English: Pancreas specification within the foregut endoderm is first indicated by expression of the transcription factor Pdx1, which marks the progenitors of all exocrine and endocrine cell types. As the embryonic organ grows, multipotent progenitor cells also express the transcription factor Ptf1a and the digestive enzyme Cpa1. These progenitors are later segregated into specific sub-lineages, prior to differentiation. Acinar cells arise from precursors that express high levels of Ptf1a and Cpa1, while islet cells arise from precursors that transiently express the transcription factor Neurog3. Although Neurog3-expressing cells arise from duct-like epithelial progenitors (see Figure 2), the lineage relationship between these structures and the ducts of the mature organ is unclear (question marks).