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Microtubules are the only structural constituent of the spindle apparatus required for induction of cell cleavage.

Alsop GB, Zhang D - J. Cell Biol. (2003)

Bottom Line: We show that furrow induction occurs under all circumstances, so long as sufficient microtubules are present.Microtubules, as the only spindle structural constituent, undergo dramatic, stage-specific reorganizations, radiating toward cell cortex in "metaphase," disassembling in "anaphase," and bundling into arrays in "telophase." Furrow induction usually occurs at multisites around microtubule bundles, but only those induced by sustained bundles ingress.We suggest that microtubules, regardless of source, are the only structural constituent of the spindle apparatus essential for cleavage furrow induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA.

ABSTRACT
Structural constituents of the spindle apparatus essential for cleavage induction remain undefined. Findings from various cell types using different approaches suggest the importance of all structural constituents, including asters, the central spindle, and chromosomes. In this study, we systematically dissected the role of each constituent in cleavage induction in grasshopper spermatocytes and narrowed the essential one down to bundled microtubules. Using micromanipulation, we produced "cells" containing only asters, a truncated central spindle lacking both asters and chromosomes, or microtubules alone. We show that furrow induction occurs under all circumstances, so long as sufficient microtubules are present. Microtubules, as the only spindle structural constituent, undergo dramatic, stage-specific reorganizations, radiating toward cell cortex in "metaphase," disassembling in "anaphase," and bundling into arrays in "telophase." Furrow induction usually occurs at multisites around microtubule bundles, but only those induced by sustained bundles ingress. We suggest that microtubules, regardless of source, are the only structural constituent of the spindle apparatus essential for cleavage furrow induction.

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Asters alone are sufficient for induction of cell cleavage. (A) Asters are detached from spindle poles using a microneedle (a), placed at the cell periphery (b), and secluded into a membrane pocket cut off from the mother cell (c and d). (B) Polarization microscope images. Time is given in minutes. The membrane pocket contains two prominent asters (0 min, *) with mitochondria on one side (m). The mother cell (left) bears the spindle with truncated poles. Formation of microtubule– mitochondria bundles in the pocket (31), similar to the central spindle in its mother cell, corresponds with disappearance of asters. Furrow initiation of the pocket and mother cell occurs simultaneously (63). The pocket initiates a furrow where the bundled microtubule array is proximal to the cortex (63, arrow), ingressing asymmetrically on one side of the cell (93, arrow). (C) Symmetric furrow ingression can also occur in an aster-containing membrane pocket (0–62; see Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200301073/DC1). (D) Microtubules (MT) at furrow initiation are less organized than observed in spindle-containing cells, but do exhibit a lightly stained midzone (MT, arrow) enriched with actin filaments (AF and Overlay, arrow). (E) Once ingressed, the bundled microtubule array establishes a clear midzone (MT, arrows) embraced with a tightly organized contractile ring (AF and Overlay). (F) Disassembly of astral microtubules (0, *) with nocodazole treatment (11 onward) prevents furrow induction in an aster-containing pocket (11–74) that bears only a disorganized mitochondrial mass. Although random contractions can still occur (74 onward), no furrow initiation is observed. Bars, 10 μm.
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fig1: Asters alone are sufficient for induction of cell cleavage. (A) Asters are detached from spindle poles using a microneedle (a), placed at the cell periphery (b), and secluded into a membrane pocket cut off from the mother cell (c and d). (B) Polarization microscope images. Time is given in minutes. The membrane pocket contains two prominent asters (0 min, *) with mitochondria on one side (m). The mother cell (left) bears the spindle with truncated poles. Formation of microtubule– mitochondria bundles in the pocket (31), similar to the central spindle in its mother cell, corresponds with disappearance of asters. Furrow initiation of the pocket and mother cell occurs simultaneously (63). The pocket initiates a furrow where the bundled microtubule array is proximal to the cortex (63, arrow), ingressing asymmetrically on one side of the cell (93, arrow). (C) Symmetric furrow ingression can also occur in an aster-containing membrane pocket (0–62; see Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200301073/DC1). (D) Microtubules (MT) at furrow initiation are less organized than observed in spindle-containing cells, but do exhibit a lightly stained midzone (MT, arrow) enriched with actin filaments (AF and Overlay, arrow). (E) Once ingressed, the bundled microtubule array establishes a clear midzone (MT, arrows) embraced with a tightly organized contractile ring (AF and Overlay). (F) Disassembly of astral microtubules (0, *) with nocodazole treatment (11 onward) prevents furrow induction in an aster-containing pocket (11–74) that bears only a disorganized mitochondrial mass. Although random contractions can still occur (74 onward), no furrow initiation is observed. Bars, 10 μm.

Mentions: To determine whether asters alone are sufficient for furrow induction in grasshopper spermatocytes, we produced membrane pockets that contain asters as the only spindle structural constituents and a small amount of mitochondria to provide energy. Using a microneedle, we detached asters from spindle poles in metaphase or early anaphase (Fig. 1 A, a and b) and secluded them into a membrane pocket (Fig. 1 A, c) cut off from the mother cell (Fig. 1 A, d). The pockets were monitored using a digital-enhanced polarization microscope. Several pockets were also fixed to observe the distribution of microtubules and actin filaments.


