Fig. 2

Developmental mechanisms, initial and final morphology. a Example of an initial morphology. Cylinders represent epithelial cells. Cells in yellow express a gene that is not expressed in the cells in blue. All blue cells express the same genes. b Example of a developmental mechanism. Balls represent gene products. Red balls are extracellular diffusive gene products (a signal). Gene 2 is the gene expressed by the cells in yellow in a. For simplicity the signal transduction pathway is not represented. Green arrows represent positive regulation. Red cells represent negative regulation. Squares represent cell behaviors or cell mechanical properties. c Three examples of final morphologies arising from the initial morphology in a through the developmental mechanism in b (according to a mathematical general model of development called EmbryoMaker [45]). The morphological variation is the one arising from variation in the amount of signal being secreted (the signal is gene 1). The variation is mostly in the overall curvature of the epithelium. There is a default cell division rate in all cells. As in a cylinders represent epithelial cells, color represents z-axis coordinate values as in a topographic map. d. As in c but for the three final morphologies arising from variation in the diffusivity of the signal. The morphologies vary in how the curvature decreases with the distance to the signal’s source. In the morphology in the upper row the curvature is very strong near the cells secreting the signal. In the morphology in the lower row, the curvature is more evenly distributed (low row) (e) as in a. f As in b but for a different developmental mechanism. The gene that yellow cells in d express is gene 2. g Three examples of final morphologies arising from the initial morphology in d through the developmental mechanism in e (also according to EmbryoMaker)