Response of epithelial cell and tissue shape to external forces in vivo

Abstract

How actomyosin generates forces at epithelial adherens junctions has been extensively studied. However, less is known about how a balance between internal and external forces establishes epithelial cell, tissue and organ shape. We used the Drosophila egg chamber to investigate how contractility at adherens junctions in the follicle epithelium is modulated to accommodate and resist forces arising from the growing germ line. We found that between stages 6 and 9, adherens junction tension in the postmitotic epithelium decreases, suggesting that the junctional network relaxes to accommodate germline growth. At that time, a prominent medial Myosin II network coupled to corrugating adherens junctions develops. Local enrichment of medial Myosin II in main body follicle cells resists germline-derived forces, thus constraining apical areas and, consequently, cuboidal cell shapes at stage 9. At the tissue and organ level, local reinforcement of medial junction architecture ensures the timely contact of main body cells with the expanding oocyte and imposes circumferential constraints on the germ line guiding egg elongation. Our study provides insight into how adherens junction tension promotes cell and tissue shape transitions while integrating the growth and shape of an internally enclosed structure in vivo.

Transient opening of tricellular vertices controls paracellular transport through the follicle epithelium duringDrosophilaoogenesis

“…7A,D), suggesting that cortical tension in FCs is decreasing during this interval. This notion was consistent with decreasing levels of the tension-sensitive protein vinculin (vinculin-GFP; Maartens et al, 2016) at FC junctions from stage 6 to stage 9 (data not shown) and with direct measurements of cortical tension by laser ablation experiments (Balaji et al, 2019). We hypothesized that a decrease in cortical tension could play a role in initiating patency.…”

Transient opening of tricellular vertices controls paracellular transport through the follicle epithelium during Drosophila oogenesis

“…7K-L). This was associated with a conspicuous change in the morphology of AJs, which were straight in control FCs, but corrugated in MLCK-expressing FCs (Fig 7K',L'), suggesting that MLCK-induced myosin contractility led to an increase in cortical tension, consistent with the findings of (Balaji et al, 2019). Strikingly, FCs in MLCK-expressing follicles failed to round up and instead maintained their hexagonal shape at stage 10A, and showed a strong reduction in the size of intercellular openings (Fig.…”

“…7A,D), suggesting that cortical tension in FCs is decreasing during this interval. This notion was consistent with decreasing levels of the tension-sensitive protein vinculin (vinculin-GFP; Maartens et al, 2016) at FC junctions from stage 6 to stage 9 (data not shown) and with direct measurements of cortical tension by laser ablation experiments (Balaji et al, 2019). We hypothesized that a decrease in cortical tension could play a role in initiating patency.…”

A release-and-capture mechanism generates an essential non-centrosomal microtubule array during tube budding

“…Furthermore, cell apices in ncd::γ-tubulin-EGFP placodes often showed a convoluted apical junctional morphology ('wavy' junctions; Fig. 4a-e), that is indicative of strong, possibly excessive, apical constriction 31,32 . In line with this finding, cells showed more constricted apices compared to control (Fig.…”