Background: The correct positioning of the mitotic spindle during the asymmetric division of the nematode C. elegans zygote relies on the combination of centering and corticalpulling forces. These forces, revealed by centrosome anaphase oscillations, are regulated through the dynamics of force generators, related to mitosis progression. Recently, we reported the control of oscillation onset by the posterior spindle pole position in related speciesC. briggsae, necessitating a re-evaluation of the role of astral microtubules dynamics. Results: After exhibiting such a positional switch in C. elegans, we mapped the microtubule ends at the cortex and observed a correlation between the proximity of the centrosomes and the density of microtubule contacts. To explore the functional consequences, we extended the tug-of-war model and successfully accounted for the positional switch. We predicted and experimentally validated that the control of oscillation onset was robust to changes in cell geometry or maximum number of attached force generators. We also predicted that the final position of the posterior centrosome and thus the spindle has a reduced dependence upon the force generator dynamics or number . Conclusion: The outburst of forces responsible of spindle anaphase oscillations and positioning is regulated by the spindle position through the spatial modulation of microtubule contactsat the cortex . This regulation superimposes that of force generator processivity  putatively linked to the cell cycle. This novel control provides robustness to variations in zygote geometry or detailed properties of cortical force generators  .
Background: During asymmetric division of the Caenorhabditis elegans nematode zygote, the polarity cues distribution and daughter cell fates depend on the correct positioning of the mitotic spindle which results from both centering and cortical pulling forces. Revealed by spindle rocking, these pulling forces are regulated by the force generator dynamics, which are related to mitosis progression. This may be combined with a second regulation, this one by the posterior spindle pole position , which can be seen when comparing related species. Results: After delaying anaphase onset, we identified a positional pulling force regulation in C. elegans, which we ascribed to microtubule dynamics at the cortex . Indeed, in mapping the contacts we found a correlation between the centrosome-cortex distance and the microtubule contact density. This density in turn modulates pulling force generator activity. We expanded our model of spindle rocking and predicted then experimentally validated that the oscillation onset position resists changes in cellular geometry and number of force generators. Consistent with final spindle position measurements, this new model accounts for a lower dependence on force generator dynamics and quantities than predicted by the previous model . Conclusion: The spindle position regulates the rapid increase in forces needed for anaphase oscillation and positioning through the spatial modulation of microtubule-cortex contacts . This regulation superimposes that of force generator processivity , putatively linked to the cell cycle. This novel control confers resistance to variations in zygote geometry and dynamics of cortical force generators . Interestingly, this robustness originates in cell mechanics rather than biochemical networks .
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The correct positioning of the mitotic spindle during the
During
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nematode C. elegans zygote relies on the combination of centering and corticalpulling forces. These forces, revealed by centrosome anaphase oscillations, are regulated through the dynamics of force generators,
Caenorhabditis elegans nematode zygote, the polarity cues distribution and daughter cell fates depend on the correct positioning of the mitotic spindle which results from both centering and cortical pulling forces. Revealed by spindle rocking, these pulling forces are regulated by the force generator dynamics, which are
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Recently, we reported the control of oscillation onset
This may be combined with a second regulation, this one
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in related speciesC. briggsae, necessitating a re-evaluation of the role of astral microtubules dynamics.
, which can be seen when comparing related species.
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exhibiting such a positional switch
delaying anaphase onset, we identified a positional pulling force regulation
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we mapped the microtubule ends
which we ascribed to microtubule dynamics
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and observed
. Indeed, in mapping the contacts we found
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proximity of the centrosomes and the density of microtubule contacts. To explore the functional consequences, we extended the tug-of-war model and successfully accounted for the positional switch. We predicted and
centrosome-cortex distance and the microtubule contact density. This density in turn modulates pulling force generator activity. We expanded our model of spindle rocking and predicted then
R
control of oscillation onset was robust to changes in cell geometry or maximum number of attached
oscillation onset position resists changes in cellular geometry and number of
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We also predicted that the final position of the posterior centrosome and thus the spindle has a reduced dependence upon the
Consistent with final spindle position measurements, this new model accounts for a lower dependence on
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or number
and quantities than predicted by the previous model
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outburst of forces responsible of spindle anaphase oscillations and positioning is regulated by the spindle position
spindle position regulates the rapid increase in forces needed for anaphase oscillation and positioning
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microtubule contactsat the cortex
microtubule-cortex contacts
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,
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provides robustness
confers resistance
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or detailed properties
and dynamics
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. Interestingly, this robustness originates in cell mechanics rather than biochemical networks