An adhesion code ensures robust pattern formation during tissue morphogenesis

An outstanding question in embryo development is how spatial patterns are formed robustly. In the zebrafish spinal cord, neural progenitors form stereotypic stripe-like patterns despite noisy morphogen signaling and large-scale cellular rearrangement required for tissue growth and morphogenesis. We set out to understand the mechanisms underlying this patterning robustness. Our adhesion assays revealed a preference for three neural progenitor types to stabilize contacts with cells of the same type. Genetic analysis uncovered a three-molecule adhesion code, composed of N-cadherin, Cadherin 11, and Protocadherin 19, with unique gene expression profiles for each cell type. Perturbation of the adhesion code results in loss of homotypic preference ex vivo and patterning errors in vivo. Both the cell fate and adhesion code are co-regulated by the common upstream morphogen signal Shh. We propose that robust patterning in tissues undergoing morphogenesis results from a previously unappreciated interplay between morphogen gradient-based patterning and adhesion-based self-organization.