"The prevailing view is if we understood how the process occurs normally, we might be able to apply that information to faithfully and efficiently push the cells down the pathway to ultimately generate beta cells that may be used clinically," she says.
The new findings represent a previously unknown role for Pdx1. Endocrine precursor cell development is controlled by a DNA-binding transcription factor called neurogenin-3 (Ngn3). Ngn3, in turn, is regulated by four additional proteins: Sox9, Foxa2, Hnf6, and Hnf1b. In short, this study found that Pdx1 binds directly to the Ngn3 gene to orchestrate gene expression with these proteins.
Specifically, Stoffers was curious about the function of one end of the Pdx1 protein the C terminus whose role in beta-cell development was not known and yet is mutated in certain diseases. Her team, led by MD-PhD candidate Jennifer Oliver-Krasinski, developed mice that lacked the C terminus, essentially with a shortened Pdx1 protein.
The team found that when both copies of the Pdx1 gene were truncated at the C terminus, the pancreas formed, but the mice quickly developed diabetes. When they investigated why, they found that these mice were deficient in all endocrine cells, including beta cells.
"That led us to conclude the defect was at an early cell, or precursor, stage," Stoffers says specifically, in the formation of Ngn3-expressing endocrine progenitor cells.
Further molecular characterization of these mutant mice led the team to conclude that Pdx1 is a master regulator of the development of endocrine cell precursors. Pdx1 binds directly to the Ngn3 gene, controlling its expression; it does this by forming a molecular complex with the protein Hnf6, which is mediated by the Pdx1 C terminus. Pdx1 also binds directly to and controls the expression of t
|Contact: Karen Kreeger|
University of Pennsylvania School of Medicine