Molecular insights into the development of the pancreas

There is general agreement that the exocrine pancreas derives from the endoderm of the embryonic foregut. The cellular origin of the endocrine pancreas has been debated for a long time. A hypothesis existed that the endocrine cells of the pancreas originated from the neural crest of the embryo. The recent application of microdissection of the mouse embryo and an exquisitely sensitive polymerase chain reaction assay (PCR) indicates that both the exocrine and endocrine cells of the pancreas develop from the endoderm of the foregut as evidenced by the expression of genes responsible for acinar enzymes and islet hormones in the foregut at the site where the future pancreatic diverticulum would form. Furthermore, the mesenchyme surrounding the primitive endoderm cells from which the pancreas would form exerts significant regulation of differentiation of the pancreas. In culture or in vivo explants, these endoderm cells differentiate only into islet cells in the absence of mesenchyme. On the other hand, when these cells are cultured in vitro with mesenchyme, they differentiate to form not only islets but also ducts and acini.