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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 climb the astral ladder in starfish. (A) One of eight cells in a starfish embryo expressing wt 3xGFP SpEct2 (gold) and 2xmCh EMTB (cyan; Supplemental Video S6). (A′, A″) Two-times magnifications of the region covering central spindle and cell equator before and midway through cleavage, with Ect2 (left), merge (middle), and microtubules (right). Arrowheads in A′ indicate astral microtubules decorated by Ect2. Arrowheads in A″ indicate Ect2-decorated microtubule bundles—the ladder—that cross the equator parallel to the spindle. (B) Kymograph from same sequence as A; times of A′ and A″ shown by vertical lines. Note the diagonal spread of Ect2 from central spindle to cell surface and that the central spindle itself grows dimmer over time as the ladder grows brighter. (C) One of 16 cells in a starfish embryo expressing wt 3xGFP SpCyk4, which appears on the central spindle and faintly on astral rays throughout the cell in anaphase (first frame) and then clears from the spindle poles outward and accumulates on astral microtubules beneath the furrow (Supplemental Video S7).
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Figure 4: Ect2 and centralspindlin climb the astral ladder in starfish. (A) One of eight cells in a starfish embryo expressing wt 3xGFP SpEct2 (gold) and 2xmCh EMTB (cyan; Supplemental Video S6). (A′, A″) Two-times magnifications of the region covering central spindle and cell equator before and midway through cleavage, with Ect2 (left), merge (middle), and microtubules (right). Arrowheads in A′ indicate astral microtubules decorated by Ect2. Arrowheads in A″ indicate Ect2-decorated microtubule bundles—the ladder—that cross the equator parallel to the spindle. (B) Kymograph from same sequence as A; times of A′ and A″ shown by vertical lines. Note the diagonal spread of Ect2 from central spindle to cell surface and that the central spindle itself grows dimmer over time as the ladder grows brighter. (C) One of 16 cells in a starfish embryo expressing wt 3xGFP SpCyk4, which appears on the central spindle and faintly on astral rays throughout the cell in anaphase (first frame) and then clears from the spindle poles outward and accumulates on astral microtubules beneath the furrow (Supplemental Video S7).

Mentions: We took advantage of the fact that starfish oocytes can be cultured after injection for several days before fertilization to allow wt 3xGFP Ect2 to accumulate to visible levels in time for first cleavage. Despite mild cortical hyperactivity, starfish embryos better tolerated extra wt Ect2 while displaying identical localization as in urchins (Figure 4A and Supplemental Video S6). As in urchin embryos, we saw little evidence of an Ect2 gradient in the nascent furrow (unless Ect2 was expressed at pathological levels) until the early blastula stage. On the other hand, Ect2 was clearly detectable on astral microtubules even in the earliest divisions: coexpression of wt 3xGFP Ect2 with 2xmCh ensconsin microtubule-binding domain (EMTB) showed that Ect2 associated with distal portions of equatorially directed astral microtubules beginning in anaphase. Ect2-decorated astral microtubules reached progressively further toward the cortex and then became brighter as they were collected by the ingressing furrow (Figure 4, A′ and A″). Kymographs of the equatorial region illustrate redistribution of Ect2 from central spindle to the asters to the membrane over time as the furrow constricts (Figure 4B and Supplemental Figure S1D).


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 climb the astral ladder in starfish. (A) One of eight cells in a starfish embryo expressing wt 3xGFP SpEct2 (gold) and 2xmCh EMTB (cyan; Supplemental Video S6). (A′, A″) Two-times magnifications of the region covering central spindle and cell equator before and midway through cleavage, with Ect2 (left), merge (middle), and microtubules (right). Arrowheads in A′ indicate astral microtubules decorated by Ect2. Arrowheads in A″ indicate Ect2-decorated microtubule bundles—the ladder—that cross the equator parallel to the spindle. (B) Kymograph from same sequence as A; times of A′ and A″ shown by vertical lines. Note the diagonal spread of Ect2 from central spindle to cell surface and that the central spindle itself grows dimmer over time as the ladder grows brighter. (C) One of 16 cells in a starfish embryo expressing wt 3xGFP SpCyk4, which appears on the central spindle and faintly on astral rays throughout the cell in anaphase (first frame) and then clears from the spindle poles outward and accumulates on astral microtubules beneath the furrow (Supplemental Video S7).
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Related In: Results  -  Collection

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Figure 4: Ect2 and centralspindlin climb the astral ladder in starfish. (A) One of eight cells in a starfish embryo expressing wt 3xGFP SpEct2 (gold) and 2xmCh EMTB (cyan; Supplemental Video S6). (A′, A″) Two-times magnifications of the region covering central spindle and cell equator before and midway through cleavage, with Ect2 (left), merge (middle), and microtubules (right). Arrowheads in A′ indicate astral microtubules decorated by Ect2. Arrowheads in A″ indicate Ect2-decorated microtubule bundles—the ladder—that cross the equator parallel to the spindle. (B) Kymograph from same sequence as A; times of A′ and A″ shown by vertical lines. Note the diagonal spread of Ect2 from central spindle to cell surface and that the central spindle itself grows dimmer over time as the ladder grows brighter. (C) One of 16 cells in a starfish embryo expressing wt 3xGFP SpCyk4, which appears on the central spindle and faintly on astral rays throughout the cell in anaphase (first frame) and then clears from the spindle poles outward and accumulates on astral microtubules beneath the furrow (Supplemental Video S7).
Mentions: We took advantage of the fact that starfish oocytes can be cultured after injection for several days before fertilization to allow wt 3xGFP Ect2 to accumulate to visible levels in time for first cleavage. Despite mild cortical hyperactivity, starfish embryos better tolerated extra wt Ect2 while displaying identical localization as in urchins (Figure 4A and Supplemental Video S6). As in urchin embryos, we saw little evidence of an Ect2 gradient in the nascent furrow (unless Ect2 was expressed at pathological levels) until the early blastula stage. On the other hand, Ect2 was clearly detectable on astral microtubules even in the earliest divisions: coexpression of wt 3xGFP Ect2 with 2xmCh ensconsin microtubule-binding domain (EMTB) showed that Ect2 associated with distal portions of equatorially directed astral microtubules beginning in anaphase. Ect2-decorated astral microtubules reached progressively further toward the cortex and then became brighter as they were collected by the ingressing furrow (Figure 4, A′ and A″). Kymographs of the equatorial region illustrate redistribution of Ect2 from central spindle to the asters to the membrane over time as the furrow constricts (Figure 4B and Supplemental Figure S1D).

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