Persistent expression of genes transferred in the fetal rat liver via retroviruses.

The transfer of genes into the fetal liver is a promising approach for correction of inborn errors in metabolism identified in prenatal life. In this study, we demonstrate that gene transfer to the fetal rat liver resulted in the stable expression of the gene in the hepatocytes of the adult animals. This was achieved by a combination of gene transfer via ecotropic retroviruses in the fetal liver with subsequent partial hepatectomy of the offspring. Replication incompetent, ecotropic and amphotropic retroviruses were used to transfer the bovine growth hormone gene (bGH) linked to the promoter (-450 to +73) for the P-enolpyruvate carboxykinase (PEPCK) gene into the fetal liver in the last trimester of gestation. Amphotropic retroviruses were unable to infect the fetal liver due to the lack of expression of their receptors. The fetal liver was infected by the ecotropic retroviruses and partial hepatectomy of the offspring at one month of age stimulated expression of the PEPCK/bGH gene in the liver over ten fold. Expression of the gene persisted for as long as one year. A heterogeneous pattern of expression of the chimeric gene throughout the liver parenchymal cells was identified with higher expression in the pericentral region of the liver. This zonation of expression was not expected, since the endogenous PEPCK gene is expressed in periportal hepatocytes. We suggest that, following partial hepatectomy DNA replication activates expression of the proviral PEPCK/bGH gene, mainly in midzonal and pericentral hepatocytes. Proviral sequences may influence the expression of the PEPCK/bGH gene in parenchymal cells in which the PEPCK promoter is not normally active.