title: Mechanical state, material properties and continuous description of an epithelial tissue.
abstract: During development, epithelial tissues undergo extensive morphogenesis based on coordinated changes of cell shape and position over time. Continuum mechanics describes tissue mechanical state and shape changes in terms of strain and stress. It accounts for individual cell properties using only a few spatially averaged material parameters. To determine the mechanical state and parameters in the Drosophila pupa dorsal thorax epithelium, we severed in vivo the adherens junctions around a disc-shaped domain comprising typically a hundred cells. This enabled a direct measurement of the strain along different orientations at once. The amplitude and the anisotropy of the strain increased during development. We also measured the stress-to-viscosity ratio and similarly found an increase in amplitude and anisotropy. The relaxation time was of the order of 10 s. We propose a space-time, continuous model of the relaxation. Good agreement with experimental data validates the description of the epithelial domain as a continuous, linear, visco-elastic material. We discuss the relevant time and length scales. Another material parameter, the ratio of external friction to internal viscosity, is estimated by fitting the initial velocity profile. Together, our results contribute to quantify forces and displacements, and their time evolution, during morphogenesis.
authors.affiliation: Genetics and Developmental Biology, Team Polarity, division and morphogenesis, Institut Curie, UMR3215 CNRS, U934 Inserm, 26 rue d'Ulm, F-75248 Paris Cedex 05, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bonnet
authors.forename: Philippe
authors.initials: P
authors.lastname: Marcq
authors.forename: Floris
authors.initials: F
authors.lastname: Bosveld
authors.forename: Luc
authors.initials: L
authors.lastname: Fetler
authors.forename: Yohanns
authors.initials: Y
authors.lastname: Bellaïche
authors.forename: François
authors.initials: F
authors.lastname: Graner
mesh_terms: D022005:Adherens Junctions / Q000502:physiology*; D000818:Animals; D016880:Anisotropy; D004331:Drosophila melanogaster; D004848:Epithelium / Q000502:physiology* / Q000648:ultrastructure; D008954:Models, Biological; D009024:Morphogenesis / Q000502:physiology*; D013314:Stress, Mechanical; D013909:Thorax / Q000502:physiology* / Q000648:ultrastructure; D014783:Viscosity