In situ hybridization with 33P-labeled RNA probes for determination of cellular expression patterns of liver transcription factors in mouse embryos

Hepatocyte nuclear factor 4alpha is implicated in endoplasmic reticulum stress-induced acute phase response by regulating expression of cyclic adenosine monophosphate responsive element binding protein H

Loss of the nuclear hormone receptor hepatocyte nuclear factor 4alpha (HNF4alpha) in hepatocytes results in a complex pleiotropic phenotype that includes a block in hepatocyte differentiation and a severe disruption to liver function. Recent analyses have shown that hepatic gene expression is severely affected by the absence of HNF4alpha, with expression of 567 genes reduced by > or =2.5-fold (P < or = 0.05) in Hnf4alpha(-/-) fetal livers. Although many of these genes are direct targets, HNF4alpha has also been shown to regulate expression of other liver transcription factors, and this raises the possibility that the dependence on HNF4alpha for normal expression of some genes may be indirect. We postulated that the identification of transcription factors whose expression is regulated by HNF4alpha might reveal roles for HNF4alpha in controlling hepatic functions that were not previously appreciated. Here we identify cyclic adenosine monophosphate responsive element binding protein H (CrebH) as a transcription factor whose messenger RNA can be identified in both the embryonic mouse liver and adult mouse liver and whose expression is dependent on HNF4alpha. Analyses of genomic DNA revealed an HNF4alpha binding site upstream of the CrebH coding sequence that was occupied by HNF4alpha in fetal livers and facilitated transcriptional activation of a reporter gene in transient transfection analyses. Although CrebH is highly expressed during hepatogenesis, CrebH(-/-) mice were viable and healthy and displayed no overt defects in liver formation. However, upon treatment with tunicamycin, which induces an endoplasmic reticulum (ER)-stress response, CrebH(-/-) mice displayed reduced expression of acute phase response proteins.

CONCLUSION

These data implicate HNF4alpha in having a role in controlling the acute phase response of the liver induced by ER stress by regulating expression of CrebH.

Development of the mammalian liver and ventral pancreas is dependent on GATA4

BACKGROUND

In the mouse, the parenchyma of both the liver and ventral pancreas is specified from adjacent domains of the ventral foregut endoderm. GATA4, a zinc finger transcription factor, is strongly expressed in these endodermal domains and molecular analyses have implicated GATA4 in potentiating liver gene expression during the onset of hepatogenesis. We therefore hypothesized that GATA4 has an integral role in controlling the early stages of pancreatic and liver development.

RESULTS

To determine whether GATA4 contributes to development of either the pancreas or liver we characterized the formation of pancreatic and hepatic tissues in embryos derived from Gata4-/- ES cells by tetraploid embryo complementation. In the absence of GATA4, development of the liver and ventral pancreas was disrupted. At embryonic day (E) 9.5, the liver bud failed to expand although, contrary to expectations, the hepatic endoderm was able to form a pseudo-stratified epithelial liver bud that expressed hepatic genes. Moreover, as we had shown previously, the embryos lacked septum transversum mesenchyme suggesting that liver defects may be cell non-autonomous. Analyses of pancreatic development revealed a complete absence of the ventral but not the dorsal pancreas in Gata4-/- embryos. Moreover, Gata6-/- embryos displayed a similar, although less dramatic phenotype, suggesting a critical role for multiple GATA factors at the earliest stages of ventral pancreas development.

CONCLUSION

This study defines integral roles for GATA factors in controlling early development of the mammalian liver and pancreas.

GATA6 is essential for embryonic development of the liver but dispensable for early heart formation

Several lines of evidence suggest that GATA6 has an integral role in controlling development of the mammalian liver. Unfortunately, this proposal has been impossible to address directly because mouse embryos lacking GATA6 die during gastrulation. Here we show that the early embryonic deficiency associated with GATA6-knockout mice can be overcome by providing GATA6-null embryos with a wild-type extraembryonic endoderm with the use of tetraploid embryo complementation. Analysis of rescued Gata6-/- embryos revealed that, although hepatic specification occurs normally, the specified cells fail to differentiate and the liver bud does not expand. Although GATA6 is expressed in multiple tissues that impact development of the liver, including the heart, septum transversum mesenchyme, and vasculature, all are relatively unaffected by loss of GATA6, which is consistent with a cell-autonomous requirement for GATA6 during hepatogenesis. We also demonstrate that a closely related GATA factor, GATA4, is expressed transiently in the prehepatic endoderm during hepatic specification and then lost during expansion of the hepatic primordium. Our data support the proposal that GATA4 and GATA6 are functionally redundant during hepatic specification but that GATA6 alone is available for liver bud growth and commitment of the endoderm to a hepatic cell fate.

