Changes in the frequency of specific transcripts during development of the pancreas

The sequence complexity and frequency distribution of adult rat pancreas polyadenylated RNAs and the changes in these pancreas transcripts during development have been analyzed by means of complementary DNA-RNA hybridization analysis. The following results were obtained. An abundant set of pancreas polyadenylated RNAs hybridizes with 90% of pancreas cDNA (the copy of adult rat pancreas polyadenylated RNA), comprises about 2% of total pancreas RNA, has a sequence complexity of about 2 x 10 ⁴ nucleotides, and is largely tissue specific. These and other data imply that these RNAs code primarily for pancreas-specific secretory proteins. A less abundant set of pancreas RNAs hybridizes with HTC (a rat tumor line) cell cDNA (the copy of HTC cell polyadenylated RNA), comprises about 0.03% of total pancreas RNA, has a sequence complexity of at least 3 x 10 ⁵ nucleotides, and is more frequent in rapidly proliferating tissues (HTC cells and embryonic pancreas) than in the adult pancreas. In contrast to the pancreas, the relatively undifferentiated HTC cell does not contain a predominant set of polyadenylated RNAs of low complexity. Moderate concentrations of RNAs complementary to pancreas cDNA are present in pancreatic rudiments at 14 days of gestation when levels of pancreas-specific proteins are low. Between 14 and 20 days of gestation, the concentration of these RNAs increases several 100-fold in the embryonic pancreas, in parallel with the increased rate of synthesis of pancreas-specific proteins. Pancreas cDNA hybridizes in situ primarily to the regions of acinar cells actively synthesizing secretory proteins. The very favorable signal-to-noise ratio of the technique indicates that it will be useful for detecting low amounts of pancreas-specific RNAs early in development.