Drosophilaaxis extension is robust to an orthogonal pull by invaginating mesoderm

Abstract

As tissues grow and change shape during animal development, they physically pull and push on each other and these mechanical interactions can be important for morphogenesis. During Drosophila gastrulation, mesoderm invagination temporally overlaps with the extension of the ectodermal germband; the latter is caused primarily by Myosin II-driven polarised cell intercalation. Here we investigate the impact of mesoderm invagination on ectoderm extension, examining possible mechanical and mechanotransductive effects on Myosin II recruitment and polarised cell intercalation. We find that the germband ectoderm is deformed by the mesoderm pulling in the orthogonal direction, showing mechanical coupling between these tissues. However, we do not find a significant change in Myosin II planar polarisation in response to mesoderm invagination, nor an effect on the rate of junction shrinkage leading to cell intercalation events. We find some impact on the orientation of neighbour exchange events, and an increased rate of growth of new cell junctions, but this makes little difference to the rate of cell intercalation. We conclude that the cellular mechanisms of axis extension are robust to the mechanical pull of mesoderm invagination.

Signatures of structural disorder in developing epithelial tissues

“…It has recently been proposed that the stretch from ventral furrow invagination recruits myosin to cell junctions in the germband in a planar polarized fashion via mechanical feedback mechanisms, which then promote tissue flow [18]. However, other studies have shown that myosin planar polarity acts downstream of AP patterning systems [6,7,21] and have shown that the germband displays cell rearrangements and tissue elongation even when the ventral furrow is disrupted [10,13,44,45]. Here, we find delays in disorder, cell rearrangement, and tissue elongation in sna twi mutant embryos, suggesting that the ventral furrow facilitates but is not required for tissue remodeling.…”