Accumulation of the predominant pancreatic mRNAs during embryonic development.

We have examined the pattern of accumulation of specific adult pancreas mRNAs during embryonic de- velopment by comparative analysis of the in vitro translation products of RNAs isolated from embryonic and adult pancreases. Changes in the concentration of individual mRNAs were inferred from the sodium do- decyl sulfate-polyacrylamide gel profiles of the in vitro translation products. The concentrations of several mRNAs coding for predominant adult translation prod- ucts increased dramatically between 14 and 20 days of gestation, coincident with pancreatic cytodifferentia- tion. A few prominent adult mRNAs were not detected in RNA isolated from embryonic pancreases, indicating that further qualitative changes in pancreatic gene expression occur after birth. The accumulation of the mRNA for the major secre- tory enzyme, amylase, was measured by specific im- munoprecipitation of the in vitro translation products. In vitro synthesized amylase, identified by immunopre- cipitation and by sodium dodecyl sulfate-polyacryl- amide gel separation of peptides generated by protease digestion, appeared approximately 2000 daltons larger than amylase isolated from adult pancreatic secretions. Amylase mRNA levels measured by immunoprecipita- tion of in vitro translation products increased a mini- mum of loo-fold between Days 14 and 20 of gestation, coincident with the increase in amylase synthesis. These results indicate that the rate of amylase synthe- sis during this developmental period is controlled in large part by the rate of accumulation of amylase mRNA. Enzymatic analyses have shown a biphasic accumulation of the exocrine digestive enzymes during the development of the rat pancreas (l-3). These data suggested that the developing exocrine pancreas undergoes at least two differentiative tran-