Dual promoter structure of ZFP106: regulation by myogenin and nuclear respiratory factor-1

The WD40 repeats containing zinc finger protein 106 (ZFP106) is a conserved mammalian protein of unknown function. However, its cDNA shares an extended region of identity with the scr homology domain 3 binding protein 3 (Sh3bp3) cDNA encoding a protein implicated in the insulin signaling pathway. Asking, whether Zfp106 and Sh3bp3 are products of the same gene, we characterized the structures and transcriptional regulation of Zfp106 and its human homologue, ZFP106. A TATA-less, CpG island associated promoter (P1), was mapped by 5'-RACE to a region 19 kb upstream of the ZFP106 translation start site. P1 is active throughout development and at low levels in all adult tissues examined. A conserved cis-element in the proximal P1 region showed specific binding to nuclear respiratory factor-1 (NRF-1). Mutagenesis of this site and transfection of a dominant-negative NRF-1 both revealed the crucial role of NRF-1 in activation of P1. The broad tissue expression of P1 was in contrast to the high level of ZFP106 mRNA observed in striated muscle. This prompted additional 5'-RACE experiments that established a second, TATA box-containing promoter (P2) upstream of the third coding exon. P1 and P2 transcripts encode proteins with distinct N-terminal sequences, with Sh3bp3 corresponding to a rare, alternatively spliced P2 transcript. P2 initiated transcripts are specifically expressed in striated muscle and their level is strongly upregulated during myogenic, but not adipogenic differentiation. By deletion analysis, the region between nucleotides -296 to +96 was sufficient for robust P2 responsiveness to myogenic differentiation. This response is mediated by the additive effect of binding of myogenin to three critical E boxes within this region. In addition, transcriptional enhancer factor-1 family factors contribute to both basal and myogenesis induced P2 activity. In situ hybridization of mouse embryos confirmed predominant expression of Zfp106 in tissues with high developmental expression of either NRF-1 (brown fat and developing brain) or myogenin (striated muscle). Our results suggest distinct roles of tissue-specific ZFP106 isoforms in growth related metabolism and provide the foundation for further studies into the regulation and function of ZFP106.

Regulation of photoreceptor Per1 and Per2 by light, dopamine and a circadian clock

In the Xenopus laevis retina, a principal model for retinal circadian organization, photoreceptors have all the properties of circadian oscillators. However, rhythmic oscillations of Per1 gene expression in the inner retina (but not photoreceptors) have been reported in mice with the suggestion that mice and frogs have a different retinal circadian organization. Although it is known that two period genes (xPer1 and xPer2) exhibit different temporal patterns of expression in the Xenopus retina, and that one (xPer2) is directly responsive to light and dopamine, it is not known whether this reflects the properties of period genes within photoreceptor oscillators or among distinct retinal cell populations. We addressed this by determining the cellular site of light and dopamine regulated xPer2 expression, and the diurnal expression of both xPer1 and xPer2 using in situ hybridization. Our data show that both xPer1 and xPer2 are expressed in most cell types in the retina, including inner nuclear neurons and ganglion cells. However, light and quinpirole, a dopamine agonist, increase xPer2 levels specifically in photoreceptors, and the effect of quinpirole, but not light, is blocked by pCPT-cAMP. Furthermore, antiphasic diurnal expression of xPer1 and xPer2 also occurs in photoreceptors. Our analysis does not provide insight into the near constitutive expression of period genes in the inner retina, but supports a model in which light- and dopamine regulated-xPer2 and rhythmic xPer1 play critical roles in entrainment and circadian oscillations within photoreceptors.

Abnormal glucose homeostasis due to chronic hyperresistinemia

Resistin is an adipocyte-secreted protein that circulates at increased levels in obesity. Acute administration of resistin impairs glucose tolerance, but the effects of chronic hyperresistinemia have not been established. Here we describe the generation and characterization of transgenic mice that have high circulating levels of resistin in the setting of normal weight. Fasted blood glucose was higher in resistin-transgenic mice than in their nontransgenic littermates, and glucose tolerance was impaired in the hyperresistinemic mice. Metabolic studies in the setting of a hyperinsulinemic-euglycemic clamp protocol revealed that chronically hyperresistinemic mice have elevated glucose production. This increase in glucose production may be partly explained by increased expression of hepatic phosphoenolpyruvate carboxykinase. Thus, chronic hyperresistinemia impairs normal glucose metabolism.

