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 spindleposition 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.
During the 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 anaphase spindle rocking, these pulling forces are regulated by the force generator dynamics, which are in turn consequent of mitotic progression. We found a novel, additional, regulation of these forces by the spindle position. It controls astral microtubule availability at the cortex, on which the active force generators can pull. Importantly, this positional control relies on the polarity dependent LET-99 cortical band, which restricts or concentrates generators to a posterior crescent. We ascribed this control to the microtubule dynamics at the cortex. Indeed, in mapping the cortical contacts, we found a correlation between the centrosome-cortex distance and the microtubule contact density. In turn, it modulates pulling force generator activity. We modelled this control, predicting and experimentally validating that the posterior crescent extent controlled where the anaphase oscillations started, in addition to mitotic progression. Finally, we propose that spatially restricting force generator to a posterior crescent sets the spindle's final position, reflecting polarity through the LET-99 dependent restriction of force generators to a posterior crescent . This regulation superimposes that of force generator processivity . This novel control confers a low dependence on microtubule and active force generator exact numbers or dynamics, provided that they exceed the threshold needed for posterior displacement . Interestingly, this robustness originates in cell mechanics rather than biochemical networks.
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Background: During
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anaphase
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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
in turn consequent of mitotic progression. We found a novel, additional, regulation of these forces by the spindle position. It controls astral microtubule availability at the cortex, on which the active force generators can pull. Importantly, this positional control relies on the polarity dependent LET-99 cortical band, which restricts or concentrates generators to a posterior crescent. We ascribed this control to the
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contacts
cortical contacts,
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This density in turn
In turn, it
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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 spindleposition regulates the rapid increase in forces needed for anaphase oscillation and positioning through the spatial modulation of microtubule-cortex contacts
modelled this control, predicting and experimentally validating that the posterior crescent extent controlled where the anaphase oscillations started, in addition to mitotic progression. Finally, we propose that spatially restricting force generator to a posterior crescent sets the spindle's final position, reflecting polarity through the LET-99 dependent restriction of force generators to a posterior crescent
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, putatively linked to the cell cycle
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resistance to variations in zygote geometry and dynamics of cortical force generators
a low dependence on microtubule and active force generator exact numbers or dynamics, provided that they exceed the threshold needed for posterior displacement