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Local ERM activation and dynamic growth cones at Schwann cell tips implicated in efficient formation of nodes of Ranvier.

Gatto CL, Walker BJ, Lambert S - J. Cell Biol. (2003)

Bottom Line: In the peripheral nervous system, axo-glial cell contacts have been implicated in Schwann cell (SC) differentiation and formation of the nodes of Ranvier.SC microvilli establish axonal contact at mature nodes, and their components have been observed to localize early to sites of developing nodes.However, a role for these contacts in node formation remains controversial.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Program in Neuroscience, University of Massachusetts Medical School, 4 Biotech, 377 Plantation St., Suite 326, Worcester, MA 01605, USA.

ABSTRACT
Nodes of Ranvier are specialized, highly polarized axonal domains crucial to the propagation of saltatory action potentials. In the peripheral nervous system, axo-glial cell contacts have been implicated in Schwann cell (SC) differentiation and formation of the nodes of Ranvier. SC microvilli establish axonal contact at mature nodes, and their components have been observed to localize early to sites of developing nodes. However, a role for these contacts in node formation remains controversial. Using a myelinating explant culture system, we have observed that SCs reorganize and polarize microvillar components, such as the ezrin-binding phosphoprotein 50 kD/regulatory cofactor of the sodium-hydrogen exchanger isoform 3 (NHERF-1), actin, and the activated ezrin, radixin, and moesin family proteins before myelination in response to inductive signals. These components are targeted to the SC distal tips where live cell imaging reveals novel, dynamic growth cone-like behavior. Furthermore, localized activation of the Rho signaling pathway at SC tips gives rise to these microvillar component-enriched "caps" and influences the efficiency of node formation.

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EBP50, actin, activated ERMs, and RhoA localize to SC tips. Isolated SCs were stained to identify other proteins residing at the tips. (A–C) EBP50 was found at the tip of α-tubulin containing SC processes. (E–G) Actin colocalized with EBP50 at the SC tip, as did activated, phospho-ERMs (I–K). Pan-ERM antibody staining revealed ERMs generally present at the SC tips. However, this staining was less concentrated at these sites than is observed with activated ERMs and more diffusely localized throughout the SC body and processes (M–O). (Q–S) In addition, the small GTPase RhoA localized generally to the SC distal tip in close proximity to EBP50. The tips examined also have corresponding magnified views of either (D, H, L, and P) phase or (T) DIC shown to detail tip morphologies. Quantitatively, 79.1 ± 1.7% (mean ± SEM) of EBP50 or phospho-ERM reactive SC tips displayed distal RhoA accumulations. Bars, 10 μm.
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fig4: EBP50, actin, activated ERMs, and RhoA localize to SC tips. Isolated SCs were stained to identify other proteins residing at the tips. (A–C) EBP50 was found at the tip of α-tubulin containing SC processes. (E–G) Actin colocalized with EBP50 at the SC tip, as did activated, phospho-ERMs (I–K). Pan-ERM antibody staining revealed ERMs generally present at the SC tips. However, this staining was less concentrated at these sites than is observed with activated ERMs and more diffusely localized throughout the SC body and processes (M–O). (Q–S) In addition, the small GTPase RhoA localized generally to the SC distal tip in close proximity to EBP50. The tips examined also have corresponding magnified views of either (D, H, L, and P) phase or (T) DIC shown to detail tip morphologies. Quantitatively, 79.1 ± 1.7% (mean ± SEM) of EBP50 or phospho-ERM reactive SC tips displayed distal RhoA accumulations. Bars, 10 μm.

Mentions: To determine whether the GFP-remodeling reflected actual changes in the morphology of the SC tip, we studied acutely dispersed SC preparations. This allowed for visualization of individual cells that was not possible without transfection in explants due to the culture complexity. As observed in explant SCs, isolated bipolar cells displayed discrete tips enriched in microvillar components, such as EBP50 and actin (Fig. 4, A–H). Furthermore, the tip-localizing ERMs were again found to be enriched in the activated versions of these proteins (Fig. 4, I–L), whereas nonphosphorylated ERMs were diffusely present in the SC body and processes (Fig. 4, M–P). Concentrations of RhoA were also observed at the SC tips (Fig. 4, Q–T). Specifically, 79.1 ± 1.7% (data presented as mean ± SEM) of SC tips that were positively immunostained for either EBP50 or phospho-ERM also displayed accumulations of RhoA.


