Initially tri-potent multil-ineage progenitor cells (MPCs) expressing both Pdx1 and Ptf1a ultimately give rise to ductal, islet and and acinar cells. On E11.5 most MPCs also co-express Sox9, Hnf1 β, Hnf6, Nkx6.1, and Nkx6.2. By E12.5, Hnf1 β, Hnf6, Nkx6.1, and Nkx6.2 become largely restricted to trunk progenitor cells (TrunkPCs), while Ptf1a becomes restricted to tip progenitors (TipPCs), with Notch signaling promoting the TrunkPC identity. By E13.5, acinar and lslet differentiation have been initiated, associated with the activation of additional lineage-specific transcription factors. Among TrunkPCs, Notch activation promotes a ductal fate. By the time of gestation, active Notch signaling is largely confined to centroacinar cells (CAC), whose derivation from Trunk vs. TipPCs remains unknown. CACs may be derived from either trunk progenitors maintaining active Notch signaling or from tip progenitors reactivating Notch.