Cell division orientation is thought to result from a competition between cell geometry and polarity domains controlling the position of the mitotic spindle during mitosis. Depending on the level of cell shape anisotropy or the strength of the polarity domain, one dominates the other and determines the orientation of the spindle. Whether and how such competition is also at work to determine unequal cell division (UCD), producing daughter cells of different size, remains unclear. Here, we show that cell geometry and polarity domains cooperate, rather than compete, in positioning the cleavage plane during UCDs in early ascidian embryos. We found that the UCDs and their orientation at the ascidian third cleavage rely on the spindle tilting in an anisotropic cell shape, and cortical polarity domains exerting different effects on spindle astral microtubules. By systematically varying mitotic cell shape, we could modulate the effect of attractive and repulsive polarity domains and consequently generate predicted daughter cell size asymmetries and position. We therefore propose that the spindle position during UCD is set by the combined activities of cell geometry and polarity domains, where cell geometry modulates the effect of cortical polarity domain(s).
We thank members of the Heisenberg and McDougall groups for technical advice and discussion. We are grateful to the Bioimaging and Nanofabrication facilities of IST Austria and the Imaging Platform (PIM) and animal facility (CRB) of Institut de la Mer de Villefranche (IMEV), which is supported by EMBRC-France, whose French state funds are managed by the ANR within the Investments of the Future program under reference ANR-10-INBS-0, for continuous support. This work was supported by a collaborative grant from the French Government funding agency Agence National de la Recherche to McDougall (ANR 'MorCell': ANR-17-CE 13-0028) and the Austrian Science Fund to Heisenberg (FWF: I 3601-B27).
Godard BG, Dumollard R, Heisenberg C-PJ, Mcdougall A. Combined effect of cell geometry and polarity domains determines the orientation of unequal division. eLife. 2021;10. doi:10.7554/eLife.75639
Godard, B. G., Dumollard, R., Heisenberg, C.-P. J., & Mcdougall, A. (2021). Combined effect of cell geometry and polarity domains determines the orientation of unequal division. ELife. eLife Sciences Publications. https://doi.org/10.7554/eLife.75639
Godard, Benoit G, Remi Dumollard, Carl-Philipp J Heisenberg, and Alex Mcdougall. “Combined Effect of Cell Geometry and Polarity Domains Determines the Orientation of Unequal Division.” ELife. eLife Sciences Publications, 2021. https://doi.org/10.7554/eLife.75639.
B. G. Godard, R. Dumollard, C.-P. J. Heisenberg, and A. Mcdougall, “Combined effect of cell geometry and polarity domains determines the orientation of unequal division,” eLife, vol. 10. eLife Sciences Publications, 2021.
Godard BG, Dumollard R, Heisenberg C-PJ, Mcdougall A. 2021. Combined effect of cell geometry and polarity domains determines the orientation of unequal division. eLife. 10, e75639.
Godard, Benoit G., et al. “Combined Effect of Cell Geometry and Polarity Domains Determines the Orientation of Unequal Division.” ELife, vol. 10, e75639, eLife Sciences Publications, 2021, doi:10.7554/eLife.75639.
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