Limits...
Spatial constraints dictate glial territories at murine neuromuscular junctions.

Brill MS, Lichtman JW, Thompson W, Zuo Y, Misgeld T - J. Cell Biol. (2011)

Bottom Line: Adult terminal SCs are arranged in static tile patterns, whereas young SCs dynamically intermingle.The mechanism of developmental glial segregation appears to be spatial competition, in which glial-glial and axonal-glial contacts constrain the territory of single SCs, as shown by four types of experiments: (1) laser ablation of single SCs, which led to immediate territory expansion of neighboring SCs; (2) axon removal by transection, resulting in adult SCs intermingling dynamically; (3) axotomy in mutant mice with blocked axon fragmentation in which intermingling was delayed; and (4) activity blockade, which had no immediate effects.In summary, we conclude that glial cells partition synapses by competing for perisynaptic space.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Integrated Protein Science Munich at the Institute of Neuroscience, Technische Universität München, 80802 Munich, Germany.

ABSTRACT
Schwann cells (SCs), the glial cells of the peripheral nervous system, cover synaptic terminals, allowing them to monitor and modulate neurotransmission. Disruption of glial coverage leads to axon degeneration and synapse loss. The cellular mechanisms that establish and maintain this coverage remain largely unknown. To address this, we labeled single SCs and performed time-lapse imaging experiments. Adult terminal SCs are arranged in static tile patterns, whereas young SCs dynamically intermingle. The mechanism of developmental glial segregation appears to be spatial competition, in which glial-glial and axonal-glial contacts constrain the territory of single SCs, as shown by four types of experiments: (1) laser ablation of single SCs, which led to immediate territory expansion of neighboring SCs; (2) axon removal by transection, resulting in adult SCs intermingling dynamically; (3) axotomy in mutant mice with blocked axon fragmentation in which intermingling was delayed; and (4) activity blockade, which had no immediate effects. In summary, we conclude that glial cells partition synapses by competing for perisynaptic space.

Show MeSH

Related in: MedlinePlus

Terminal SC territories are constrained by neighboring SCs at adult NMJs. (A–C) Two-photon laser–induced ablation (A) of a terminal SC (cyan; asterisk) followed by time-lapse visualization (B) of a neighboring intact terminal SC (white) of the boxed area in A. (C) Post hoc confocal analysis after BTX (red) labeling shows complete coverage of vacated territory by the remaining terminal SC. The axon (labeled by thy1-Membow; green in A) remained intact (not depicted; Video 4). (D–F) Ablation (D) of axonal SC (yellow; asterisk) and time-lapse recording (E) of terminal SC (white). Confocal analysis (F) shows expansion of terminal SC along the axon (labeled by thy1-Membow; green in D; red [BTX] in F). (F, inset) Small postsynaptic area that was vacated during expansion (higher magnification view of boxed area). (G–I). Ablation (G) of terminal SC (cyan; asterisk) and time-lapse recording (H) of adjacent axonal SC. No takeover of territory or phagocytic activity was observed, as confirmed by confocal analysis after fixation (I; axon shown in green in G, labeled by thy1-OFP3; BTX in I). The timers shown represent hours/minutes. Bars, 5 µm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC3198169&req=5

fig5: Terminal SC territories are constrained by neighboring SCs at adult NMJs. (A–C) Two-photon laser–induced ablation (A) of a terminal SC (cyan; asterisk) followed by time-lapse visualization (B) of a neighboring intact terminal SC (white) of the boxed area in A. (C) Post hoc confocal analysis after BTX (red) labeling shows complete coverage of vacated territory by the remaining terminal SC. The axon (labeled by thy1-Membow; green in A) remained intact (not depicted; Video 4). (D–F) Ablation (D) of axonal SC (yellow; asterisk) and time-lapse recording (E) of terminal SC (white). Confocal analysis (F) shows expansion of terminal SC along the axon (labeled by thy1-Membow; green in D; red [BTX] in F). (F, inset) Small postsynaptic area that was vacated during expansion (higher magnification view of boxed area). (G–I). Ablation (G) of terminal SC (cyan; asterisk) and time-lapse recording (H) of adjacent axonal SC. No takeover of territory or phagocytic activity was observed, as confirmed by confocal analysis after fixation (I; axon shown in green in G, labeled by thy1-OFP3; BTX in I). The timers shown represent hours/minutes. Bars, 5 µm.

