Cell dynamics underlying oriented growth of theDrosophilawing imaginal disc

Abstract

Quantitative analysis of the dynamic cellular mechanisms shaping the wing during its larval growth phase has been limited, impeding our ability to understand how morphogen patterns regulate tissue shape. Such analysis requires explants to be imaged under conditions that maintain both growth and patterning, as well as methods to quantify how much cellular behaviors change tissue shape. Here, we demonstrate a key requirement for the steroid hormone 20-hydroxyecdysone (20E) in the maintenance of numerous patterning systems and in explant culture. We find that low concentrations of 20E support prolonged proliferation in explanted wing discs in the absence of insulin, incidentally providing novel insight into the hormonal regulation of imaginal growth. We use 20E-containing media to observe growth directly and to apply recently developed methods for quantitatively decomposing tissue shape changes into cellular contributions. We discover that whereas cell divisions drive tissue expansion along one axis, their contribution to expansion along the orthogonal axis is cancelled by cell rearrangements and cell shape changes. This finding raises the possibility that anisotropic mechanical constraints contribute to growth orientation in the wing disc.

Self-organized patterning of cell morphology via mechanosensitive feedback

“…as described previously (Dye et al, 2017) to make 2D projections of the apical surface, 651 marked by Ecadherin-GFP. This algorithm also outputs a height-map image, in which the 652 value for each pixel corresponds to the level in the Z-stack of the identified apical surface.…”

“…It was suggested that this early growth differential 61 is sufficient to account for the persistence of the cell morphology pattern through the 62 remaining ~40hrs of development. However, it has since been shown that cell 63 rearrangements occur (Dye et al, 2017;Heller et al, 2016), which could relax stress patterns 64 once growth has become uniform. Furthermore, stress patterns may even relax during 65 homogeneous growth in the absence of cell rearrangements (Ranft et al, 2010).…”

“…explanted wing discs using our previously described methods (Dye et al, 2017), starting at 87 96 ℎ AEL and continuing for ~13 ℎ of imaging. We used E-cadherin-GFP as an apical 88 junction marker ( Fig 1A).…”

“…Tiled images were stitched together as Z-stacks; then we obtained the apical surface 672 projection and its corresponding height map as described above and in (Dye et al, 2017). 673 Circular Laser ablation 674 Acquisition:…”

“…We previously published patterns of cellular contributions to anisotropic tissue shear 855 from movies 1-3 (Dye et al, 2017); however here, we calculated these patterns in a more 856 accurate way and report averages over multiple movies (Fig 2A). Previously, we assigned a 857 grid at each timepoint as in (Etournay et al, 2015.…”