Initiation of gastrin expression during the development of the mouse pancreas.

Gastrin expression occurs in the pancreas in only two situations: (1) in cases of gastrinoma and (2) in the embryonic/fetal pancreas. The initiation of gastrin expression in the embryonic pancreas may be recapitulated during gastrinoma tumorigenesis. For this reason, we have tried to identify the point of onset of gastrin expression in the developing pancreas. Previously, determining the point of onset for genes in embryonic tissues has been difficult because of low expression levels and small tissue samples. Using the sensitive polymerase chain reaction assay, we were able to determine, with a sensitivity of 10 molecules of mRNA, the earliest expression of gastrin in the developing pancreas. This expression occurred at 30 somites, or at a gestation of 9.5 to 10 days.