Current techniques for the alteration of gene expression in the liver have a number of limitations, including the lack of stable somatic gene transfer and the technical challenges of germline transgenesis. Rapid and stable genetic engineering of the liver would allow systematic, in vivo testing of contributions by many genes to disease. After fumaryl acetoacetate hydrolase (Fah) gene transfer to hepatocytes, selective repopulation of the liver occurs in FAH-deficient mice. This genetic correction is readily mediated with transposons. Using this approach, we show that genes with biological utility can be linked to a selectable Fah transposon cassette. First, net conversion of Fah ؊/؊ liver tissue to transgenic tissue, and its outgrowth, was monitored by bioluminescence in vivo from a luciferase gene linked to the FAH gene. Second, coexpressed short hairpin RNAs (shRNAs) stably reduced target gene expression, indicating the potential for loss-of-function assays. Third, a mutant allele of human ␣1-antitrypsin (hAAT) was linked to Fah and resulted in protein inclusions within hepatocytes, which are the histopathological hallmark of hAAT deficiency disorder. Finally, oncogenes linked to Fah resulted in transformation of transduced hepatocytes. Conclusion: Coexpression with FAH is an effective technique for lifelong expression of transgenes in adult hepatocytes with applicability to a wide variety of genetic studies in the liver. (HEPATOLOGY 2008;47:1714-1724.) M icroarray and cancer genome sequencing projects have produced an emergent catalog of genes implicated in liver regeneration, metabolism, cancer, and inherited diseases. 1,2 In turn, there is increasing need for in vivo assessment of these genes in a meaningful context. One method for assessing cancer genes is to express putative oncogenes in primordial liver cells, transplant these cells into recipient mice, and mea-sure tumor outgrowth. 3 An easier method, in which genes could be directly and stably expressed or suppressed in most hepatocytes in vivo, would facilitate the validation and testing of genes thought to affect liver biology.
Current techniques for gene expression in the liver have limitations. Germline transgenesis establishes stable gene expression, but its expense constrains scale-up or the ready study of genetic interplay. For example, genetic