Neural crest origin of the endocrine polypeptide (APUD) cells of the gastrointestinal tract and pancreas.

A method of labelling known to be appropriate for the demonstration of endocrine polypeptide (APUD) cells was found to label the cells of the neural crest in the chick embryo after as little as 72 hours' development. The method depends on the production, from an exogenous precursor, of an amine which is stored in specific granules and which is convertible by treatment with hot formaldehyde vapour into a fluorescent derivative. The whole technique is described as APUD-FIF. The application of APUD-FIF to mouse embryos shows that at the 7-8 somite stage (eight days) labelled neural crest cells migrate in large masses in a ventrad direction. At around the ninth day they colonize the developing foregut and its derivatives, including pharynx, stomach, duodenum, ultimobranchial body, and pancreas. In subsequent stages of development (up to 12 days) the cells are seen in comparatively large numbers in the gastrointestinal tract and in the pancreas. Complete proof that these early APUD cells, which demonstrably arise from the neural crest, are the precursors of all the endocrine polypeptide cells of the adult pancreas, stomach, duodenum, and small and large intestine, is not at present available. Notwithstanding a great deal of earlier evidence to the contrary, the premise seems likely to be true.