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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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Dynamic EBP50/ERM-positive SC distal tips. Cultures were transfected after 1 d of induction. After 5 d of transfection, (A) EBP50-GFP was seen to colocalize with (B) endogenous phospho-ERM staining at SC tips. These transfected cultures were then examined via time-lapse microscopy. (C–F) SCs in standard cultures (d29/t7) showed no specific localization of EBP50-GFP at their tips (arrows). (G–J) SC in myelinating cultures (d29/M6/t5) had dynamic, remodeling EBP50-GFP–positive tips (arrowheads). (K–O) Furthermore, deconvolution microscopy revealed EBP50-GFP as having a punctate distribution. Bars, 10 μm.
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fig3: Dynamic EBP50/ERM-positive SC distal tips. Cultures were transfected after 1 d of induction. After 5 d of transfection, (A) EBP50-GFP was seen to colocalize with (B) endogenous phospho-ERM staining at SC tips. These transfected cultures were then examined via time-lapse microscopy. (C–F) SCs in standard cultures (d29/t7) showed no specific localization of EBP50-GFP at their tips (arrows). (G–J) SC in myelinating cultures (d29/M6/t5) had dynamic, remodeling EBP50-GFP–positive tips (arrowheads). (K–O) Furthermore, deconvolution microscopy revealed EBP50-GFP as having a punctate distribution. Bars, 10 μm.

Mentions: To visualize the dynamics of cap formation in live cells, an EBP50-GFP fusion construct was used. When transfected into myelinating DRG cultures, this construct was observed to localize to cap structures at SC tips (Fig. 3 A). Moreover, this localization required the ERM binding site of EBP50 (unpublished data). As the binding site for EBP50 is masked on inactive ERM molecules (Gary and Bretscher, 1995; Matsui et al., 1998), these results suggest that localization of EBP50-GFP to SC caps reflects the local activation of ERM molecules at these sites. In support of this idea, EBP50-GFP was found to colocalize with COOH-terminal phospho-ERM staining (Fig. 3 B), indicative of active forms of these proteins (Reczek et al., 1997; Reczek and Bretscher, 1998).


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)

Dynamic EBP50/ERM-positive SC distal tips. Cultures were transfected after 1 d of induction. After 5 d of transfection, (A) EBP50-GFP was seen to colocalize with (B) endogenous phospho-ERM staining at SC tips. These transfected cultures were then examined via time-lapse microscopy. (C–F) SCs in standard cultures (d29/t7) showed no specific localization of EBP50-GFP at their tips (arrows). (G–J) SC in myelinating cultures (d29/M6/t5) had dynamic, remodeling EBP50-GFP–positive tips (arrowheads). (K–O) Furthermore, deconvolution microscopy revealed EBP50-GFP as having a punctate distribution. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172691&req=5

fig3: Dynamic EBP50/ERM-positive SC distal tips. Cultures were transfected after 1 d of induction. After 5 d of transfection, (A) EBP50-GFP was seen to colocalize with (B) endogenous phospho-ERM staining at SC tips. These transfected cultures were then examined via time-lapse microscopy. (C–F) SCs in standard cultures (d29/t7) showed no specific localization of EBP50-GFP at their tips (arrows). (G–J) SC in myelinating cultures (d29/M6/t5) had dynamic, remodeling EBP50-GFP–positive tips (arrowheads). (K–O) Furthermore, deconvolution microscopy revealed EBP50-GFP as having a punctate distribution. Bars, 10 μm.
Mentions: To visualize the dynamics of cap formation in live cells, an EBP50-GFP fusion construct was used. When transfected into myelinating DRG cultures, this construct was observed to localize to cap structures at SC tips (Fig. 3 A). Moreover, this localization required the ERM binding site of EBP50 (unpublished data). As the binding site for EBP50 is masked on inactive ERM molecules (Gary and Bretscher, 1995; Matsui et al., 1998), these results suggest that localization of EBP50-GFP to SC caps reflects the local activation of ERM molecules at these sites. In support of this idea, EBP50-GFP was found to colocalize with COOH-terminal phospho-ERM staining (Fig. 3 B), indicative of active forms of these proteins (Reczek et al., 1997; Reczek and Bretscher, 1998).

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