Loss of pdx1 prevents the formation of the pancreas, while overexpression of endocrine-specific transcription factor, ngn3, in foregut endoderm will result in an immature pancreas containing only α cells. Loss of ngn3 expression in these cells prevents endocrine development. pdx1 positive progenitors develop both trunk and tip progenitors, ngn3 expression in trunk progenitor then leads those into an endocrine lineage and generates all four endocrine cell types. Pdx1 and MafA expression in select endocrine progenitors gave way to β cells, while MafB expression is required for α cell formation. Forced expression on pdx1, MafA, and ngn3 in acinar cells reprograms them into β cells, while forced expression of pdx1 and MafA in α cells converts them to β cells.