title: F-actin mechanics control spindle centring in the mouse zygote.
abstract: Mitotic spindle position relies on interactions between astral microtubules nucleated by centrosomes and a rigid cortex. Some cells, such as mouse oocytes, do not possess centrosomes and astral microtubules. These cells rely only on actin and on a soft cortex to position their spindle off-centre and undergo asymmetric divisions. While the first mouse embryonic division also occurs in the absence of centrosomes, it is symmetric and not much is known on how the spindle is positioned at the exact cell centre. Using interdisciplinary approaches, we demonstrate that zygotic spindle positioning follows a three-step process: (1) coarse centring of pronuclei relying on the dynamics of an F-actin/Myosin-Vb meshwork; (2) fine centring of the metaphase plate depending on a high cortical tension; (3) passive maintenance at the cell centre. Altogether, we show that F-actin-dependent mechanics operate the switch between asymmetric to symmetric division required at the oocyte to embryo transition.
authors.affiliation: CIRB, Collège de France, and CNRS-UMR7241 and INSERM-U1050, Equipe labellisée Ligue contre le Cancer, Paris F-75005, France.
authors.forename: Agathe
authors.identifier: http://orcid.org/0000-0003-3893-8312
authors.initials: A
authors.lastname: Chaigne
authors.affiliation: Université Evry Val d'Essonne, LAMBE, Boulevard F Mitterrand, Evry 91025, France.
authors.forename: Clément
authors.initials: C
authors.lastname: Campillo
authors.affiliation: UMR7600-CNRS/UPMC, 4 Place Jussieu, Paris F-75005, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Voituriez
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Nir S
authors.initials: NS
authors.lastname: Gov
authors.affiliation: CNRS-UMR168, Paris F-75248, France.|UPMC, 4 Place Jussieu, Paris F-75248, France.|Institut Curie, Centre de Recherche, Laboratoire Physico-Chimie, Paris F-75248, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Sykes
authors.affiliation: CIRB, Collège de France, and CNRS-UMR7241 and INSERM-U1050, Equipe labellisée Ligue contre le Cancer, Paris F-75005, France.
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Verlhac
authors.affiliation: CIRB, Collège de France, and CNRS-UMR7241 and INSERM-U1050, Equipe labellisée Ligue contre le Cancer, Paris F-75005, France.
authors.forename: Marie-Emilie
authors.initials: ME
authors.lastname: Terret
mesh_terms: D000199:Actins / Q000502:physiology*; D000818:Animals; D005307:Fertilization in Vitro; D008297:Male; D051379:Mice; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D013094:Spermatozoa / Q000166:cytology / Q000502:physiology; D008941:Spindle Apparatus / Q000502:physiology*
chemical_list: D000199:Actins