DEVELOPMENTAL AND GLUCOCORTICOID MODULATION OF THE EXPRESSION OF MESSENGER-RNAS FOR G(S-ALPHA) AND G(BETA) SUBUNITS IN NEONATAL LIVER

The mRNA levels for G(S alpha) and G(beta) in liver from various age groups of rabbits were assessed by Northern and dot-blot hydridization assays using cDNA and oligonucleotide probes. The mRNA levels for both G(S alpha) and G(beta) exhibited a transient 30-35% decrease at 3-6 h after birth, followed by a 3- to 3.5-fold increase which peaked at 2 days after birth, then gradually declined to adult levels at 4-6 weeks. The changes in mRNA levers paralleled the changes in protein levels [previously measured by immunoblotting (Kawai and Arinze, 1991)] in the first 2 days after birth, but not in the later periods of development. Beyond day 3, the increase in protein levels persists, reaching maximal levers at 4 weeks and equalling adult levels while their mRNA levels decrease to about 50% of the levels at day 2. In vivo administration of dexamethasone to neonatal rabbits increased hepatic mRNA levels for both G(S alpha) and G(beta) by about 50%; the effect was moderate compared to the 2- to 3-fold increase in corresponding protein levels. The transcription rate for the G(S alpha) gene increased by only 32% at day 2 after birth compared to term. A 68% increase in transcription rate for this gene was observed after the dexamethasone treatment. Taken together, these data indicate that the developmental and glucocorticoid-regulated expression of G(S alpha)- and G(beta)-subunits in neonatal liver is modulated at the transcriptional level.