GLYCOGEN-PHOSPHORYLASE - DEVELOPMENTAL EXPRESSION IN RAT-LIVER

The developing fetus is vulnerable to hypoglycemia if its transplacental substrate supply is compromised. Consequently, we examined hepatic glycogen phosphorylase gene expression in the developing rat liver by comparing the relative activities of the hepatic phosphorylase enzyme, concentrations of cellular phosphorylase mRNA, and rates of transcription in isolated liver nuclei of fetal rats at 19 days of gestation, 21 days of gestation, neonatal rats, and suckling rats. Cellular phosphorylase mRNA and enzyme activity (total and phosphorylase a) increased until term. Reciprocally, the rate of phosphorylase mRNA transcription was rapid in the rats at 19 days of gestation, and declined progressively until term. These data indicate that glycogen phosphorylase gene expression is regulated post-transcriptionally in late gestation, perhaps by an increase in phosphorylase mRNA stability towards term. This results in increased phosphorylase mRNA and enzyme expression.