Microtubules are the only structural constituent of the spindle apparatus required for induction of cell cleavage.

Alsop GB, Zhang D - J. Cell Biol. (2003)

Asters alone are sufficient for induction of cell cleavage. (A) Asters are detached from spindle poles using a microneedle (a), placed at the cell periphery (b), and secluded into a membrane pocket cut off from the mother cell (c and d). (B) Polarization microscope images. Time is given in minutes. The membrane pocket contains two prominent asters (0 min, *) with mitochondria on one side (m). The mother cell (left) bears the spindle with truncated poles. Formation of microtubule– mitochondria bundles in the pocket (31), similar to the central spindle in its mother cell, corresponds with disappearance of asters. Furrow initiation of the pocket and mother cell occurs simultaneously (63). The pocket initiates a furrow where the bundled microtubule array is proximal to the cortex (63, arrow), ingressing asymmetrically on one side of the cell (93, arrow). (C) Symmetric furrow ingression can also occur in an aster-containing membrane pocket (0–62; see Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200301073/DC1). (D) Microtubules (MT) at furrow initiation are less organized than observed in spindle-containing cells, but do exhibit a lightly stained midzone (MT, arrow) enriched with actin filaments (AF and Overlay, arrow). (E) Once ingressed, the bundled microtubule array establishes a clear midzone (MT, arrows) embraced with a tightly organized contractile ring (AF and Overlay). (F) Disassembly of astral microtubules (0, *) with nocodazole treatment (11 onward) prevents furrow induction in an aster-containing pocket (11–74) that bears only a disorganized mitochondrial mass. Although random contractions can still occur (74 onward), no furrow initiation is observed. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172685&req=5

fig1: Asters alone are sufficient for induction of cell cleavage. (A) Asters are detached from spindle poles using a microneedle (a), placed at the cell periphery (b), and secluded into a membrane pocket cut off from the mother cell (c and d). (B) Polarization microscope images. Time is given in minutes. The membrane pocket contains two prominent asters (0 min, *) with mitochondria on one side (m). The mother cell (left) bears the spindle with truncated poles. Formation of microtubule– mitochondria bundles in the pocket (31), similar to the central spindle in its mother cell, corresponds with disappearance of asters. Furrow initiation of the pocket and mother cell occurs simultaneously (63). The pocket initiates a furrow where the bundled microtubule array is proximal to the cortex (63, arrow), ingressing asymmetrically on one side of the cell (93, arrow). (C) Symmetric furrow ingression can also occur in an aster-containing membrane pocket (0–62; see Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200301073/DC1). (D) Microtubules (MT) at furrow initiation are less organized than observed in spindle-containing cells, but do exhibit a lightly stained midzone (MT, arrow) enriched with actin filaments (AF and Overlay, arrow). (E) Once ingressed, the bundled microtubule array establishes a clear midzone (MT, arrows) embraced with a tightly organized contractile ring (AF and Overlay). (F) Disassembly of astral microtubules (0, *) with nocodazole treatment (11 onward) prevents furrow induction in an aster-containing pocket (11–74) that bears only a disorganized mitochondrial mass. Although random contractions can still occur (74 onward), no furrow initiation is observed. Bars, 10 μm.
Mentions: To determine whether asters alone are sufficient for furrow induction in grasshopper spermatocytes, we produced membrane pockets that contain asters as the only spindle structural constituents and a small amount of mitochondria to provide energy. Using a microneedle, we detached asters from spindle poles in metaphase or early anaphase (Fig. 1 A, a and b) and secluded them into a membrane pocket (Fig. 1 A, c) cut off from the mother cell (Fig. 1 A, d). The pockets were monitored using a digital-enhanced polarization microscope. Several pockets were also fixed to observe the distribution of microtubules and actin filaments.

Bottom Line: We show that furrow induction occurs under all circumstances, so long as sufficient microtubules are present.Microtubules, as the only spindle structural constituent, undergo dramatic, stage-specific reorganizations, radiating toward cell cortex in "metaphase," disassembling in "anaphase," and bundling into arrays in "telophase." Furrow induction usually occurs at multisites around microtubule bundles, but only those induced by sustained bundles ingress.We suggest that microtubules, regardless of source, are the only structural constituent of the spindle apparatus essential for cleavage furrow induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA.

ABSTRACT
Structural constituents of the spindle apparatus essential for cleavage induction remain undefined. Findings from various cell types using different approaches suggest the importance of all structural constituents, including asters, the central spindle, and chromosomes. In this study, we systematically dissected the role of each constituent in cleavage induction in grasshopper spermatocytes and narrowed the essential one down to bundled microtubules. Using micromanipulation, we produced "cells" containing only asters, a truncated central spindle lacking both asters and chromosomes, or microtubules alone. We show that furrow induction occurs under all circumstances, so long as sufficient microtubules are present. Microtubules, as the only spindle structural constituent, undergo dramatic, stage-specific reorganizations, radiating toward cell cortex in "metaphase," disassembling in "anaphase," and bundling into arrays in "telophase." Furrow induction usually occurs at multisites around microtubule bundles, but only those induced by sustained bundles ingress. We suggest that microtubules, regardless of source, are the only structural constituent of the spindle apparatus essential for cleavage furrow induction.

Show MeSH
Related in: MedlinePlus