Limits...
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.

Show MeSH

Related in: MedlinePlus

Too much Ect2-G4A inhibits furrowing. (A, B), Projections of 16 1-μm (A) or 13 2-μm (B) sections of sand dollar embryos expressing sufficient 3xGFP Ect2 GEF4A to cause cytokinesis failure. Embryos failed cytokinesis once before imaging began. (A) t = 01:30 and (B) t = 44:40 end-on views through the central spindle, where Ect2 accumulates before moving to astral microtubules, indicated by open arrowheads in A. See Supplemental Video S5. Solid arrowheads point out cortical Ect2 in the ingressing furrow. (C) Sand dollar embryo expressing 3xGFP Ect2 GEF4A (gold) and 2xmCh EMTB (blue), which has undergone multiple cycles of cytokinesis failure (18 1-μm sections). As the cell progresses through anaphase, Ect2 relocates from central spindle to overlapping astral microtubule regions, which remain after nuclear reassembly. Times are minutes:seconds after filming began.
© Copyright Policy - creative-commons
Related In: Results  -  Collection


getmorefigures.php?uid=PMC4263448&req=5

Figure 3: Too much Ect2-G4A inhibits furrowing. (A, B), Projections of 16 1-μm (A) or 13 2-μm (B) sections of sand dollar embryos expressing sufficient 3xGFP Ect2 GEF4A to cause cytokinesis failure. Embryos failed cytokinesis once before imaging began. (A) t = 01:30 and (B) t = 44:40 end-on views through the central spindle, where Ect2 accumulates before moving to astral microtubules, indicated by open arrowheads in A. See Supplemental Video S5. Solid arrowheads point out cortical Ect2 in the ingressing furrow. (C) Sand dollar embryo expressing 3xGFP Ect2 GEF4A (gold) and 2xmCh EMTB (blue), which has undergone multiple cycles of cytokinesis failure (18 1-μm sections). As the cell progresses through anaphase, Ect2 relocates from central spindle to overlapping astral microtubule regions, which remain after nuclear reassembly. Times are minutes:seconds after filming began.

Mentions: Urchin and sand dollar embryos proved acutely sensitive to increasing doses of wild-type Ect2, exhibiting cortical hypercontractility and blebbing, or even outright cleavage failure, as early as the first division (Figure 2, A and B, and Supplemental Video S4). To improve visualization of Ect2 without inducing ectopic contractions, we mutated the GEF domain (Figure 1A). SpEct2 GEF4A (as in Su et al., 2011) was tolerated at higher levels than wild-type (wt) Ect2 and exhibited similar localization (Figure 1C and Supplemental Figure S1D), although it behaves as an apparent dominant negative when expressed at high levels (see later discussion) and did not associate with the cortex as much as wt Ect2 (Figure 3). Ect2 GEF4A thus gave us a much clearer view of Ect2 association with overlapping astral microtubules in the region between the central spindle and the equatorial cortex (Figure 1C and Supplemental Videos S2 and S3); at levels sufficient to inhibit cleavage, Ect2 GEF4A appeared to stream along astral microtubules, accumulating at intersections between asters (Figure 3 and Supplemental Video S5).


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)

Too much Ect2-G4A inhibits furrowing. (A, B), Projections of 16 1-μm (A) or 13 2-μm (B) sections of sand dollar embryos expressing sufficient 3xGFP Ect2 GEF4A to cause cytokinesis failure. Embryos failed cytokinesis once before imaging began. (A) t = 01:30 and (B) t = 44:40 end-on views through the central spindle, where Ect2 accumulates before moving to astral microtubules, indicated by open arrowheads in A. See Supplemental Video S5. Solid arrowheads point out cortical Ect2 in the ingressing furrow. (C) Sand dollar embryo expressing 3xGFP Ect2 GEF4A (gold) and 2xmCh EMTB (blue), which has undergone multiple cycles of cytokinesis failure (18 1-μm sections). As the cell progresses through anaphase, Ect2 relocates from central spindle to overlapping astral microtubule regions, which remain after nuclear reassembly. Times are minutes:seconds after filming began.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4263448&req=5

Figure 3: Too much Ect2-G4A inhibits furrowing. (A, B), Projections of 16 1-μm (A) or 13 2-μm (B) sections of sand dollar embryos expressing sufficient 3xGFP Ect2 GEF4A to cause cytokinesis failure. Embryos failed cytokinesis once before imaging began. (A) t = 01:30 and (B) t = 44:40 end-on views through the central spindle, where Ect2 accumulates before moving to astral microtubules, indicated by open arrowheads in A. See Supplemental Video S5. Solid arrowheads point out cortical Ect2 in the ingressing furrow. (C) Sand dollar embryo expressing 3xGFP Ect2 GEF4A (gold) and 2xmCh EMTB (blue), which has undergone multiple cycles of cytokinesis failure (18 1-μm sections). As the cell progresses through anaphase, Ect2 relocates from central spindle to overlapping astral microtubule regions, which remain after nuclear reassembly. Times are minutes:seconds after filming began.
Mentions: Urchin and sand dollar embryos proved acutely sensitive to increasing doses of wild-type Ect2, exhibiting cortical hypercontractility and blebbing, or even outright cleavage failure, as early as the first division (Figure 2, A and B, and Supplemental Video S4). To improve visualization of Ect2 without inducing ectopic contractions, we mutated the GEF domain (Figure 1A). SpEct2 GEF4A (as in Su et al., 2011) was tolerated at higher levels than wild-type (wt) Ect2 and exhibited similar localization (Figure 1C and Supplemental Figure S1D), although it behaves as an apparent dominant negative when expressed at high levels (see later discussion) and did not associate with the cortex as much as wt Ect2 (Figure 3). Ect2 GEF4A thus gave us a much clearer view of Ect2 association with overlapping astral microtubules in the region between the central spindle and the equatorial cortex (Figure 1C and Supplemental Videos S2 and S3); at levels sufficient to inhibit cleavage, Ect2 GEF4A appeared to stream along astral microtubules, accumulating at intersections between asters (Figure 3 and Supplemental Video S5).

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