A δ-cell subpopulation with a pro-β-cell identity confers efficient age-independent recovery in a zebrafish model of diabetes

Restoring damaged {beta}-cells in diabetic patients by harnessing the plasticity of other pancreatic cells raises the questions of the efficiency of the process and of the functionality of the new Insulin-expressing cells. To overcome the weak regenerative capacity of mammals, we used regeneration-prone zebrafish to study {beta}-cells arising following destruction. We show that most new insulin cells differ from the original {beta}-cells as they are Somatostatin+ Insulin+, but are nevertheless functional and normalize glycemia. These bihormonal cells are transcriptionally close to a subset of {delta}-cells in normal islets characterized by the expression of somatostatin 1.1 (sst1.1), the {beta}-cell genes pdx1, slc2a2 and gck, and the machinery for glucose-induced Insulin secretion. {beta}-cell destruction triggers massive sst1.1 {delta}-cell conversion to bihormonal cells. Our work shows that their pro- {beta}-cell identity predisposes this zebrafish {delta}-cell subpopulation to efficient age-independent neogenesis of Insulin-producing cells and provides clues to restoring functional {beta}-cells in mammalian diabetes models.