Pax6 is a transcription factor that is both necessary and sufficient for eye development in a number of animal species. Precisely how Pax6 achieves this feat, helping to build eye structures that are morphologically and phylogenetically distinct, is unclear. Now, Timothy Grocott and colleagues propose that Pax6, together with the morphogen encoding genes transforming growth factor-beta 2 (Tgfb2) and follistatin (Fst), forms a self-organising Turing network that patterns the developing eye. Using the chick as a model system, they first show that extrinsic Bmp signals drive Pax6 expression in the distal end of the optic vesicle. Pax6, in turn, induces the expression of Tgfb2 and its antagonist Fst in this region. Following on from this, the researchers use computer simulations to examine a reaction-diffusion model of the interactions between Pax6, Tgfb2 and Fst. Their modelling reveals that these factors can form a self-organising, activator-inhibitor Turing network that can polarise the optic vesicle along its proximal-distal axis. Moreover, the authors report that, while positional information provided by a Shh gradient can also contribute to pattern formation, the Pax6/Tgfb2/Fst network is sufficient to trigger self-organisation. Together, these findings provide insights into how self-organisation can be initiated independently of tissue interactions, for instance in organoid cultures.
