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An astral simulacrum of the central spindle accounts for normal, spindle-less, and anucleate cytokinesis in echinoderm embryos.

Su KC, Bement WM, Petronczki M, von Dassow G - Mol. Biol. Cell (2014)

Bottom Line: Here we describe the behavior and function of Ect2 in echinoderm embryos, showing that Ect2 migrates from spindle midzone to astral microtubules in anaphase and that Ect2 shapes the pattern of Rho activation in incipient furrows.In all these cases, the cell assembles essentially the same cytokinetic signaling ensemble—opposed astral microtubules decorated with Ect2 and Cyk4.We conclude that if multiple signals contribute to furrow induction in echinoderm embryos, they likely converge on the same signaling ensemble on an analogous cytoskeletal scaffold.

View Article: PubMed Central - PubMed

Affiliation: Oregon Institute of Marine Biology, Charleston, OR 97420 Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom.

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Ect2 and centralspindlin are associated with secondary furrows in toroidal cells. Starfish zygote (A) and one of four cells (B) expressing wt 3xGFP Ect2 (gold) and 2xmCh EMTB (cyan) and perforated with a 50-μm glass bead (Supplemental Video S9). Top, first division after perforation; bottom, next division of resulting binucleate, U-shaped cell. Inset in A, 2× magnification of the secondary furrow region (boxed); insets 1 and 2 in B, primary and secondary furrows. (C) One of two cells in a starfish embryo expressing wt 3xGFP Cyk4 and perforated as in A and B (Supplemental Video S10); inset, secondary furrow region. Open arrowheads mark primary (spindle-crossing) furrows; solid arrowheads mark secondary furrows that pass between two asters.
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Figure 7: Ect2 and centralspindlin are associated with secondary furrows in toroidal cells. Starfish zygote (A) and one of four cells (B) expressing wt 3xGFP Ect2 (gold) and 2xmCh EMTB (cyan) and perforated with a 50-μm glass bead (Supplemental Video S9). Top, first division after perforation; bottom, next division of resulting binucleate, U-shaped cell. Inset in A, 2× magnification of the secondary furrow region (boxed); insets 1 and 2 in B, primary and secondary furrows. (C) One of two cells in a starfish embryo expressing wt 3xGFP Cyk4 and perforated as in A and B (Supplemental Video S10); inset, secondary furrow region. Open arrowheads mark primary (spindle-crossing) furrows; solid arrowheads mark secondary furrows that pass between two asters.

Mentions: We next tested whether Ect2 and centralspindlin are localized to furrows that form between two asters without a spindle between them (“secondary” furrows). The classic instance is the toroidal cell, which, as described originally by Rappaport (1961), first cleaves to make a binucleate, U-shaped cell; at second mitosis, it cleaves from one to four cells with two furrows crossing spindles and one that passes between two asters. We perforated Ect2- or Cyk4-expressing starfish zygotes or blastomeres from the 2- to 16-cell stage with a 40- to 60-μm glass bead. Ect2 consistently appeared, albeit more faintly than in the primary furrows, in the overlap zone where a secondary furrow ingressed, becoming concentrated to a midbody in all cases in which the secondary furrow completed (Figure 7, A and B, and Supplemental Video S9). Cyk4 always recruited robustly to the secondary furrow (Figure 7C and Supplemental Video S10). Of interest, perforated cells expressing Ect2 or Cyk4 also displayed elevated cortical contractility, and occasionally an ingressing furrow, on the far side of the torus during the first mitosis (Supplemental Videos S9 and S10); although we did not unambiguously detect Ect2 in such cases, Cyk4 consistently decorated distal portions of astral microtubules on the far side of the torus, albeit much less well focused than at second mitosis (Figure 7C and Supplemental Video S10).


An astral simulacrum of the central spindle accounts for normal, spindle-less, and anucleate cytokinesis in echinoderm embryos.

Su KC, Bement WM, Petronczki M, von Dassow G - Mol. Biol. Cell (2014)

Ect2 and centralspindlin are associated with secondary furrows in toroidal cells. Starfish zygote (A) and one of four cells (B) expressing wt 3xGFP Ect2 (gold) and 2xmCh EMTB (cyan) and perforated with a 50-μm glass bead (Supplemental Video S9). Top, first division after perforation; bottom, next division of resulting binucleate, U-shaped cell. Inset in A, 2× magnification of the secondary furrow region (boxed); insets 1 and 2 in B, primary and secondary furrows. (C) One of two cells in a starfish embryo expressing wt 3xGFP Cyk4 and perforated as in A and B (Supplemental Video S10); inset, secondary furrow region. Open arrowheads mark primary (spindle-crossing) furrows; solid arrowheads mark secondary furrows that pass between two asters.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 7: Ect2 and centralspindlin are associated with secondary furrows in toroidal cells. Starfish zygote (A) and one of four cells (B) expressing wt 3xGFP Ect2 (gold) and 2xmCh EMTB (cyan) and perforated with a 50-μm glass bead (Supplemental Video S9). Top, first division after perforation; bottom, next division of resulting binucleate, U-shaped cell. Inset in A, 2× magnification of the secondary furrow region (boxed); insets 1 and 2 in B, primary and secondary furrows. (C) One of two cells in a starfish embryo expressing wt 3xGFP Cyk4 and perforated as in A and B (Supplemental Video S10); inset, secondary furrow region. Open arrowheads mark primary (spindle-crossing) furrows; solid arrowheads mark secondary furrows that pass between two asters.
Mentions: We next tested whether Ect2 and centralspindlin are localized to furrows that form between two asters without a spindle between them (“secondary” furrows). The classic instance is the toroidal cell, which, as described originally by Rappaport (1961), first cleaves to make a binucleate, U-shaped cell; at second mitosis, it cleaves from one to four cells with two furrows crossing spindles and one that passes between two asters. We perforated Ect2- or Cyk4-expressing starfish zygotes or blastomeres from the 2- to 16-cell stage with a 40- to 60-μm glass bead. Ect2 consistently appeared, albeit more faintly than in the primary furrows, in the overlap zone where a secondary furrow ingressed, becoming concentrated to a midbody in all cases in which the secondary furrow completed (Figure 7, A and B, and Supplemental Video S9). Cyk4 always recruited robustly to the secondary furrow (Figure 7C and Supplemental Video S10). Of interest, perforated cells expressing Ect2 or Cyk4 also displayed elevated cortical contractility, and occasionally an ingressing furrow, on the far side of the torus during the first mitosis (Supplemental Videos S9 and S10); although we did not unambiguously detect Ect2 in such cases, Cyk4 consistently decorated distal portions of astral microtubules on the far side of the torus, albeit much less well focused than at second mitosis (Figure 7C and Supplemental Video S10).

Bottom Line: Here we describe the behavior and function of Ect2 in echinoderm embryos, showing that Ect2 migrates from spindle midzone to astral microtubules in anaphase and that Ect2 shapes the pattern of Rho activation in incipient furrows.In all these cases, the cell assembles essentially the same cytokinetic signaling ensemble—opposed astral microtubules decorated with Ect2 and Cyk4.We conclude that if multiple signals contribute to furrow induction in echinoderm embryos, they likely converge on the same signaling ensemble on an analogous cytoskeletal scaffold.

View Article: PubMed Central - PubMed

Affiliation: Oregon Institute of Marine Biology, Charleston, OR 97420 Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom.

Show MeSH
Related in: MedlinePlus