title: Cellular mechanics of germ band retraction in Drosophila.
abstract: Germ band retraction involves a dramatic rearrangement of the tissues on the surface of the Drosophila embryo. As germ band retraction commences, one tissue, the germ band, wraps around another, the amnioserosa. Through retraction the two tissues move cohesively as the highly elongated cells of the amnioserosa contract and the germ band moves so it is only on one side of the embryo. To understand the mechanical drivers of this process, we designed a series of laser ablations that suggest a mechanical role for the amnioserosa. First, we find that during mid retraction, segments in the curve of the germ band are under anisotropic tension. The largest tensions are in the direction in which the amnioserosa contracts. Second, ablating one lateral flank of the amnioserosa reduces the observed force anisotropy and leads to retraction failures. The other intact flank of amnioserosa is insufficient to drive retraction, but can support some germ band cell elongation and is thus not a full phenocopy of ush mutants. Another ablation-induced failure in retraction can phenocopy mys mutants, and does so by targeting amnioserosa cells in the same region where the mutant fails to adhere to the germ band. We conclude that the amnioserosa must play a key, but assistive, mechanical role that aids uncurling of the germ band.
authors.affiliation: Department of Physics & Astronomy, VU Station B 351807, Vanderbilt University, Nashville, TN, USA.
authors.forename: Holley E
authors.initials: HE
authors.lastname: Lynch
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Crews
authors.forename: Brett
authors.initials: B
authors.lastname: Rosenthal
authors.forename: Elliott
authors.initials: E
authors.lastname: Kim
authors.forename: Robert
authors.initials: R
authors.lastname: Gish
authors.forename: Karl
authors.initials: K
authors.lastname: Echiverri
authors.forename: M Shane
authors.initials: MS
authors.lastname: Hutson
mesh_terms: D000818:Animals; D019521:Body Patterning; D004330:Drosophila / Q000196:embryology*; D008856:Microscopy, Fluorescence
keywords: Amnioserosa; Autonomous cell elongation; Cellular mechanics; Embryogenesis; Germ band retraction; Laser microsurgery