Stronger net posterior cortical forces and asymmetric microtubule arrays produce simultaneous centration and rotation of the pronuclear complex in the early<i>Caenorhabditis elegans</i>embryo

Coffman, Valerie C.; McDermott, Matthew B. A.; Shtylla, Blerta; Dawes, Adriana T.

doi:10.1091/mbc.e16-06-0430

Cited by 12 publications

(17 citation statements)

References 55 publications

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“…By precise level, we mean that minimal numbers of microtubules and active force generators are required to ensure posterior displacement, but beyond that constraint, the values do not need to be finely tuned, and modest variations can be buffered. Understanding robustness by accounting for a spatial distribution and regulation of force generation is in its principle similar to the contribution of both the asymmetric microtubule array and a LET-99 band to force regulation during centration and orientation of the pronuclei-centrosome complex (59). Indeed, we propose here that the mechanism linking the LET-99 domain and final spindle position relies on spatial restriction of active force generators to a posteriormost crescent.…”

Section: Discussionmentioning

confidence: 69%

Microtubule Feedback and LET-99-Dependent Control of Pulling Forces Ensure Robust Spindle Position

Bouvrais

Chesneau

Pastezeur

et al. 2018

Biophysical Journal

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During asymmetric division of the Caenorhabditis elegans zygote, to properly distribute cell fate determinants, the mitotic spindle is asymmetrically localized by a combination of centering and cortical-pulling microtubule-mediated forces, the dynamics of the latter being regulated by mitotic progression. Here, we show a, to our knowledge, novel and additional regulation of these forces by spindle position itself. For that, we observed the onset of transverse spindle oscillations, which reflects the burst of anaphase pulling forces. After delaying anaphase onset, we found that the position at which the spindle starts to oscillate was unchanged compared to control embryos and uncorrelated to anaphase onset. In mapping the cortical microtubule dynamics, we measured a steep increase in microtubule contact density after the posterior centrosome reached the critical position of 70% of embryo length, strongly suggesting the presence of a positional switch for spindle oscillations. Expanding a previous model based on a force-generator temporal control, we implemented this positional switch and observed that the large increase in microtubule density accounted for the pulling force burst. Thus, we propose that the spindle position influences the cortical availability of microtubules on which the active force generators, controlled by cell cycle progression, can pull. Importantly, we found that this positional control relies on the polarity-dependent LET-99 cortical band, the boundary of which could be probed by microtubules. This dual positional and temporal control well accounted for our observation that the oscillation onset position resists changes in cellular geometry and moderate variations in the active force generator number. Finally, our model suggests that spindle position at mitosis end is more sensitive to the polarity factor LET-99, which restricts the region of active force generators to a posterior-most region, than to microtubule number or force generator number/activity. Overall, we show that robustness in spindle positioning originates in cell mechanics rather than biochemical networks.

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Section: Discussionmentioning

confidence: 69%

Microtubule Feedback and LET-99-Dependent Control of Pulling Forces Ensure Robust Spindle Position

Bouvrais

Chesneau

Pastezeur

et al. 2018

Biophysical Journal

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“…We found that p150 CAP-Gly mutants have defects in the centration and rotation of the NCC, which consists of the two centrosomes and the associated female and male pronucleus. Experimental work and biophysical modelling support the idea that centration forces in the one-cell embryo are generated by dyneinmediated cytoplasmic pulling (Kimura & Onami, 2005;Kimura & Kimura, 2011;Shinar et al, 2011), although a centration/rotation model based on cortical pulling forces has also been proposed (Coffman et al, 2016). In the cytoplasmic pulling model, dynein works against viscous drag as it transports small organelles (e.g.…”

Section: Discussionmentioning

confidence: 97%

Dynactin binding to tyrosinated microtubules promotes centrosome centration inC. elegansby enhancing dynein-mediated organelle transport

