Mechanics of epithelial tissue formation

Abstract

A key process in the life of any multicellular organism is its development from a single egg into a full grown adult. The first step in this process often consists of forming a tissue layer out of randomly placed cells on the surface of the egg. We present a model for generating such a tissue, based on mechanical interactions between the cells, and find that the resulting cellular pattern corresponds to the Voronoi tessellation of the nuclei of the cells. Experimentally, we obtain the same result in both fruit flies and flour beetles, with a distribution of cell shapes that matches that of the model, without any adjustable parameters. Finally, we show that this pattern is broken when the cells grow at different rates.

Regionalized tissue fluidization is required for epithelial gap closure during insect gastrulation

“…1e). In order to examine the expansion at the cellular level, we imaged embryos expressing LifeAct-eGFP that labels cortical F-actin 13,16 and segmented the apical surface of all serosal cells at the five reference stages (Fig. 1b) during serosa expansion ( Fig.…”

“…All mRNA injections were performed into embryos of the vermilion white strain. The following transgenic lines were used for live imaging: (i) EFA-nGFP, ubiquitously expressing a nuclear-localized GFP reporter 41 (kindly provided by Michalis Averof's laboratory); (ii) αTub-H2A-eGFP, ubiquitously expressing a nuclear eGFP reporter (kindly provided by Peter Kitzmann from Gregor Bucher's laboratory); (iii) EFA-Gap43-YFP-2A-Histone-RFP, ubiquitously expressing both a membrane YFP and a nuclear RFP reporter (kindly provided by Johannes Schinko and Anna Gilles from Michalis Averof's laboratory); (iv) αTub-LifeAct-eGFP, ubiquitously labeling filamentous actin with eGFP 16 (kindly provided by the Van der Zee laboratory); and (v) αTub-Tc-sqh-eGFP, ubiquitously labeling the Tribolium non-muscle myosin II through its regulatory light chain. The predicted Tribolium spaghetti squash gene (Tc-sqh) encoding the non-muscle myosin II regulatory light chain was identified by BLAST analysis against the Tribolium genome 42 and shares 93% similarity with the Drosophila melanogaster sqh gene.…”

“…Injected eggs were incubated in humid chambers at 30°C for~2 h and the most homogeneously labeled and bright embryos were selected for imaging. For parental knock-down of Tc-zen1 by RNAi, dsRNA was injected into the abdomen of female pupae collected from the αTub-LifeAct-eGFP transgenic line 16 . Injected adult females were crossed to males from the same line and their eggs were collected for imaging.…”

Fog signaling has diverse roles in epithelial morphogenesis in insects

“…Tribolium castaneum strains: San Bernandino wildtype (Brown et al, 2009), nuclear GFP (nGFP) (Sarrazin et al, 2012), LifeAct-GFP (van Drongelen et al, 2018) were cultured as described (Brown et al, 2009). Oncopeltus fasciatus was cultured as described (Ewen-Campen et al, 2011).…”

“…For live imaging of the posterior poles, eggs were propped up vertically (resting against another egg for stability) on a glass-bottomed Petri dish (MatTek) with their posterior against the glass. Live imaging transgenic nuclear GFP (nGFP) (Sarrazin et al, 2012) or LifeAct-GFP (van Drongelen et al, 2018) embryos was done at room temperature using the Zeiss AxioImager.Z2 in combination with an Apotome.2 and movable stage (Zen2 Blue).…”