Marie Emilie Terret (CIRB, Collège de France, Paris). Biophysics seminar ENS-ESPCI.

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6 October 2017 13:00 » 14:00 — Amphi Schützenberger , ESPCI Paris

Cortical tension participates in chromosome alignment in mouse oocytes.

In oocytes, cells lacking canonical centrosomes, two F-actin networks replace astral microtubules for spindle positioning. They exert forces on the spindle sufficient to embark it to the cortex, leading to an asymmetric division in size. The first actin mesh is cytoplasmic and includes an actin cage surrounding the meiotic spindle. The second one consists of a cortical actin thickening that promotes a decrease in cortical tension and cortex softening. We have shown previously that this change in cortex mechanics controls the geometry of oocyte (and embryo) division since oocytes presenting too stiff or too soft cortices divide symmetrically (1-3). Interestingly, human and mouse oocytes developmental potential is accurately predicted by their cortical tension within hours after fertilization: if they are too stiff or too soft, embryos will cease development (4). Our goal is to understand the origin of early developmental failure due to cortical tension defects. Our results point towards a role of cortical tension in chromosome alignment in mouse oocytes. We show that aberrant cortical tension, a frequent defect in a normal population, could lead to chromosome alignment defects in oocytes, potentially contributing to oocyte predisposition to chromosome segregation defects, a leading cause of aneuploidy in embryos.

1. Chaigne A et al. A soft cortex is essential for asymmetric spindle positioning in mouse oocytes. Nat Cell Biol 15 : 958-66 (2013).
2. Chaigne A et al. A narrow window of cortical tension guides asymmetric spindle positioning in the mouse oocyte. Nat Commun 6, 6027 (2015).
3. Chaigne A et al. F-Actin Mechanics Control Spindle Centring In The Mouse Zygote. Nat Commun 7,10253 (2016).
4. Yanez LZ et al. Human oocyte developmental potential is predicted by mechanical properties within hours after fertilization. Nat Commun 7, 10809 (2016).

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