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Contraction and polymerization cooperate to assemble and close actomyosin rings around Xenopus oocyte wounds.

Mandato CA, Bement WM - J. Cell Biol. (2001)

Bottom Line: The zone forms before the ring and can be uncoupled from the ring by inhibition of cortical flow and contractility.However, contractility and the contractile ring are required for the stability and forward movement of the zone, as revealed by changes in zone dynamics after disruption of contractility and flow, or experimentally induced breakage of the contractile ring.We conclude that wound-induced contractile arrays are provided with their characteristic flexibility, speed, and strength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable contractile actomyosin ring.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Wisconsin, Madison, WI 53706, USA. camandato@facstaff.wisc.edu

ABSTRACT
Xenopus oocytes assemble an array of F-actin and myosin 2 around plasma membrane wounds. We analyzed this process in living oocytes using confocal time-lapse (four-dimensional) microscopy. Closure of wounds requires assembly and contraction of a classic "contractile ring" composed of F-actin and myosin 2. However, this ring works in concert with a 5-10-microm wide "zone" of localized actin and myosin 2 assembly. The zone forms before the ring and can be uncoupled from the ring by inhibition of cortical flow and contractility. However, contractility and the contractile ring are required for the stability and forward movement of the zone, as revealed by changes in zone dynamics after disruption of contractility and flow, or experimentally induced breakage of the contractile ring. We conclude that wound-induced contractile arrays are provided with their characteristic flexibility, speed, and strength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable contractile actomyosin ring.

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Breakage of the contractile ring destabilizes the zone of actin polymerization. Double-label images from 4D video of oocyte injected with OG-actin and TMR–myosin 2 and then subjected to cauterization wounding. See Video 12. Hatched line indicates burnt area of cytoplasm. Initially actin is present around wound as typical zone of polymerization. 6 min after start of imaging cortical flow has commenced, as revealed by development of dark halo around wound. The contractile ring is visible as a tight red-yellow ring within broader green zone of polymerization. The ring encounters edge of cauterized cytoplasm (arrow), stops movement, and begins to stretch. The zone of actin polymerization is broader in this region (arrowheads). By 10 min the contractile ring has broken, two recoiling free edges are visible (arrows) and zone widens and dims locally near break. At later time points (14:30) the edge of the spreading zone (arrowhead) is only barely visible near the original break site, whereas the spreading itself (double arrowheads) is apparently following the retreating free edges of the broken contractile ring (arrows). By 21 min the zone is almost gone near the original break point, but by 30 min, a new zone has assembled (arrowheads). The supplemental video is available at http://www.jcb.org/content/vol154/issue4.
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fig8: Breakage of the contractile ring destabilizes the zone of actin polymerization. Double-label images from 4D video of oocyte injected with OG-actin and TMR–myosin 2 and then subjected to cauterization wounding. See Video 12. Hatched line indicates burnt area of cytoplasm. Initially actin is present around wound as typical zone of polymerization. 6 min after start of imaging cortical flow has commenced, as revealed by development of dark halo around wound. The contractile ring is visible as a tight red-yellow ring within broader green zone of polymerization. The ring encounters edge of cauterized cytoplasm (arrow), stops movement, and begins to stretch. The zone of actin polymerization is broader in this region (arrowheads). By 10 min the contractile ring has broken, two recoiling free edges are visible (arrows) and zone widens and dims locally near break. At later time points (14:30) the edge of the spreading zone (arrowhead) is only barely visible near the original break site, whereas the spreading itself (double arrowheads) is apparently following the retreating free edges of the broken contractile ring (arrows). By 21 min the zone is almost gone near the original break point, but by 30 min, a new zone has assembled (arrowheads). The supplemental video is available at http://www.jcb.org/content/vol154/issue4.

Mentions: The fact that actin and myosin 2 accumulated around wound borders when contraction and cortical flow were prevented demonstrated that neither contractility nor the contractile ring are required for formation of the polymerization zone. However, the fact that the zone eventually disappeared in the presence of NEM-S1 and WGA suggested that contractility, the contractile ring, or both help maintain the zone. To test this notion, oocytes were injected with both OG-actin and TMR–myosin 2, and then subjected to wound cauterization. The TMR–myosin 2 allowed identification of the contractile ring within the broader zone of polymerization revealed by OG-actin (Fig. 4 A). Upon contact with the cauterized region, one portion of the contractile ring ceases movement, becomes stretched, and then snaps (Fig. 8 and Video 12). The local stopping and stretching of the contractile ring was accompanied by local stopping and broadening of the polymerization zone (Fig. 8 and Video 12). Upon breakage of the contractile ring, the zone transiently disappeared and then reappeared as an arc extending off of the rest of the actomyosin array around the wound, but distal from the wound edge. Thus, the contractile ring is required for forward movement of the zone and to keep it focussed around the edge of the wound. The supplemental videos are available at http://www.jcb.org/content/vol154/issue4.


