Signaling Boundary Conditions Drive Self-Organization of Human "Gastruloids"

Morphogenesis requires tissues to sense and respond to their geometry. In this issue of Developmental Cell, Etoc et al. (2016) show that a confined colony of human embryonic stem cells can spontaneously sense its boundary, generating a self-organized TGF-β signaling gradient that patterns it into a tissue resembling a gastrulating embryo.