A role for Myosin in triggering and executing amnioserosa cell delaminations during dorsal closure

ABSTRACT The remodeling of epithelial tissues is a critical process in morphogenesis, often involving the apoptotic removal of individual cells while preserving tissue integrity. In Drosophila, the amnioserosa—a highly dynamic extra-embryonic tissue—undergoes extensive remodeling, culminating in its complete elimination at the end of dorsal closure. While apoptotic cell delaminations in the amnioserosa have been proposed to contribute to dorsal closure, the cellular mechanisms underlying this process remain poorly understood. In this study, we have investigated actomyosin dynamics during cell delaminations and analyzed the consequences of perturbing non-muscle Myosin activity globally in the entire tissue as well as locally in groups of cells. We found that Myosin plays an essential role in both triggering and executing cell delaminations, with high Myosin contractility promoting cell delamination via caspase activation. Additionally, our results suggest that cell delaminations are governed by both cell-autonomous Myosin dynamics and mechanical cues from the tissue environment. Together, these findings provide new insights into the regulation of epithelial cell removal and the complex interplay between apoptotic and mechanical signals during tissue remodeling. Competing Interest Statement The authors have declared no competing interest. Footnotes After receiving comments from reviewers, several changes were made in the manuscript. Specifically, some panels in Figures 1 and 6 were changed to improve clarity. Quantifications were added as well as the number of cells and embryos analyzed in each experiment. Importantly, experiment presented in Figure 6H was done using a different tool to prevent delaminations. We have now ectopically expressed RHG miRNA (three microRNAs that simultaneously inhibit the proapoptotic genes reaper, hid and grim) in the amnioserosa to prevent cell delaminations. Interestingly, we now found that delaminations are prevented in ECad:GFP; prd-GAL4/UAS-NLS:mCherry, UAS-RHG miRNA; UAS-ctMLCK embryos, in contrast to our previous result using Diap1. We believe this discrepancy arises because the effect of Diap1 is particularly sensitive to its levels of expression, something that has happened in the past in other tissues. Thus, it is possible that in our previous experiment (ECad:GFP; prd-GAL4/UAS-NLS:mCherry, UAS-Diap1,; UAS-ctMLCK embryos, which carry three UAS constructs), Diap1 levels were insufficient to fully block caspase activation and prevent cell delaminations induced by high Myosin phosphorylation. In contrast, the new experiment using UAS-RHG miRNA yields a clear result and effectively prevents the delamination of ctMLCK expressing cells. We can now conclude that the preferential delamination induced by ctMLCK requires caspase activity, and that high MyoII contractility promotes delamination through caspase activation.