Contraction and polymerization cooperate to assemble and close actomyosin rings around Xenopus oocyte wounds.

Mandato CA, Bement WM - J. Cell Biol. (2001)

Breakage of the contractile ring destabilizes the zone of actin polymerization. Double-label images from 4D video of oocyte injected with OG-actin and TMR–myosin 2 and then subjected to cauterization wounding. See Video 12. Hatched line indicates burnt area of cytoplasm. Initially actin is present around wound as typical zone of polymerization. 6 min after start of imaging cortical flow has commenced, as revealed by development of dark halo around wound. The contractile ring is visible as a tight red-yellow ring within broader green zone of polymerization. The ring encounters edge of cauterized cytoplasm (arrow), stops movement, and begins to stretch. The zone of actin polymerization is broader in this region (arrowheads). By 10 min the contractile ring has broken, two recoiling free edges are visible (arrows) and zone widens and dims locally near break. At later time points (14:30) the edge of the spreading zone (arrowhead) is only barely visible near the original break site, whereas the spreading itself (double arrowheads) is apparently following the retreating free edges of the broken contractile ring (arrows). By 21 min the zone is almost gone near the original break point, but by 30 min, a new zone has assembled (arrowheads). The supplemental video is available at http://www.jcb.org/content/vol154/issue4.
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Related In: Results  -  Collection

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fig8: Breakage of the contractile ring destabilizes the zone of actin polymerization. Double-label images from 4D video of oocyte injected with OG-actin and TMR–myosin 2 and then subjected to cauterization wounding. See Video 12. Hatched line indicates burnt area of cytoplasm. Initially actin is present around wound as typical zone of polymerization. 6 min after start of imaging cortical flow has commenced, as revealed by development of dark halo around wound. The contractile ring is visible as a tight red-yellow ring within broader green zone of polymerization. The ring encounters edge of cauterized cytoplasm (arrow), stops movement, and begins to stretch. The zone of actin polymerization is broader in this region (arrowheads). By 10 min the contractile ring has broken, two recoiling free edges are visible (arrows) and zone widens and dims locally near break. At later time points (14:30) the edge of the spreading zone (arrowhead) is only barely visible near the original break site, whereas the spreading itself (double arrowheads) is apparently following the retreating free edges of the broken contractile ring (arrows). By 21 min the zone is almost gone near the original break point, but by 30 min, a new zone has assembled (arrowheads). The supplemental video is available at http://www.jcb.org/content/vol154/issue4.
Mentions: The fact that actin and myosin 2 accumulated around wound borders when contraction and cortical flow were prevented demonstrated that neither contractility nor the contractile ring are required for formation of the polymerization zone. However, the fact that the zone eventually disappeared in the presence of NEM-S1 and WGA suggested that contractility, the contractile ring, or both help maintain the zone. To test this notion, oocytes were injected with both OG-actin and TMR–myosin 2, and then subjected to wound cauterization. The TMR–myosin 2 allowed identification of the contractile ring within the broader zone of polymerization revealed by OG-actin (Fig. 4 A). Upon contact with the cauterized region, one portion of the contractile ring ceases movement, becomes stretched, and then snaps (Fig. 8 and Video 12). The local stopping and stretching of the contractile ring was accompanied by local stopping and broadening of the polymerization zone (Fig. 8 and Video 12). Upon breakage of the contractile ring, the zone transiently disappeared and then reappeared as an arc extending off of the rest of the actomyosin array around the wound, but distal from the wound edge. Thus, the contractile ring is required for forward movement of the zone and to keep it focussed around the edge of the wound. The supplemental videos are available at http://www.jcb.org/content/vol154/issue4.

Bottom Line: The zone forms before the ring and can be uncoupled from the ring by inhibition of cortical flow and contractility.However, contractility and the contractile ring are required for the stability and forward movement of the zone, as revealed by changes in zone dynamics after disruption of contractility and flow, or experimentally induced breakage of the contractile ring.We conclude that wound-induced contractile arrays are provided with their characteristic flexibility, speed, and strength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable contractile actomyosin ring.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Wisconsin, Madison, WI 53706, USA. camandato@facstaff.wisc.edu

ABSTRACT
Xenopus oocytes assemble an array of F-actin and myosin 2 around plasma membrane wounds. We analyzed this process in living oocytes using confocal time-lapse (four-dimensional) microscopy. Closure of wounds requires assembly and contraction of a classic "contractile ring" composed of F-actin and myosin 2. However, this ring works in concert with a 5-10-microm wide "zone" of localized actin and myosin 2 assembly. The zone forms before the ring and can be uncoupled from the ring by inhibition of cortical flow and contractility. However, contractility and the contractile ring are required for the stability and forward movement of the zone, as revealed by changes in zone dynamics after disruption of contractility and flow, or experimentally induced breakage of the contractile ring. We conclude that wound-induced contractile arrays are provided with their characteristic flexibility, speed, and strength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable contractile actomyosin ring.

Show MeSH
Related in: MedlinePlus