title: Spindle position in symmetric cell divisions during epiboly is controlled by opposing and dynamic apicobasal forces.
abstract: Orientation of cell division is a vital aspect of tissue morphogenesis and growth. Asymmetric divisions generate cell fate diversity and epithelial stratification, whereas symmetric divisions contribute to tissue growth, spreading, and elongation. Here, we describe a mechanism for positioning the spindle in symmetric cell divisions of an embryonic epithelium. We show that during the early stages of epiboly, spindles in the epithelium display dynamic behavior within the plane of the epithelium but are kept firmly within this plane to give a symmetric division. This dynamic stability relies on balancing counteracting forces: an apically directed force exerted by F-actin/myosin-2 via active cortical flow and a basally directed force mediated by microtubules and myosin-10. When both forces are disrupted, spindle orientation deviates from the epithelial plane, and epithelial surface is reduced. We propose that this dynamic mechanism maintains symmetric divisions while allowing the quick adjustment of division plane to facilitate even tissue spreading.
authors.affiliation: Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK. sarah.woolner@manchester.ac.uk
authors.forename: Sarah
authors.initials: S
authors.lastname: Woolner
authors.forename: Nancy
authors.initials: N
authors.lastname: Papalopulu
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002450:Cell Communication; D002454:Cell Differentiation; D002455:Cell Division; D016764:Cell Polarity; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005260:Female; D005455:Fluorescent Antibody Technique; D008870:Microtubules / Q000378:metabolism; D009024:Morphogenesis / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D008941:Spindle Apparatus / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology*
chemical_list: D000199:Actins; D009218:Myosins