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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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Truncated central spindles alone are sufficient for cell cleavage. (A) Spindle poles, including asters and pronuclei, are removed from late anaphase or early telophase cells (a–c). The remaining central spindle fragment is then rotated ∼90° from the original equator to avoid any predeposited furrow signals (d). (B) A truncated central spindle (0 min onward), lacking astral microtubules (MT) and chromosomes (DAPI), initiates a furrow (10 min, arrows) around the spindle midzone (MT, arrows) enriched with actin filaments (AF and Overlay, arrows). (C) Furrow ingression (0–16) is normal, bearing a distinct contractile ring at the midzone of the truncated spindle (Overlay). Bars, 10 μm.
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fig2: Truncated central spindles alone are sufficient for cell cleavage. (A) Spindle poles, including asters and pronuclei, are removed from late anaphase or early telophase cells (a–c). The remaining central spindle fragment is then rotated ∼90° from the original equator to avoid any predeposited furrow signals (d). (B) A truncated central spindle (0 min onward), lacking astral microtubules (MT) and chromosomes (DAPI), initiates a furrow (10 min, arrows) around the spindle midzone (MT, arrows) enriched with actin filaments (AF and Overlay, arrows). (C) Furrow ingression (0–16) is normal, bearing a distinct contractile ring at the midzone of the truncated spindle (Overlay). Bars, 10 μm.

Mentions: Despite the ability of asters to induce cell cleavage in grasshopper spermatocytes, we found that asters are not essential for cytokinesis in these cells. We produced cells lacking asters by cutting and removing entire spindle poles from late anaphase or early telophase cells (Fig. 2 A, a–c). We then rotated the remaining central spindle fragment ∼90° from the equatorial cortex to avoid any predeposited furrow signals (Fig. 2 A, d). Despite being truncated (Fig. 2 B, 0 min onward; Fig. 2 C, 0 onward), lacking astral microtubules (MT and Overlay) and pronuclei (DAPI), the central spindle in all 21 cells produced remains well organized and initiates a cleavage furrow (Fig. 2 B, 10, arrows; Fig. 2 C, 8, arrows). The cytoskeleton in cells fixed shortly after furrowing shows the expected stage-specific structures: bundled microtubule arrays with a distinct midzone (Fig. 2 B, MT, arrows) surrounded by actin filaments (AF and Overlay, arrows). Furrow ingression (Fig. 2 C, 16) in such manipulated cells is normal, showing a well-organized central spindle and a contractile ring enriched in actin filaments at the midzone (Overlay).


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

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

Truncated central spindles alone are sufficient for cell cleavage. (A) Spindle poles, including asters and pronuclei, are removed from late anaphase or early telophase cells (a–c). The remaining central spindle fragment is then rotated ∼90° from the original equator to avoid any predeposited furrow signals (d). (B) A truncated central spindle (0 min onward), lacking astral microtubules (MT) and chromosomes (DAPI), initiates a furrow (10 min, arrows) around the spindle midzone (MT, arrows) enriched with actin filaments (AF and Overlay, arrows). (C) Furrow ingression (0–16) is normal, bearing a distinct contractile ring at the midzone of the truncated spindle (Overlay). Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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fig2: Truncated central spindles alone are sufficient for cell cleavage. (A) Spindle poles, including asters and pronuclei, are removed from late anaphase or early telophase cells (a–c). The remaining central spindle fragment is then rotated ∼90° from the original equator to avoid any predeposited furrow signals (d). (B) A truncated central spindle (0 min onward), lacking astral microtubules (MT) and chromosomes (DAPI), initiates a furrow (10 min, arrows) around the spindle midzone (MT, arrows) enriched with actin filaments (AF and Overlay, arrows). (C) Furrow ingression (0–16) is normal, bearing a distinct contractile ring at the midzone of the truncated spindle (Overlay). Bars, 10 μm.
Mentions: Despite the ability of asters to induce cell cleavage in grasshopper spermatocytes, we found that asters are not essential for cytokinesis in these cells. We produced cells lacking asters by cutting and removing entire spindle poles from late anaphase or early telophase cells (Fig. 2 A, a–c). We then rotated the remaining central spindle fragment ∼90° from the equatorial cortex to avoid any predeposited furrow signals (Fig. 2 A, d). Despite being truncated (Fig. 2 B, 0 min onward; Fig. 2 C, 0 onward), lacking astral microtubules (MT and Overlay) and pronuclei (DAPI), the central spindle in all 21 cells produced remains well organized and initiates a cleavage furrow (Fig. 2 B, 10, arrows; Fig. 2 C, 8, arrows). The cytoskeleton in cells fixed shortly after furrowing shows the expected stage-specific structures: bundled microtubule arrays with a distinct midzone (Fig. 2 B, MT, arrows) surrounded by actin filaments (AF and Overlay, arrows). Furrow ingression (Fig. 2 C, 16) in such manipulated cells is normal, showing a well-organized central spindle and a contractile ring enriched in actin filaments at the midzone (Overlay).

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