title: Shroom induces apical constriction and is required for hingepoint formation during neural tube closure.
abstract: BACKGROUND
  The morphogenetic events of early vertebrate development generally involve the combined actions of several populations of cells, each engaged in a distinct behavior. Neural tube closure, for instance, involves apicobasal cell heightening, apical constriction at hingepoints, convergent extension of the midline, and pushing by the epidermis. Although a large number of genes are known to be required for neural tube closure, in only a very few cases has the affected cell behavior been identified. For example, neural tube closure requires the actin binding protein Shroom, but the cellular basis of Shroom function and how it influences neural tube closure remain to be elucidated.
  
  
  RESULTS
  We show here that expression of Shroom is sufficient to organize apical constriction in transcriptionally quiescent, naive epithelial cells but not in non-polarized cells. Shroom-induced apical constriction was associated with enrichment of apically localized actin filaments and required the small GTPase Rap1 but not Rho. Endogenous Xenopus shroom was found to be expressed in cells engaged in apical constriction. Consistent with a role for Shroom in organizing apical constriction, disrupting Shroom function resulted in a specific failure of hingepoint formation, defective neuroepithelial sheet-bending, and failure of neural tube closure.
  
  
  CONCLUSIONS
  These data demonstrate that Shroom is an essential regulator of apical constriction during neurulation. The finding that a single protein can initiate this process in epithelial cells establishes that bending of epithelial sheets may be patterned during development by the regulation of expression of single genes.
authors.affiliation: Department of Molecular and Cell Biology, 16 Barker Hall, University of California-Berkeley, Berkeley, CA 94720, USA.
authors.forename: Saori L
authors.initials: SL
authors.lastname: Haigo
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Hildebrand
authors.forename: Richard M
authors.initials: RM
authors.lastname: Harland
authors.forename: John B
authors.initials: JB
authors.lastname: Wallingford
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D019521:Body Patterning; D004625:Embryo, Nonmammalian / Q000196:embryology; D004847:Epithelial Cells; D008840:Microfilament Proteins / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009024:Morphogenesis; D009420:Nervous System / Q000196:embryology*; D009432:Neural Crest / Q000196:embryology* / Q000378:metabolism; D009436:Neural Tube Defects / Q000235:genetics; D014981:Xenopus / Q000196:embryology; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D008840:Microfilament Proteins; D020827:rap1 GTP-Binding Proteins