PDX1 cells are necessary in pancreatic development because the fates of pancreatic cells are controlled by downstream transcription factors; PDX1 epithelial cells give rise to pancreatic buds and eventually the whole pancreas.
In vertebrates, Pdx1 is necessary for pancreatic development, including -cell maturation, and duodenal differentiation. Pdx1 is accepted as the earliest marker for pancreatic differentiation, with the fates of pancreatic cells controlled by downstream transcription factors. In pancreatic development, Pdx1 is expressed by a population of cells in the posterior foregut region of the definitive endoderm, and Pdx1 epithelial cells give rise to the developing pancreatic buds, and eventually, the whole of the pancreasits exocrine, endocrine, and ductal cell populations. 
