The two nonallelic rat insulin mRNAs and pre-mRNAs are regulated coordinately in vivo

These studies compared the regulation of expression of the two nonallelic rat insulin genes in vivo. The relative abundance of mRNAs for rat insulins I and II was the same in sucrose-treated and fasted rats despite 2-fold higher total insulin mRNA levels in sucrose-treated groups. The ratio of rat insulin I to rat insulin II mRNA also remained constant when demand for insulin was increased by pregnancy, administration of dexamethasone, or excess growth hormone. The two mRNAs for insulin appeared at the same time during fetal pancreatic development, increased in constant proportion to maximum values during the neonatal period, and fell in tandem to adult values by age 6 weeks. Taken together, these data suggest that similar or identical mechanisms modulate steady-state levels of both insulin mRNAs in rats. Concentrations of precursors for each mRNA were also greater in sucrose-treated rats, indicating that changes in mRNA concentrations were mediated at least in part by changes in either gene transcription rates or in mRNA precursor stability.