Ontogeny of glucagon messenger RNA and encoded precursor in the rat intestine.

The ontogeny of proglucagon mRNA and encoded precursor was studied in rat intestine from day 11 of fetal gestation (E11) to maturity. The earliest time point for detection of proglucagon antigenic determinants by immunocytochemistry, and of proglucagon mRNA by in situ hybridization histochemistry, was day 14 of fetal gestation (E14), suggesting this time as the point of onset of intestinal proglucagon gene expression and mRNA translation. Between day 17 and 18 of gestation (E17 and E18) there was a significant 10 fold increase in intestinal L cell density, indicating that this time in gestation is one of increased L cell differentiation and/or proliferation. Proglucagon mRNA abundance in developing rat intestine showed a major 8 fold increase between E17 and E18. Similar magnitude of increases in L cell density and proglucagon mRNA abundance suggests that the increase in proglucagon mRNA abundance reflects an increase in L cell numbers rather than increases in proglucagon gene transcription or mRNA stability per cell.