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

Acute axon removal causes delayed SC expansion. (A) NMJ with single-cell labeling before two-photon laser–induced axonal degeneration (SCs pseudocolored in white, magenta, and yellow). The axon was severed at the second node of Ranvier away from the synapse (white arrow indicating direction; not in frame). (B) Time-lapse recording over a period of 5 h shows AAD (note fragmentation after 1 h), which led to local SC outgrowth (orange arrowheads; shown in area boxed in A). (C and D) Fixation after 5 h and staining for BTX reveal local outgrowth along several NMJ branches (orange arrowheads in D show fixed SC channel only in the area boxed in C). 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

fig7: Acute axon removal causes delayed SC expansion. (A) NMJ with single-cell labeling before two-photon laser–induced axonal degeneration (SCs pseudocolored in white, magenta, and yellow). The axon was severed at the second node of Ranvier away from the synapse (white arrow indicating direction; not in frame). (B) Time-lapse recording over a period of 5 h shows AAD (note fragmentation after 1 h), which led to local SC outgrowth (orange arrowheads; shown in area boxed in A). (C and D) Fixation after 5 h and staining for BTX reveal local outgrowth along several NMJ branches (orange arrowheads in D show fixed SC channel only in the area boxed in C). The timers shown represent hours/minutes. Bars, 5 µm.

Mentions: Hence, not only neighboring SCs but also the underlying axon might suppress SC intermingling at mature NMJs. However, as Wallerian degeneration sets in with a delay, the evidence is less direct than in the case of acute laser ablation of a neighboring SC. Therefore, we sought to acutely remove axon terminals by inducing acute axonal degeneration (AAD), which fragments axon segments around a transection site within 30 min (Kerschensteiner et al., 2005). We transected single motor axons one node of Ranvier proximal of the final heminode using a two-photon laser (see Materials and methods; Galbraith and Terasaki, 2003; Turney and Lichtman, 2008). We then labeled single terminal SCs by sequential bleaching. As soon as fragmentation set in, terminal SCs appeared to engulf the resulting axonal debris. Soon after this (<4–5 h after laser axotomy), we observed the first outgrowth of small filopodial-like SC processes that invaded the neighboring territory (Fig. 7). Although this response appeared less dramatic than the response seen after SC ablation, careful inspection of image stacks of laser-axotomized NMJs still revealed fast volume expansion of SCs. As expected from the removal of axon terminals, which underlie all synaptic SCs, this expansion mostly occurred in the z direction along the optical axis of observation (unpublished data). Collectively, these data suggest that after axon removal, terminal SCs first expand into the vacated gutter and then start sending out processes to explore surrounding territory.


Spatial constraints dictate glial territories at murine neuromuscular junctions.

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

Acute axon removal causes delayed SC expansion. (A) NMJ with single-cell labeling before two-photon laser–induced axonal degeneration (SCs pseudocolored in white, magenta, and yellow). The axon was severed at the second node of Ranvier away from the synapse (white arrow indicating direction; not in frame). (B) Time-lapse recording over a period of 5 h shows AAD (note fragmentation after 1 h), which led to local SC outgrowth (orange arrowheads; shown in area boxed in A). (C and D) Fixation after 5 h and staining for BTX reveal local outgrowth along several NMJ branches (orange arrowheads in D show fixed SC channel only in the area boxed in C). 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

fig7: Acute axon removal causes delayed SC expansion. (A) NMJ with single-cell labeling before two-photon laser–induced axonal degeneration (SCs pseudocolored in white, magenta, and yellow). The axon was severed at the second node of Ranvier away from the synapse (white arrow indicating direction; not in frame). (B) Time-lapse recording over a period of 5 h shows AAD (note fragmentation after 1 h), which led to local SC outgrowth (orange arrowheads; shown in area boxed in A). (C and D) Fixation after 5 h and staining for BTX reveal local outgrowth along several NMJ branches (orange arrowheads in D show fixed SC channel only in the area boxed in C). The timers shown represent hours/minutes. Bars, 5 µm.
Mentions: Hence, not only neighboring SCs but also the underlying axon might suppress SC intermingling at mature NMJs. However, as Wallerian degeneration sets in with a delay, the evidence is less direct than in the case of acute laser ablation of a neighboring SC. Therefore, we sought to acutely remove axon terminals by inducing acute axonal degeneration (AAD), which fragments axon segments around a transection site within 30 min (Kerschensteiner et al., 2005). We transected single motor axons one node of Ranvier proximal of the final heminode using a two-photon laser (see Materials and methods; Galbraith and Terasaki, 2003; Turney and Lichtman, 2008). We then labeled single terminal SCs by sequential bleaching. As soon as fragmentation set in, terminal SCs appeared to engulf the resulting axonal debris. Soon after this (<4–5 h after laser axotomy), we observed the first outgrowth of small filopodial-like SC processes that invaded the neighboring territory (Fig. 7). Although this response appeared less dramatic than the response seen after SC ablation, careful inspection of image stacks of laser-axotomized NMJs still revealed fast volume expansion of SCs. As expected from the removal of axon terminals, which underlie all synaptic SCs, this expansion mostly occurred in the z direction along the optical axis of observation (unpublished data). Collectively, these data suggest that after axon removal, terminal SCs first expand into the vacated gutter and then start sending out processes to explore surrounding territory.

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