title: Sequential contraction and exchange of apical junctions drives zippering and neural tube closure in a simple chordate.
abstract: Unidirectional zippering is a key step in neural tube closure that remains poorly understood. Here, we combine experimental and computational approaches to identify the mechanism for zippering in a basal chordate, Ciona intestinalis. We show that myosin II is activated sequentially from posterior to anterior along the neural/epidermal (Ne/Epi) boundary just ahead of the advancing zipper. This promotes rapid shortening of Ne/Epi junctions, driving the zipper forward and drawing the neural folds together. Cell contact rearrangements (Ne/Epi + Ne/Epi → Ne/Ne + Epi/Epi) just behind the zipper lower tissue resistance to zipper progression by allowing transiently stretched cells to detach and relax toward isodiametric shapes. Computer simulations show that measured differences in junction tension, timing of primary contractions, and delay before cell detachment are sufficient to explain the speed and direction of zipper progression and highlight key advantages of a sequential contraction mechanism for robust efficient zippering.
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Hashimoto
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA; Committee on Development, Regeneration and Stem Cell Biology, University of Chicago, Chicago, IL 60637, USA. Electronic address: robin@crans.org.
authors.forename: Francois B
authors.initials: FB
authors.lastname: Robin
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Sherrard
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA; Committee on Development, Regeneration and Stem Cell Biology, University of Chicago, Chicago, IL 60637, USA; Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA. Electronic address: emunro@uchicago.edu.
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Munro
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology; D043344:Chordata; D002938:Ciona intestinalis / Q000378:metabolism; D007365:Intercellular Junctions / Q000378:metabolism / Q000473:pathology*; D009432:Neural Crest / Q000166:cytology*; D054259:Neural Tube / Q000166:cytology*