title: The beetle amnion and serosa functionally interact as apposed epithelia.
abstract: Unlike passive rupture of the human chorioamnion at birth, the insect extraembryonic (EE) tissues - the amnion and serosa - actively rupture and withdraw in late embryogenesis. Withdrawal is essential for development and has been a morphogenetic puzzle. Here, we use new fluorescent transgenic lines in the beetle Tribolium castaneum to show that the EE tissues dynamically form a basal-basal epithelial bilayer, contradicting the previous hypothesis of EE intercalation. We find that the EE tissues repeatedly detach and reattach throughout development and have distinct roles. Quantitative live imaging analyses show that the amnion initiates EE rupture in a specialized anterior-ventral cap. RNAi phenotypes demonstrate that the serosa contracts autonomously. Thus, apposition in a bilayer enables the amnion as 'initiator' to coordinate with the serosa as 'driver' to achieve withdrawal. This EE strategy may reflect evolutionary changes within the holometabolous insects and serves as a model to study interactions between developing epithelia.
authors.affiliation: Institute for Developmental Biology, University of Cologne, Cologne, Germany.
authors.forename: Maarten
authors.initials: M
authors.lastname: Hilbrant
authors.affiliation: Institute for Developmental Biology, University of Cologne, Cologne, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Horn
authors.affiliation: Institute for Developmental Biology, University of Cologne, Cologne, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Koelzer
authors.affiliation: Institute for Developmental Biology, University of Cologne, Cologne, Germany.
authors.forename: Kristen A
authors.identifier: http://orcid.org/0000-0002-6417-251X
authors.initials: KA
authors.lastname: Panfilio
mesh_terms: D000818:Animals; D004848:Epithelium / Q000502:physiology; D005321:Extraembryonic Membranes / Q000502:physiology*; D061848:Optical Imaging; D012098:Reproduction; D012704:Serous Membrane / Q000502:physiology; D014231:Tribolium / Q000502:physiology*
keywords: RNA interference (RNAi); cell biology; developmental biology; epithelial morphogenesis; extraembryonic development; fluorescent live imaging; insects; light sheet microscopy; stem cells
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