Figure 2. Developmental potency of Sox9⁺ cells becomes progressively restricted during pancreogenesis.

A: Genetic lineage tracing has shown that during the primary transition, Sox9 defines multipotent MPCs (also marked by Pdx1 and Ptf1a) comprising the pancreatic epithelium which give rise to all three pancreatic compartments: exocrine acinar (A), ductal (D), and endocrine (E) cells (via an intermediate Ngn3⁺ endocrine progenitor cell). B: Concurrently with branching and proximodistal patterning of the pancreatic epithelium between approximately E11.5-12.5, Sox9 continues to mark MPCs with an increased propensity to give rise to ductal and endocrine cells at the expense of acinar cells. C: During the secondary transition, Sox9 expression defines bipotent progenitor cells which almost exclusively yield ductal or endocrine cells; Sox9⁺ cells at the extreme distal ends of the trunk can, however, yield acinar cells. D: By late gestation, Sox9⁺ cells predominantly contribute to the ductal compartment; they can, however, still yield endocrine cells and, very rarely, acinar cells. E: During the first three weeks of life, Sox9⁺ cells almost exclusively yield ductal cells; endocrine neogenesis can, however, still rarely occur from the Sox9⁺ compartment. F: In contrast, in later adulthood, Sox9⁺ cells are unipotent, giving rise only to ductal cells. Thickness of arrows denotes relative propensity to yield cells of each of the three pancreatic compartments.