Mentions: What determines how SCs partition NMJs at different developmental stages? Either the cellular propensity to dynamic exploration could diminish as SCs mature, or, alternatively, the dynamism of adult SCs could be suppressed by external influences. One plausible mechanism would be competition for available perisynaptic space, as SCs consolidate their territory during segregation. To test this hypothesis, we acutely ablated single SCs using a two-photon femtosecond-pulsed laser (Figs. 4 and 5 and Videos 3–6; Galbraith and Terasaki, 2003; Williams et al., 2010). By parking the high-intensity laser beam briefly inside a cell’s nucleus, we could ablate single SCs, as confirmed by ethidium homodimer (EtHD) influx (see Materials and methods; Fig. 4; Reddy et al., 2003). Targeted SCs quickly fragmented, vacating their original territory. Notably, nearby SCs that were bleached by exposure to a conventional continuous-wave laser for single-cell bleaching showed no evidence of phototoxicity (Fig. 4 and Video 3). Within minutes after the demise of the ablated cells, neighboring terminal SCs started to invade the newly vacated territory. Over the course of up to 5 h, the expanding cells engulfed the remnants of the ablated cell and covered the available space (n = 9/10 cases, six triangularis sterni explants; Figs. 4 B, 5 [A–C], and S4 and Video 4). Similarly, when the axonal SC next to an NMJ was ablated, terminal SCs swiftly overgrew the heminode to wrap the denuded axon (n = 5/5 cases, five triangularis sterni explants; Figs. 5 [D–F] and S4 and Video 5). In contrast, axonal SCs that adjoined an NMJ did not invade the synapse after ablation of terminal SCs over the same time period (n = 7/7 cases, four triangularis sterni explants; Figs. 5 [G–I] and S4 and Video 6). Hence, the lack of adult SC dynamism might be a result of spatial competition, in which neighboring cells constantly push against each other without substantial changes in synaptic area they cover. However, axonal SCs seem to be constrained by additional factors at the heminode or by their state of differentiation.


Spatial constraints dictate glial territories at murine neuromuscular junctions.

Brill MS, Lichtman JW, Thompson W, Zuo Y, Misgeld T - J. Cell Biol. (2011)

Terminal SC territories are constrained by neighboring SCs at adult NMJs. (A–C) Two-photon laser–induced ablation (A) of a terminal SC (cyan; asterisk) followed by time-lapse visualization (B) of a neighboring intact terminal SC (white) of the boxed area in A. (C) Post hoc confocal analysis after BTX (red) labeling shows complete coverage of vacated territory by the remaining terminal SC. The axon (labeled by thy1-Membow; green in A) remained intact (not depicted; Video 4). (D–F) Ablation (D) of axonal SC (yellow; asterisk) and time-lapse recording (E) of terminal SC (white). Confocal analysis (F) shows expansion of terminal SC along the axon (labeled by thy1-Membow; green in D; red [BTX] in F). (F, inset) Small postsynaptic area that was vacated during expansion (higher magnification view of boxed area). (G–I). Ablation (G) of terminal SC (cyan; asterisk) and time-lapse recording (H) of adjacent axonal SC. No takeover of territory or phagocytic activity was observed, as confirmed by confocal analysis after fixation (I; axon shown in green in G, labeled by thy1-OFP3; BTX in I). The timers shown represent hours/minutes. Bars, 5 µm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3198169&req=5

