title: A soft cortex is essential for asymmetric spindle positioning in mouse oocytes.
abstract: At mitosis onset, cortical tension increases and cells round up, ensuring correct spindle morphogenesis and orientation. Thus, cortical tension sets up the geometric requirements of cell division. On the contrary, cortical tension decreases during meiotic divisions in mouse oocytes, a puzzling observation because oocytes are round cells, stable in shape, that actively position their spindles. We investigated the pathway leading to reduction in cortical tension and its significance for spindle positioning. We document a previously uncharacterized Arp2/3-dependent thickening of the cortical F-actin essential for first meiotic spindle migration to the cortex. Using micropipette aspiration, we show that cortical tension decreases during meiosis I, resulting from myosin-II exclusion from the cortex, and that cortical F-actin thickening promotes cortical plasticity. These events soften and relax the cortex. They are triggered by the Mos-MAPK pathway and coordinated temporally. Artificial cortex stiffening and theoretical modelling demonstrate that a soft cortex is essential for meiotic spindle positioning.
authors.affiliation: 1] CIRB, Collège de France, and CNRS-UMR7241 and INSERM-U1050, Equipe Labellisée Ligue Contre le Cancer, Paris F-75005, France.
authors.forename: Agathe
authors.initials: A
authors.lastname: Chaigne
authors.forename: Clément
authors.initials: C
authors.lastname: Campillo
authors.forename: Nir S
authors.initials: NS
authors.lastname: Gov
authors.forename: Raphaël
authors.initials: R
authors.lastname: Voituriez
authors.forename: Jessica
authors.initials: J
authors.lastname: Azoury
authors.forename: Claudia
authors.initials: C
authors.lastname: Umaña-Diaz
authors.forename: Maria
authors.initials: M
authors.lastname: Almonacid
authors.forename: Isabelle
authors.initials: I
authors.lastname: Queguiner
authors.forename: Pierre
authors.initials: P
authors.lastname: Nassoy
authors.forename: Cécile
authors.initials: C
authors.lastname: Sykes
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Verlhac
authors.forename: Marie-Emilie
authors.initials: ME
authors.lastname: Terret
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000818:Animals; D005260:Female; D008540:Meiosis / Q000502:physiology*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D008954:Models, Biological; D009218:Myosins / Q000378:metabolism; D017232:Oncogene Proteins v-mos / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism*; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000502:physiology*
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D017232:Oncogene Proteins v-mos; D020929:Mitogen-Activated Protein Kinase Kinases; D009218:Myosins