A simplified mechanism for anisotropic constriction in Drosophila mesoderm.

Understanding how forces and material properties give rise to tissue shapes is a fundamental question in developmental biology. Although Drosophila gastrulation is a major system for investigating tissue morphogenesis, there does not exist a consensus mechanical model that explains all the key features of this process. One key feature of Drosophila gastrulation is its anisotropy - the mesoderm constricts much more along one axis than along the other. Previous explanations have involved graded stress, anisotropic stresses or material properties, or mechanosensitive feedback. Here we show that these mechanisms are not required to explain the anisotropy of constriction. In- stead, constriction can be anisotropic if only two conditions are met: the tissue is elastic, as was demonstrated in our recent study, and the contractile domain is asymmetric. This conclusion is general and does not depend on the values of model parameters. This model can explain classical tissue grafting experiments and more recent laser ablation studies. Furthermore, this model may provide alternative explanations for experiments in other developmental systems, including C. elegans and zebrafish.