Differential gastrin gene expression in rat gastrointestinal tract and pancreas during neonatal development.

Gastrin gene expression exhibits a complex pattern of tissue-specific expression during the neonatal development of the gastrointestinal tract and pancreas. In the rat fetus, the pancreas is the major site of gastrin expression; very little gastrin is found in the antrum which is the major site of adult expression. Pancreatic gastrin mRNA is identical to the antral species having the same transcriptional initiation site. The post-translational processing of the pancreatic gastrin peptide, however, differs in being fully tyrosine sulfated, and thus it resembles gastrin's homologue, cholecystokinin. Pancreatic gastrin is maximally expressed during late fetal gestation before the marked rise in somatostatin, insulin, and glucagon mRNA levels which occurs during the last 4 days of gestation. After birth, gastrin mRNA levels rapidly disappear as the other islet mRNAs achieve stable maximal levels. Unlike the pancreas, gastrin gene expression in the duodenum and antrum is similar to the development profiles of somatostatin and glucagon gene expression. In the duodenum, however, expression of cholecystokinin differs from the common developmental pattern in being expressed only after birth. Thus, pancreatic gastrin gene expression shows a reciprocal relationship to the developmental expression of cholecystokinin in the duodenum.