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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 diffusion results in labeling of adaxonal and abaxonal cytoplasm. Shown are images taken after pressure injection  (40 psi, 250-ms pulses, 2 Hz for 1–3 minutes) of 5,6-carboxyfluorescein into a myelinating Schwann cell. (A) Schwann cell perinuclear region and incisures visualized with polarized light. (B) After injection, the fiber was immunostained for MAG, which is  localized to incisures and colocalizes with incisures identified  with polarized light. (C) Image taken about midway through  depth of the cell shows that dye occupies the outer and inner collar of Schwann cell cytoplasm, creating a double train track pattern indicative of the radial diffusion of dye through incisures.  Bracket, region enlarged in E. (D) Image taken at ∼5 μm above  the plane shown in G reveals fingers of cytoplasm on the surface  of the cell; these are easily distinguished from the double train  track pattern. (E) Enlargement of region indicated by brackets in  C; arrowheads indicate position of the line across which intensity  was mapped. (F) Histogram of intensity across line perpendicular  to the long axis of the fiber at location indicated by arrowhead;  scale is the same as in image shown in E. Doublet of peaks on either end of the histogram is the quantitative representation of the  double train track pattern evident in the image shown in E. Vertical scale is 0–255 intensity levels. Bars, 10 μm.
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Figure 2: Dye diffusion results in labeling of adaxonal and abaxonal cytoplasm. Shown are images taken after pressure injection (40 psi, 250-ms pulses, 2 Hz for 1–3 minutes) of 5,6-carboxyfluorescein into a myelinating Schwann cell. (A) Schwann cell perinuclear region and incisures visualized with polarized light. (B) After injection, the fiber was immunostained for MAG, which is localized to incisures and colocalizes with incisures identified with polarized light. (C) Image taken about midway through depth of the cell shows that dye occupies the outer and inner collar of Schwann cell cytoplasm, creating a double train track pattern indicative of the radial diffusion of dye through incisures. Bracket, region enlarged in E. (D) Image taken at ∼5 μm above the plane shown in G reveals fingers of cytoplasm on the surface of the cell; these are easily distinguished from the double train track pattern. (E) Enlargement of region indicated by brackets in C; arrowheads indicate position of the line across which intensity was mapped. (F) Histogram of intensity across line perpendicular to the long axis of the fiber at location indicated by arrowhead; scale is the same as in image shown in E. Doublet of peaks on either end of the histogram is the quantitative representation of the double train track pattern evident in the image shown in E. Vertical scale is 0–255 intensity levels. Bars, 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)

Dye diffusion results in labeling of adaxonal and abaxonal cytoplasm. Shown are images taken after pressure injection  (40 psi, 250-ms pulses, 2 Hz for 1–3 minutes) of 5,6-carboxyfluorescein into a myelinating Schwann cell. (A) Schwann cell perinuclear region and incisures visualized with polarized light. (B) After injection, the fiber was immunostained for MAG, which is  localized to incisures and colocalizes with incisures identified  with polarized light. (C) Image taken about midway through  depth of the cell shows that dye occupies the outer and inner collar of Schwann cell cytoplasm, creating a double train track pattern indicative of the radial diffusion of dye through incisures.  Bracket, region enlarged in E. (D) Image taken at ∼5 μm above  the plane shown in G reveals fingers of cytoplasm on the surface  of the cell; these are easily distinguished from the double train  track pattern. (E) Enlargement of region indicated by brackets in  C; arrowheads indicate position of the line across which intensity  was mapped. (F) Histogram of intensity across line perpendicular  to the long axis of the fiber at location indicated by arrowhead;  scale is the same as in image shown in E. Doublet of peaks on either end of the histogram is the quantitative representation of the  double train track pattern evident in the image shown in E. Vertical scale is 0–255 intensity levels. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Dye diffusion results in labeling of adaxonal and abaxonal cytoplasm. Shown are images taken after pressure injection (40 psi, 250-ms pulses, 2 Hz for 1–3 minutes) of 5,6-carboxyfluorescein into a myelinating Schwann cell. (A) Schwann cell perinuclear region and incisures visualized with polarized light. (B) After injection, the fiber was immunostained for MAG, which is localized to incisures and colocalizes with incisures identified with polarized light. (C) Image taken about midway through depth of the cell shows that dye occupies the outer and inner collar of Schwann cell cytoplasm, creating a double train track pattern indicative of the radial diffusion of dye through incisures. Bracket, region enlarged in E. (D) Image taken at ∼5 μm above the plane shown in G reveals fingers of cytoplasm on the surface of the cell; these are easily distinguished from the double train track pattern. (E) Enlargement of region indicated by brackets in C; arrowheads indicate position of the line across which intensity was mapped. (F) Histogram of intensity across line perpendicular to the long axis of the fiber at location indicated by arrowhead; scale is the same as in image shown in E. Doublet of peaks on either end of the histogram is the quantitative representation of the double train track pattern evident in the image shown in E. Vertical scale is 0–255 intensity levels. Bars, 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
Related in: MedlinePlus