MoD Special Issue on the roles of physical forces in animal development

D’Arcy Thompson, in his famous book “On Growth and Form” published a hundred years ago, set out to explain the ‘physical considerations’ underlying the form of living things (Thompson, D.W., 1917, On Growth and Form, University Press, Cambridge). He realized that biological processes abide physical laws, yet these laws until today remain largely unknown. The advent of molecular biology had diverted the interest of developmental biologists away from the physical principles towards the analysis of genes and proteins in embryos. As a result, the past decades havewitnessed a tremendous advancement in our understanding of the genetic control of animal and plant development. The recent years, however, have seen a renewed interest in ‘developmental mechanics’ the role ofmechanical properties and physical forces in animal development. Enabled by latest advances inmicroscopy techniques, the ability tomeasure andmanipulate physical forces in embryos, and computational approaches, biologists, in close collaboration with physicist, mathematicians and computer scientists, have begun nowadays to explore the physical principles of animal development. This Special Issue on ‘Roles of physical forces in animal development’ covers in ten reviews some of the current research areas where the analysis of physical forces has contributed to our understanding of developmental processes. As we know today, the control of size and shape of embryos requires the spatiotemporal coordination of mechanical processes, including the shaping, division, migration, positioning and apoptosis of cells. These processes to a large extent depend on the cell’s cytoskeleton, but also on its adhesive contacts with neighboring cells and the extracellular matrix. In particular, the molecular interaction of motor proteins with actin filaments generates forces that can lead to cellular constrictions that, if coordinated, can give rise at a larger scale to tissue deformations including elongation, furrowing or folding. In addition to the activity, the organization of the cytoskeleton itself can be coordinated among cells, giving rise to supra-cellular structures like actomyosin cables that can generate tensile forces. Forces not only influence the cells