Abstract:Cell fates are often determined by the morphology and the composition of their immediate environment. In turn, cells modify their environment and through this feedback complex patterns emerge where cells are maintained at right places and right proportions. We now rapidly gain knowledge on how biochemical signals drive cell decisions, however, we lack understanding in how changes at the level of a cell lead to macroscopic changes in morphology. We propose that the emergence of complex morphologies and cell fate decisions can be reduced to a few simple rules, where changes in cell’s polarity and state depend only on neighbor cells. With the help of mathematical approaches, we conceptualize current knowledge on biochemical and biomechanical cell-cell interactions and show that these can successfully capture first 4.5 days of blastocyst development. When applied to cell polarities, this approach can recapitulate the transition from sphere to branched organoids, main stages of sea urchin gastrulation and budding and wrapping sheet-to-tube transitions in tubulogenesis. We will discuss possible applications of these approaches to intestinal organoids and the emergence of vascular networks.