Is a β cell a β cell?

PURPOSE OF REVIEW: This report examines recent publications identifying phenotypic and functional heterogeneity among pancreatic β cells and investigating their potential roles in normal and abnormal islet function. The development of new methods and tools for the study of individual islet cells has produced a surge of interest in this topic. RECENT FINDINGS: Studies of β cell maturation and pregnancy-induced proliferation have identified changes in serotonin and transcription factors SIX2/3 expression as markers of temporal heterogeneity. Structural and functional heterogeneity in the form of functionally distinct 'hub' and 'follower' β cells was found in mouse islets. Heterogeneous expression of Fltp (in mouse β cells) and ST8SIA1 and CD9 (in human β cells) were associated with distinct functional potential. Several impressive reports describing the transcriptomes of individual β cells were also published in recent months. Some of these reveal previously unknown β cell subpopulations. SUMMARY: A wealth of information on functional and phenotypic heterogeneity has been collected recently, including the transcriptomes of individual β cells and the identities of functionally distinct β cell subpopulations. Several studies suggest the existence of two broad categories: a more proliferative but less functional and a less proliferative but more functional β cell type. The identification of functionally distinct subpopulations and their association with type 2 diabetes underlines the potential clinical importance of these investigations.