PT  - JOURNAL ARTICLE
AU  - Natalie A. Dye
AU  - Marko Popović
AU  - Stephanie Spannl
AU  - Raphaël Etournay
AU  - Dagmar Kainmüller
AU  - Eugene W. Myers
AU  - Frank Jülicher
AU  - Suzanne Eaton
TI  - Cell dynamics underlying oriented growth of the <em>Drosophila</em> wing imaginal disc
AID  - 10.1101/140038
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 140038
4099  - http://biorxiv.org/content/early/2017/05/19/140038.short
4100  - http://biorxiv.org/content/early/2017/05/19/140038.full
AB  - Quantitative analysis of the dynamic cellular mechanisms shaping the Drosophila wing during its larval growth phase has been limited, impeding our ability to understand how morphogen patterns regulate tissue shape. Such analysis requires imaging explants 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 in vivo 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 directly observe growth and apply recently developed methods for quantitatively decomposing tissue shape changes into cellular contributions. We discover that while 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.