Barbosa¹,

Duro²,

Cheerambathur

et al. 2017

Preprint

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The microtubule-based motor dynein generates pulling forces for centrosome centration and mitotic spindle positioning in animal cells. How the essential dynein activator dynactin regulates these functions of the motor is incompletely understood.Here, we dissect the role of dynactin's microtubule binding activity, located in p150's CAPGly domain and an adjacent basic patch, in the C. elegans zygote. Using precise mutants engineered by genome editing, we show that microtubule tip tracking of dynein-dynactin is dispensable for targeting the motor to the cell cortex and for generating cortical pulling forces. Instead, p150 CAP-Gly mutants inhibit cytoplasmic pulling forces responsible for centration of centrosomes and attached pronuclei. The centration defects are mimicked by mutations of the C-terminal tyrosine of a-tubulin, and both p150 CAP-Gly and tubulin tyrosination mutants decrease the frequency of organelle transport from the cell periphery towards centrosomes during centration. In light of recent work on dynein-dynactin motility in vitro, our results suggest that p150 GAP-Gly domain binding to tyrosinated microtubules promotes initiation of dynein-mediated organelle transport in the dividing embryo, and that this function of dynactin is important for generating robust cytoplasmic pulling forces for centrosome centration.

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“…We found that p150 dnc-1 CAP-Gly mutants have defects in the centration and rotation of the NCC, which consists of the two centrosomes and the associated female and male pronucleus. Experimental work and biophysical modelling support the idea that centration forces in the one-cell embryo are generated by dynein-mediated cytoplasmic pulling [ 5 , 63 , 64 ], although a centration/rotation model based on cortical pulling has also been proposed [ 68 ]. In the cytoplasmic pulling model, dynein works against viscous drag as it transports small organelles (e.g.…”

Section: Discussionmentioning

confidence: 99%

Dynactin binding to tyrosinated microtubules promotes centrosome centration in C. elegans by enhancing dynein-mediated organelle transport

et al. 2017

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The microtubule-based motor dynein generates pulling forces for centrosome centration and mitotic spindle positioning in animal cells. How the essential dynein activator dynactin regulates these functions of the motor is incompletely understood. Here, we dissect the role of dynactin's microtubule binding activity, located in the p150 CAP-Gly domain and an adjacent basic patch, in the C. elegans zygote. Analysis of p150 mutants engineered by genome editing suggests that microtubule tip tracking of dynein-dynactin is dispensable for targeting the motor to the cell cortex and for generating robust cortical pulling forces. Instead, mutations in p150's CAP-Gly domain inhibit cytoplasmic pulling forces responsible for centration of centrosomes and attached pronuclei. The centration defects are mimicked by mutations of α-tubulin's C-terminal tyrosine, and both p150 CAP-Gly and tubulin tyrosine mutants decrease the frequency of early endosome transport from the cell periphery towards centrosomes during centration. Our results suggest that p150 GAP-Gly domain binding to tyrosinated microtubules promotes initiation of dynein-mediated organelle transport in the dividing one-cell embryo, and that this function of p150 is critical for generating cytoplasmic pulling forces for centrosome centration.

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Stronger net posterior cortical forces and asymmetric microtubule arrays produce simultaneous centration and rotation of the pronuclear complex in the earlyCaenorhabditis elegansembryo

Abstract: Experimental and theoretical approaches are used to demonstrate the importance of asymmetries in microtubule arrays and cortical pulling forces mediated by dynein in positioning the pronuclear complex before nuclear envelope breakdown in the early Caenorhabditis elegans embryo.

Cited by 12 publications

References 55 publications

Microtubule Feedback and LET-99-Dependent Control of Pulling Forces Ensure Robust Spindle Position

Microtubule Feedback and LET-99-Dependent Control of Pulling Forces Ensure Robust Spindle Position

Dynactin binding to tyrosinated microtubules promotes centrosome centration inC. elegansby enhancing dynein-mediated organelle transport

Dynactin binding to tyrosinated microtubules promotes centrosome centration in C. elegans by enhancing dynein-mediated organelle transport

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