a single fiber that was iontophoretically injected with 5,6-carboxyfluorescein. (A) Polarized light in combination with fluorescent bis-benzamide staining (inset) shows an electrode near a Schwann cell nucleus. (B) Diffusion of 5,6-carboxyfluorescein during iontophoretic injection. (C) Diffusion of dye from node to node was observed within 0.5–5 min (this image was captured at ∼1 min into injection). (D) After imaging of dye diffusion, injected fibers were mapped at lower magnification relative to grid lines (same field as C) to facilitate identification for confocal microscopic analysis. Bars, 10 μm.
Mentions: Injected neurobiotin was visualized after fixation in 4% paraformaldehyde and permeabilization with acid alcohol. Fibers were blocked in 5% fish skin gelatin and 0.1% Triton X-100, labeled with 50 μg/ml rhodamine-conjugated strepavidin (Sigma Chemical Co.). Injected Schwann cells were then relocated using the etched grid as a guide (see Fig. 1, C and D) and imaged using confocal microscopy.

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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