Local ERM activation and dynamic growth cones at Schwann cell tips implicated in efficient formation of nodes of Ranvier.

Gatto CL, Walker BJ, Lambert S - J. Cell Biol. (2003)

EBP50, actin, activated ERMs, and RhoA localize to SC tips. Isolated SCs were stained to identify other proteins residing at the tips. (A–C) EBP50 was found at the tip of α-tubulin containing SC processes. (E–G) Actin colocalized with EBP50 at the SC tip, as did activated, phospho-ERMs (I–K). Pan-ERM antibody staining revealed ERMs generally present at the SC tips. However, this staining was less concentrated at these sites than is observed with activated ERMs and more diffusely localized throughout the SC body and processes (M–O). (Q–S) In addition, the small GTPase RhoA localized generally to the SC distal tip in close proximity to EBP50. The tips examined also have corresponding magnified views of either (D, H, L, and P) phase or (T) DIC shown to detail tip morphologies. Quantitatively, 79.1 ± 1.7% (mean ± SEM) of EBP50 or phospho-ERM reactive SC tips displayed distal RhoA accumulations. Bars, 10 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172691&req=5

fig4: EBP50, actin, activated ERMs, and RhoA localize to SC tips. Isolated SCs were stained to identify other proteins residing at the tips. (A–C) EBP50 was found at the tip of α-tubulin containing SC processes. (E–G) Actin colocalized with EBP50 at the SC tip, as did activated, phospho-ERMs (I–K). Pan-ERM antibody staining revealed ERMs generally present at the SC tips. However, this staining was less concentrated at these sites than is observed with activated ERMs and more diffusely localized throughout the SC body and processes (M–O). (Q–S) In addition, the small GTPase RhoA localized generally to the SC distal tip in close proximity to EBP50. The tips examined also have corresponding magnified views of either (D, H, L, and P) phase or (T) DIC shown to detail tip morphologies. Quantitatively, 79.1 ± 1.7% (mean ± SEM) of EBP50 or phospho-ERM reactive SC tips displayed distal RhoA accumulations. Bars, 10 μm.
Mentions: To determine whether the GFP-remodeling reflected actual changes in the morphology of the SC tip, we studied acutely dispersed SC preparations. This allowed for visualization of individual cells that was not possible without transfection in explants due to the culture complexity. As observed in explant SCs, isolated bipolar cells displayed discrete tips enriched in microvillar components, such as EBP50 and actin (Fig. 4, A–H). Furthermore, the tip-localizing ERMs were again found to be enriched in the activated versions of these proteins (Fig. 4, I–L), whereas nonphosphorylated ERMs were diffusely present in the SC body and processes (Fig. 4, M–P). Concentrations of RhoA were also observed at the SC tips (Fig. 4, Q–T). Specifically, 79.1 ± 1.7% (data presented as mean ± SEM) of SC tips that were positively immunostained for either EBP50 or phospho-ERM also displayed accumulations of RhoA.

Bottom Line: In the peripheral nervous system, axo-glial cell contacts have been implicated in Schwann cell (SC) differentiation and formation of the nodes of Ranvier.SC microvilli establish axonal contact at mature nodes, and their components have been observed to localize early to sites of developing nodes.However, a role for these contacts in node formation remains controversial.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Program in Neuroscience, University of Massachusetts Medical School, 4 Biotech, 377 Plantation St., Suite 326, Worcester, MA 01605, USA.

ABSTRACT
Nodes of Ranvier are specialized, highly polarized axonal domains crucial to the propagation of saltatory action potentials. In the peripheral nervous system, axo-glial cell contacts have been implicated in Schwann cell (SC) differentiation and formation of the nodes of Ranvier. SC microvilli establish axonal contact at mature nodes, and their components have been observed to localize early to sites of developing nodes. However, a role for these contacts in node formation remains controversial. Using a myelinating explant culture system, we have observed that SCs reorganize and polarize microvillar components, such as the ezrin-binding phosphoprotein 50 kD/regulatory cofactor of the sodium-hydrogen exchanger isoform 3 (NHERF-1), actin, and the activated ezrin, radixin, and moesin family proteins before myelination in response to inductive signals. These components are targeted to the SC distal tips where live cell imaging reveals novel, dynamic growth cone-like behavior. Furthermore, localized activation of the Rho signaling pathway at SC tips gives rise to these microvillar component-enriched "caps" and influences the efficiency of node formation.

Show MeSH
Related in: MedlinePlus