Pancreatic multipotent progenitor cells (MPCs) produce acinar, endocrine and duct cells during organogenesis, but their existence and location in the mature organ remain contentious. We used inducible lineage-tracing from the MPC-instructive gene Ptf1a to define systematically in mice the switch of Ptf1a⁺ MPCs to unipotent proacinar competence during the secondary transition, their rapid decline during organogenesis, and absence from the mature organ. Between E11.5 and E15.5, we describe tip epithelium heterogeneity, suggesting that putative Ptf1a⁺Sox9⁺Hnf1β⁺ MPCs are intermingled with Ptf1a^HISox9^LO proacinar progenitors. In the adult, pancreatic duct ligation (PDL) caused facultative reactivation of multipotency factors (Sox9 and Hnf1β) in Ptf1a⁺ acini, which undergo rapid reprogramming to duct cells and longer-term reprogramming to endocrine cells, including insulin⁺ β-cells that are mature by the criteria of producing Pdx1^HI, Nkx6.1⁺ and MafA⁺. These Ptf1a lineage-derived endocrine/β-cells are likely formed via Ck19⁺/Hnf1β⁺/Sox9⁺ ductal and Ngn3⁺ endocrine progenitor intermediates. Acinar to endocrine/β-cell transdifferentiation was enhanced by combining PDL with pharmacological elimination of pre-existing β-cells. Thus, we show that acinar cells, without exogenously introduced factors, can regain aspects of embryonic multipotentiality under injury, and convert into mature β-cells.

Regulatory proteins have been identified in embryonic development of the endocrine pancreas. It is unknown whether these factors can also play a role in the formation of pancreatic endocrine cells from postnatal nonendocrine cells. The present study demonstrates that adult human pancreatic duct cells can be converted into insulin-expressing cells after ectopic, adenovirus-mediated expression of the class B basic helix-loop-helix factor neurogenin 3 (ngn3), which is a critical factor in embryogenesis of the mouse endocrine pancreas. Infection with adenovirus ngn3 (Adngn3) induced gene and/or protein expression of NeuroD/β2, Pax4, Nkx2.2, Pax6, and Nkx6.1, all known to be essential for β-cell differentiation in mouse embryos. Expression of ngn3 in adult human duct cells induced Notch ligands Dll1 and Dll4 and neuroendocrine- and β-cell–specific markers: it increased the percentage of synaptophysin- and insulin-positive cells 15-fold in ngn3-infected versus control cells. Infection with NeuroD/β2 (a downstream target of ngn3) induced similar effects. These data indicate that the Delta-Notch pathway, which controls embryonic development of the mouse endocrine pancreas, can also operate in adult human duct cells driving them to a neuroendocrine phenotype with the formation of insulin-expressing cells.

This study demonstrates that rat islet beta cells constitutively express an apoptotic program which is activated when mRNA or protein synthesis is blocked. Apoptotic beta cells were detectable by electron microscopy after treatment with actinomycin D or cycloheximide. With a fluorescence microscopic assay both agents were found to increase the number of apoptotic beta cells dose- and time-dependently, up to 70% after 1 wk of culture; virtually no apoptotic beta cells occurred in control preparations or in conditions leading to primary necrosis. Thus, survival of beta cells seems dependent on synthesis of proteins which suppress an endogenous suicide program. This mechanism explains earlier observed effects of glucose on survival of cultured beta cells. Glucose is known to dose-dependently increase the percentage of beta cells in active biosynthesis and the percentage that survives during culture. It is now demonstrated that the glucose-induced survival of beta cells cultured for 1 wk results from a dose-dependent reduction in the percentage of beta cells dying in apoptosis (49% at 3 mM glucose, 40% at 6 mM, 9% at 10 mM). Thus, intercellular differences in glucose sensitivity appear responsible for the heterogeneity in beta cell sensitivity to apoptotic conditions. These data indicate that glucose promotes survival of beta cells by activating synthesis of proteins which suppress apoptosis. The present model allows for further investigation of the regulation of apoptosis in beta cells and the identification of agents which induce or prevent beta cell death.

EMBO Press is an editorially independent publishing platform for the development of EMBO scientific publications.

The epigenome changes that underlie cellular differentiation in developing organisms are poorly understood. To gain insights into how pancreatic beta-cells are programmed, we profiled key histone methylations and transcripts in embryonic stem cells, multipotent progenitors of the nascent embryonic pancreas, purified beta-cells, and 10 differentiated tissues. We report that despite their endodermal origin, beta-cells show a transcriptional and active chromatin signature that is most similar to ectoderm-derived neural tissues. In contrast, the beta-cell signature of trimethylated H3K27, a mark of Polycomb-mediated repression, clusters with pancreatic progenitors, acinar cells and liver, consistent with the epigenetic transmission of this mark from endoderm progenitors to their differentiated cellular progeny. We also identified two H3K27 methylation events that arise in the beta-cell lineage after the pancreatic progenitor stage. One is a wave of cell-selective de novo H3K27 trimethylation in non-CpG island genes. Another is the loss of bivalent and H3K27me3-repressed chromatin in a core program of neural developmental regulators that enables a convergence of the gene activity state of beta-cells with that of neural cells. These findings reveal a dynamic regulation of Polycomb repression programs that shape the identity of differentiated beta-cells.