Mechanochemical modelling of dorsal closure reveals emergent cell behaviour in tissue morphogenesis

Tissue morphogenesis integrates cell type-specific biochemistry and architecture, cellular force generation and mechanisms coordinating forces amongst neighbouring cells and tissues. We use finite element-based modelling to explore the interconnections at these multiple biological scales in embryonic dorsal closure, where pulsed actomyosin contractility in adjacent Amnioserosa (AS) cells powers the closure of an epidermis opening. Based on our in vivo observations, the model implements F-actin nucleation periodicity that is independent of MyoII activity. Our model reveals conditions, where depleting MyoII activity nevertheless indirectly affects oscillatory F-actin behaviour, without the need for biochemical feedback. In addition, it questions the previously proposed role of Dpp-mediated regulation of the patterned actomyosin dynamics in the AS tissue, suggesting them to be emergent. Tissue-specific Dpp interference supports the models prediction. The model further predicts that the mechanical properties of the surrounding epidermis tissue feed back on the shaping and patterning of the AS tissue. Finally, our models parameter space reproduces mutant phenotypes and provides predictions for their underlying cause. Our modelling approach thus reveals several unappreciated mechanistic properties of tissue morphogenesis.