Insulin gene expression during development of the fetal bovine pancreas.

Poly(A+) RNA was isolated from the bovine pancreas at three stages of fetal development. Approximately 1% of the total RNA from first, second, and third trimester fetuses was polyadenylated, and the mean chain length of each RNA population was 1350 nucleotides. In cell-free protein synthesis experiments the concentration of insulin-immunoreactive translation products was 10.2%, 11.3%, and 9.7% for first, second, and third trimesters, respectively. Insulin mRNA sequences were estimated by transcription of insulin mRNA to [3H]cDNA and hybridization of cDNA with plasmid pI19 DNA containing rat proinsulin I sequences. Hybridization experiments gave insulin mRNA concentrations of 7.6%, 12.9%, and 3.9% for first, second, and third trimesters, respectively. These results show that insulin mRNA levels vary during development and become proportionally lower in third trimester, when the exocrine tissue is rapidly increasing in mass.