Dynamic differentiation potential within theexocrine pancreas. Multipotent pancreatic progenitors (E11.5-E13.5) express the digestive enzyme Cpa1, which is later restricted to acinar cells (E14.5-adult), together with Muc1 and Hnf1β . While Cpa1+ cells cease contribution to islets from approximately E13.5 , Muc1+/Hnf1β+ cells continue to give rise to Neurog3+ endocrine precursors (pink nuclei) and islets (blue and green) through at least E15.5. From around birth, Muc1+ and Hnf1β+ cells no longer contribute to the endocrine lineage, and mature islets are maintained by self-replication of those pre-existing. However, it remains a formal possibility that a subpopulation exists within the ductal network (dark blue cytoplasm), expressing neither Muc1 nor Hnf1β, from which β-cells continue to arise after birth.