Direct evidence for the pancreatic lineage: NGN3+ cells are islet progenitors and are distinct from duct progenitors

TLDR

The origins of endocrine islets during embryogenesis and in adult mice remain undefined, as does the identity of adult islet stem cells. The authors employed an inducible Cre‑ERTM‑LoxP system to permanently label progeny of Ngn3‑ or Pdx1‑expressing cells at distinct developmental stages. They demonstrated that NGN3+ cells are definitive islet progenitors in embryos and adults, while Pdx1+ cells give rise to exocrine, endocrine, and duct tissues, with duct lineage segregating around E9.5–E11.5, indicating that exocrine, endocrine, and duct progenitors are committed by mid‑gestation.

Abstract

The location and lineage of cells that give rise to endocrine islets during embryogenesis has not been established nor has the origin or identity of adult islet stem cells. We have employed an inducible Cre-ERTM-LoxP system to indelibly mark the progeny of cells expressing either Ngn3 or Pdx1 at different stages of development. The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice. In addition, we find that cells expressing Pdx1 give rise to all three types of pancreatic tissue: exocrine, endocrine and duct. Furthermore, exocrine and endocrine cells are derived from Pdx1-expressing progenitors throughout embryogenesis. By contrast, the pancreatic duct arises from PDX1+ progenitors that are set aside around embryonic day 10.5 (E9.5-E11.5). These findings suggest that lineages for exocrine, endocrine islet and duct progenitors are committed at mid-gestation.