Résumé
Embryonic boundaries are sharp delimitations that prevent intermingling between different cell populations. They are essential for the development of well-organized structures and ultimately a functional organism. It has been long believed that this process was driven by global differences in cell adhesion strength, or expression of different types of adhesion molecules. The actual picture turns out to be quite different: Boundaries should be viewed as abrupt discontinuities, where cortical contractility is acutely upregulated in response to specific cell surface contact receptors which act as repulsive cues. Cell adhesion is also modulated along the interface, in different ways depending on the type of boundary, but in all cases the process is subordinated to the function of the cortical actomyosin cytoskeleton.