TY - JOUR T1 - Astral microtubule dynamics regulate anaphase oscillation onset and set a robust final position of the <em>C. elegans</em> zygote spindle JF - bioRxiv DO - 10.1101/103937 SP - 103937 AU - H. Bouvrais AU - L. Chesneau AU - S. Pastezeur AU - M. Delattre AU - J. Pécréaux Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/01/28/103937.abstract N2 - 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 cortical-pulling forces. These forces, revealed by centrosome anaphase oscillations, are regulated through the dynamics of force generators, related to mitosis progression. Recently, we have presented the control of oscillation onset by the posterior spindle pole position in related species C. 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 contacts at 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.HighlightsMicrotubule contacts at the cortex concentrate at regions close to the centrosomes.This regulates pulling forces and creates a positional switch on oscillation onset.The onset position is robust to changes in embryo length or force generator dynamics.The final centrosome position is robust to changes in generator number or dynamics.eTOC Blurb Observing inhomogeneous MT contact density at cortex, Bouvrais et al. propose that the posterior centrosome position regulates engagement of pulling force generators, creating a positional switch on oscillation onset. This, and thus final centrosome position, is robust to variation in number or dynamics of force generators. ER -