An astral simulacrum of the central spindle accounts for normal, spindle-less, and anucleate cytokinesis in echinoderm embryos.
Bottom Line: Although the nature, origin, and variety of such cues have long been obscure, one component is certainly the Rho activator Ect2.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.
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
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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).
Affiliation: Oregon Institute of Marine Biology, Charleston, OR 97420 Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom.