Mammalian pancreas development: Regeneration and differentiation in vitro

Abstract

Studies of the temporal sequence of mammalian pancreas development have demonstrated the existence of a protodifferentiated state that is characterized by low constant levels of amylase specific activity. In order to investigate this state further, guts from 9-day mouse embryos were cultured for 3 days, during which a protodifferentiated dorsal pancreas formed, consisting of a neck region or duct that extended from the intestinal wall and terminated in a large bulb of tissue. The pancreas bulb was then removed, leaving only the duct. This day corresponded to Day 12 of gestation. During 5 days of additional culture, 37 of 43 ducts regenerated a pancreas with an amylase specific activity equal to that of control pancreas (2.4 μg of maltose hydrate released/min/μg of protein at 37°C). Guts placed in culture at 12 days, with removal of the pancreas the same day, gave similar results. Other combinations of starting embryonic age plus culture time, prior to pancreas removal, totaling 12 or 13 days also underwent regeneration. Only of 18 pancreases regenerated from ducts equivalent to 14 days of gestation. Removal of the stomach, the intestine, and the ventral pancreas did not affect the ability of the dorsal pancreas to regenerate. However, removal of the duct at the presumptive intestinal wall did not result in regeneration. Regenerated pancreas differentiation was further confirmed by electron microscopic demonstration of zymogen granules in exocrine cells and of at least two types of secretory granules in endocrine cells. The results demonstrate that the protodifferentiated duct can regenerate a new pancreas including both exocrine and endocrine tissue, and that the regenerated pancreas is not retarded in its development when compared with the control pancreas.