Pierre Haas (Max Planck Institutes for the Physics of Complex Systems and of Molecular Cell Biology and Genetics, Center for Systems Biology Dresden)
The formation of complex tissues during development relies on robust spatiotemporal coordination of mechanical forces between different tissues or in complex geometries. In this talk, I will present two examples of this interplay of tissues and forces.
I will first show how inter-tissue forces underpin the first folding event in the developing zebrafish forebrain . I will develop a minimal fluid mechanical model of tissue flows during zebrafish gastrulation to identify the minimal set of spatiotemporally varying force singularities required and sufficient to reproduce the observed tissue flows qualitatively and quantitatively, respectively. I will then discuss how we have tested these predictions in vitro, highlighting how our combined experimental and theoretical results show how the coordination of different mechanical processes in different tissues is required for correct folding of the zebrafish forebrain.
I will then reveal the mechanics of out-of-plane forces in the curved tissue geometry of the so-called inversion process during which a programme of cell shape changes turns the embryos of the green alga Volvox inside out . I will develop an elastic model to quantify the intrinsic, preferred curvature of the tissue from its out-of-plane recoil observed in laser ablation experiments. Surprisingly, our model shows how even small intrinsic curvature changes and hence cell shape changes contribute mechanically to the shape of the folding tissue.
 A. Inman, J. E. Lutton, E. Spiritosanto, M. Tada, T. Bretschneider, P. A. Haas, and M. Smutny, biorxiv:2023.06.21.545965v1 (2023)
 P. A. Haas and S. M. H. Höhn, preprint (2023)