fig5: Terminal SC territories are constrained by neighboring SCs at adult NMJs. (A–C) Two-photon laser–induced ablation (A) of a terminal SC (cyan; asterisk) followed by time-lapse visualization (B) of a neighboring intact terminal SC (white) of the boxed area in A. (C) Post hoc confocal analysis after BTX (red) labeling shows complete coverage of vacated territory by the remaining terminal SC. The axon (labeled by thy1-Membow; green in A) remained intact (not depicted; Video 4). (D–F) Ablation (D) of axonal SC (yellow; asterisk) and time-lapse recording (E) of terminal SC (white). Confocal analysis (F) shows expansion of terminal SC along the axon (labeled by thy1-Membow; green in D; red [BTX] in F). (F, inset) Small postsynaptic area that was vacated during expansion (higher magnification view of boxed area). (G–I). Ablation (G) of terminal SC (cyan; asterisk) and time-lapse recording (H) of adjacent axonal SC. No takeover of territory or phagocytic activity was observed, as confirmed by confocal analysis after fixation (I; axon shown in green in G, labeled by thy1-OFP3; BTX in I). The timers shown represent hours/minutes. Bars, 5 µm.
Mentions: What determines how SCs partition NMJs at different developmental stages? Either the cellular propensity to dynamic exploration could diminish as SCs mature, or, alternatively, the dynamism of adult SCs could be suppressed by external influences. One plausible mechanism would be competition for available perisynaptic space, as SCs consolidate their territory during segregation. To test this hypothesis, we acutely ablated single SCs using a two-photon femtosecond-pulsed laser (Figs. 4 and 5 and Videos 3–6; Galbraith and Terasaki, 2003; Williams et al., 2010). By parking the high-intensity laser beam briefly inside a cell’s nucleus, we could ablate single SCs, as confirmed by ethidium homodimer (EtHD) influx (see Materials and methods; Fig. 4; Reddy et al., 2003). Targeted SCs quickly fragmented, vacating their original territory. Notably, nearby SCs that were bleached by exposure to a conventional continuous-wave laser for single-cell bleaching showed no evidence of phototoxicity (Fig. 4 and Video 3). Within minutes after the demise of the ablated cells, neighboring terminal SCs started to invade the newly vacated territory. Over the course of up to 5 h, the expanding cells engulfed the remnants of the ablated cell and covered the available space (n = 9/10 cases, six triangularis sterni explants; Figs. 4 B, 5 [A–C], and S4 and Video 4). Similarly, when the axonal SC next to an NMJ was ablated, terminal SCs swiftly overgrew the heminode to wrap the denuded axon (n = 5/5 cases, five triangularis sterni explants; Figs. 5 [D–F] and S4 and Video 5). In contrast, axonal SCs that adjoined an NMJ did not invade the synapse after ablation of terminal SCs over the same time period (n = 7/7 cases, four triangularis sterni explants; Figs. 5 [G–I] and S4 and Video 6). Hence, the lack of adult SC dynamism might be a result of spatial competition, in which neighboring cells constantly push against each other without substantial changes in synaptic area they cover. However, axonal SCs seem to be constrained by additional factors at the heminode or by their state of differentiation.

Bottom Line: Adult terminal SCs are arranged in static tile patterns, whereas young SCs dynamically intermingle.The mechanism of developmental glial segregation appears to be spatial competition, in which glial-glial and axonal-glial contacts constrain the territory of single SCs, as shown by four types of experiments: (1) laser ablation of single SCs, which led to immediate territory expansion of neighboring SCs; (2) axon removal by transection, resulting in adult SCs intermingling dynamically; (3) axotomy in mutant mice with blocked axon fragmentation in which intermingling was delayed; and (4) activity blockade, which had no immediate effects.In summary, we conclude that glial cells partition synapses by competing for perisynaptic space.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Integrated Protein Science Munich at the Institute of Neuroscience, Technische Universität München, 80802 Munich, Germany.

ABSTRACT
Schwann cells (SCs), the glial cells of the peripheral nervous system, cover synaptic terminals, allowing them to monitor and modulate neurotransmission. Disruption of glial coverage leads to axon degeneration and synapse loss. The cellular mechanisms that establish and maintain this coverage remain largely unknown. To address this, we labeled single SCs and performed time-lapse imaging experiments. Adult terminal SCs are arranged in static tile patterns, whereas young SCs dynamically intermingle. The mechanism of developmental glial segregation appears to be spatial competition, in which glial-glial and axonal-glial contacts constrain the territory of single SCs, as shown by four types of experiments: (1) laser ablation of single SCs, which led to immediate territory expansion of neighboring SCs; (2) axon removal by transection, resulting in adult SCs intermingling dynamically; (3) axotomy in mutant mice with blocked axon fragmentation in which intermingling was delayed; and (4) activity blockade, which had no immediate effects. In summary, we conclude that glial cells partition synapses by competing for perisynaptic space.

Show MeSH
Related in: MedlinePlus