Regulation of glutamate dehydrogenase expression in the developing rat liver: control at different levels in the prenatal period.

To study the regulation of the expression of glutamate dehydrogenase (Glu-DH) in rat liver during development, the Glu-DH mRNA concentration in the liver of rats ranging in age from 14 days prenatal development to 3 months after birth was determined. This concentration increased up to two days before birth, decreased rapidly between two days before and one day after birth and increased again in the second and third postnatal week. The ratio of Glu-DH mRNA/protein decreased more than 10-fold in the prenatal period, whereas it did not change significantly after birth. Thus, whereas the ratio between the Glu-DH monomer protein molecules and Glu-DH mRNA molecules is found to be approximately 1400 at 14 days of prenatal development, it is approximately 1700 four weeks after birth. We argue than an increase in the translational efficiency after birth is the most likely cause of the observed developmental changes in Glu-DH mRNA/protein ratio. Our results suggest that the expression after birth is predominantly regulated at the pretranslational level, whereas the prenatal Glu-DH expression is regulated both at the translational level and at the pretranslational level.