Pax4 and Arx Represent Crucial Regulators of the Development of the Endocrine Pancreas

The development of the endocrine pancreas is under the control of highly orchestrated, cross-interacting transcription factors. Pancreas genesis is initiated by the emergence of a Pdx1/Ptf1a marked territory at the foregut/midgut junction. A small fraction of pancreatic fated cells activates the expression of the bHLH transcription factor Ngn3 triggering the endocrine cell program, thus giving rise to beta-, alpha-, delta-, PP-, and epsilon-cells, producing insulin, glucagon, somatostatin, pancreatic polypeptide, and ghrelin, respectively. Two transcription factors, Pax4 and Arx, play a crucial role in differential endocrine cell subtype specification. They were shown to be necessary and sufficient to endow endocrine progenitors with either a beta- or alpha-cell destiny. Interestingly, whereas the forced expression of Arx in beta-cells converts these into cells exhibiting alpha- and PP-cell characteristics, the sole expression of Pax4 in alpha-cells promotes alpha-cell-neogenesis and the acquisition of beta-cell features, the resulting beta-like cells being capable of counteracting chemically induced diabetes. Gaining new insights into the molecular mechanisms controlling Pax4 and Arx expression in the endocrine pancreas may therefore pave new avenues for the therapy of diabetes