BACKGROUND & AIMS Augmenter of liver regeneration (ALR, encoded by GFER) is a widely distributed pleiotropic protein originally identified as a hepatic growth factor. However, little is known about its roles in hepatic physiology and pathology. We created mice with liver-specific deletion of ALR to study its function. METHODS We developed mice with liver-specific deletion of ALR (ALR-L-KO) using the albumin-Cre/LoxP system. Liver tissues were collected from ALR-L-KO mice and ALRfloxed/floxed mice (controls) and analyzed by histology, reverse-transcription PCR, immunohistochemistry, electron microscopy, and techniques to measure fibrosis and lipids. Liver tissues from patients with and without advanced liver disease were determined by immunoblot analysis. RESULTS Two weeks after birth, livers of ALR-L-KO mice contained low levels of ALR and ATP; they had reduced mitochondrial respiratory function and increased oxidative stress, compared with livers from control mice, and had excessive steatosis, and hepatocyte apoptosis. Levels of carbamyl-palmitoyl transferase 1a and ATP synthase subunit ATP5G1 were reduced in livers of ALR-L-KO mice, indicating defects in mitochondrial fatty acid transport and ATP synthesis. Electron microscopy showed mitochondrial swelling with abnormalities in shapes and numbers of cristae. From weeks 2–4 after birth, levels of steatosis and apoptosis decreased in ALR-L-KO mice, whereas numbers of ALR-expressing cells increased, along with ATP levels. However, at weeks 4–8 after birth, livers became inflamed, with hepatocellular necrosis, ductular proliferation, and fibrosis; hepatocellular carcinoma developed by 1 year after birth in nearly 60% of the mice. Hepatic levels of ALR were also low in ob/ob mice and alcohol-fed mice with liver steatosis, compared with controls. Levels of ALR were lower in liver tissues from patients with advanced alcoholic liver disease and nonalcoholic steatohepatitis than in control liver tissues. CONCLUSIONS We developed mice with liver-specific deletion of ALR, and showed that it is required for mitochondrial function and lipid homeostasis in the liver. ALR-L-KO mice provide a useful model for investigating the pathogenesis of steatohepatitis and its complications.

Parental genomic imprinting refers to the phenomenon by which alleles behave differently depending on the sex of the parent from which they are inherited. In the ease of the routine transgene RSVIgmyc, imprinting is manifest in two ways: differential DNA methylation and differential expression. In inbred FVB/N mice, a transgene inherited from a male parent is undermethylated and expressed; a transgene inherited from the female parent is overmethylated and silent. Using a series of RSVIgmyc constructs and transgenie mice, we show that the imprinting of this transgene requires a c/s-acting signal that is principally derived from the repeat sequences that make up the 3' portion of the murine immunoglobulin a heavy-chain switch region. Such imprinting is relatively independent of the site of transgene insertion but is influenced by the structure of the transgene itself. Imprinting is also modulated by genetic background. Detailed studies indicate that the paternal allele is undermethylated and expressed in inbred FVB/N mice and in heterozygous F~ FVB/N/C57BI/6J mice but is overmethylated and silent in inbred C57B1/6J mice. Consequently, the FVB/N genome appears to carry alleles of modulating genes that dominantly block methylation and permit expression of the paternally imprinted transgene. Furthermore, our results suggest that overmethylation is the default status of both parental alleles and that the paternal allele can be marked in trans by polymorphic factors that act in postblastocyst embryos.

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By means of low-stringency cross-species hybridization to Southern DNA blots, human c-jun sequences were used to identify a unique Drosophila melanogaster locus (Djun). The predicted DJun protein is highly homologous to members of the mammalian Jun family in both the DNA binding and leucine zipper regions. Djun was mapped by in situ hybridization to position 46E of the second chromosome. It encodes a 1.7-kilobase transcript constitutively expressed at all developmental stages. Functionally, Djun in cooperation with mouse c-fos can trans-activate activator protein 1 DNA binding site when introduced into mammalian cells. Taken together, these data suggest that Djun, much like its mammalian homolog, may activate transcription of genes involved in regulation of cell growth, differentiation, and development. Furthermore, the identification of Djun allows one to exploit the genetics of Drosophila to identify genes in signal transduction pathways involving Djun and thus c-jun.