  Recent 3D organ reconstitution studies show that a group of stem cells can
establish a body axis and acquire different fates in a spatially organized
manner. How such symmetry breaking happens in the absence of external spatial
cues, and how developmental circuits are built to permit this is largely
unknown. Here, we review spontaneous symmetry breaking phenomena in organoids,
and hypothesize underlying patterning mechanisms that involve interacting
diffusible species. Recent theoretical advances offer new directions beyond the
prototypical Turing model. Experiments guided by theory will allow us to
predict and control organoid self-organization.
