Summary The notochord is an evolutionary novelty in vertebrates that functions as an important signaling center during development. Notochord ablation in chicken has demonstrated that it is crucial for pancreas development; however, the molecular mechanism has not been fully described. Here, we show that in zebrafish, the loss of function of nog2, a Bmp antagonist expressed in the notochord, impairs β cell differentiation, compatible with the antagonistic role of Bmp in β cell differentiation. In addition, we show that nog2 expression in the notochord is induced by at least one notochord enhancer and its loss of function reduces the number of pancreatic progenitors and impairs β cell differentiation. Tracing Nog2 diffusion, we show that Nog2 emanates from the notochord to the pancreas progenitor domain. Finally, we find a notochord enhancer in human and mice Nog genomic landscapes, suggesting that the acquisition of a Nog notochord enhancer occurred early in the vertebrate phylogeny and contributes to the development of complex organs like the pancreas.

In multicellular organisms, cis-regulation controls gene expression in space and time. Despite the essential implication of cis-regulation in the development and evolution of organisms and in human diseases, our knowledge about regulatory sequences largely derives from analyzing their activity individually and outside their genomic context. Indeed, the contribution of these sequences to the expression of their target genes in their genomic context is still largely unknown. Here we present a novel genetic screen designed to visualize and interrupt gene regulatory landscapes in vertebrates. In this screen, based on the random insertion of an engineered Tol2 transposon carrying a strong insulator separating two fluorescent reporter genes, we isolated hundreds of zebrafish lines containing insertions that disrupt the cis-regulation of tissue-specific expressed genes. We therefore provide a new easy-to-handle tool that will help to disrupt and chart the regulatory activity spread through the vast noncoding regions of the vertebrate genome.