The paper describes the cloning and characterization of insulin promoter factor 1 (IPF1), a homeodomain-containing protein that is selectively expressed in the β-cells of the adult mouse pancreas. IPF1 binds to and transactivates the insulin promoter, suggesting its role in the β-cell-specific expression of the insulin gene. In embryos, IPF1 expression begins before hormone gene expression and is restricted to the dorsal and ventral walls of the primitive foregut, where the pancreas will later form. The pattern of IPF1 expression and its ability to stimulate insulin gene transcription indicate that IPF1 functions in the regionalization of the primitive gut endoderm and the maturation of pancreatic β-cells. The study also explores the temporal and spatial expression of IPF1 in mouse embryos, showing that it is first detected at around the 13 somite stage, coinciding with the commitment of the gut endoderm to a pancreatic fate. The findings suggest that IPF1 may play a crucial role in the development and specification of pancreatic β-cells.The paper describes the cloning and characterization of insulin promoter factor 1 (IPF1), a homeodomain-containing protein that is selectively expressed in the β-cells of the adult mouse pancreas. IPF1 binds to and transactivates the insulin promoter, suggesting its role in the β-cell-specific expression of the insulin gene. In embryos, IPF1 expression begins before hormone gene expression and is restricted to the dorsal and ventral walls of the primitive foregut, where the pancreas will later form. The pattern of IPF1 expression and its ability to stimulate insulin gene transcription indicate that IPF1 functions in the regionalization of the primitive gut endoderm and the maturation of pancreatic β-cells. The study also explores the temporal and spatial expression of IPF1 in mouse embryos, showing that it is first detected at around the 13 somite stage, coinciding with the commitment of the gut endoderm to a pancreatic fate. The findings suggest that IPF1 may play a crucial role in the development and specification of pancreatic β-cells.