Anonymous sources: where do adult β cells come from?

Evidence that the pool of insulin-producing β cells in the pancreas is reduced in both major forms of diabetes mellitus has led to efforts to understand β cell turnover in the adult pancreas. Unfortunately, previous studies have reached opposing conclusions regarding the source of new β cells during regeneration in the adult pancreas. In this issue of the JCI, Xiao et al. use a novel mouse model for detecting new β cells derived from non-β cells to demonstrate the absence of β cell neogenesis from non-β cells during normal postnatal growth and in models of β cell regeneration. This work adds to mounting evidence that in most physiological and pathological conditions, β cell neogenesis may not make large contributions to the postnatal β cell pool - at least not in rodents.