Changes in argininosuccinate lyase gene expression in the rat liver during development.

Expression of the hepatic enzyme argininosuccinate lyase (ASL), one of the urea cycle enzymes, was analyzed during the perinatal period in the rat. To this end, ASL was purified, an ELISA assay was established to quantify the enzyme protein and a cDNA clone was used to measure the amount of specific mRNA in the liver in various stages of development. During the last few days of fetal life, both enzyme and hybridizable RNA were present at levels far below those measured in the fully differentiated adult liver. Just after birth, they increased rapidly and the mRNA accumulation, particularly, could result from an enhanced rate of transcription as suggested by the experiment with actinomycin D. This postnatal shift in ASL expression was also linked to adrenal activation at birth, as shown by adrenalectomy. However, the extent to which the ASL protein accumulated after birth appeared to be limited when compared to mRNA accumulation, suggesting control mechanisms at the translational level. Thus, during the perinatal period of the rat, both transcriptional and translational control might be implicated in the expression of the ASL gene.