The fetoprotein transcription factor (FTF) gene is essential to embryogenesis and cholesterol homeostasis and is regulated by a DR4 element

The fetoprotein transcription factor (FTF) gene was inactivated in the mouse, with a lacZ gene inserted inframe into exon 4. LacZ staining of FTF+/- embryos shows that the mFTF gene is activated at initial stages of zygotic transcription. FTF gene activity is ubiquitous at the morula and blastocyst stages and then follows expression patterns indicative of multiple FTF functions in fetal development. FTF-/- embryos die at E6.5-7.5, with features typical of visceral endoderm dysfunction. Adult FTF+/- mice are hypocholesterolemic, and express liver FTF at about 40% of the normal level. Overexpression of liver FTF in transgenic mice indicates in vivo that FTF is an activator of CYP7A1. However, CYP7A1 expression is increased in FTF+/- liver. Gene expression profiles indicate that higher CYP7A1 expression is caused by attenuated liver cell stress signaling. Diet experiments support a model where FTF is quenched both by activated c-Jun, and by SHP as a stronger feedback mechanism to repress CYP7A1. A DR4 element is conserved in the FTF gene promoter and activated by LXR-RXR and TR-RXR, qualifying the FTF gene as a direct metabolic sensor. Liver FTF increases in rats treated with thyroid hormone or a high cholesterol diet. The FTF DR4 element tightens functional links between FTF and LXRalpha in cholesterol homeostasis and can explain transient surges of FTF gene activities during development and FTF levels lower than predicted in FTF+/- liver. The FTF-lacZ mouse establishes a central role for FTF in developmental, nutritive, and metabolic functions from early embryogenesis through adulthood.

Gene expression cascades in pancreatic development

The specialized endocrine and exocrine cells of the pancreas originally derive from a pool of apparently identical cells in the early gut endoderm. Serial changes in their gene expression program, controlled by a hierarchy of pancreatic transcription factors, direct this progression from multipotent progenitor cell to mature pancreatic cell. When the cells differentiate, this hierarchy of factors coalesces into a network of factors that maintain the differentiated phenotype of the cells. As we develop an understanding of the pancreatic transcription factors, we are also acquiring the tools with which we can ultimately control pancreatic cell differentiation.

Increased hepatic Forkhead Box M1B (FoxM1B) levels in old-aged mice stimulated liver regeneration through diminished p27Kip1 protein levels and increased Cdc25B expression

Recent liver regeneration studies indicate that maintaining hepatic Forkhead Box M1B (FoxM1B) expression in 12-month-old (old-aged) Transthyretin-FoxM1B transgenic mice increases hepatocyte proliferation and expression of cell cycle regulatory genes. Because these transgenic CD-1 mice maintain FoxM1B levels during the aging process, we conducted the current study to determine whether adenovirus delivery of the FoxM1B gene (AdFoxM1B) is sufficient to stimulate liver regeneration in old-aged Balb/c mice. Here we show that AdFoxM1B infection of old-aged mice caused a significant increase in FoxM1B expression, hepatocyte DNA replication, and mitosis following partial hepatectomy. This stimulation in hepatocyte S-phase progression was associated with diminished protein expression and perinuclear localization of cyclin-dependent kinase (Cdk) inhibitor p27(Kip1) (p27) protein following partial hepatectomy. In contrast, old-aged mice infected with control virus displayed high hepatocyte levels of p27 protein, which had been localized to the nucleus prior to S-phase. Furthermore, we found that restoring FoxM1B expression did not influence p27 mRNA levels, and this new finding implicates FoxM1B in regulation of p27 protein levels. Likewise, AdFoxM1B-infected regenerating livers displayed elevated S-phase levels of Cdk2 kinase activity compared with old-aged mice infected with control virus. Furthermore, restoring FoxM1B expression in old-aged mice caused elevated levels of Cyclin B1, Cyclin B2, Cdc25B, Cdk1, and p55CDC mRNA as well as stimulating Cdc25B nuclear localization during liver regeneration, all of which are required for mitosis. These studies indicated that an acute delivery of the FoxM1B gene in old-aged mice is sufficient to re-establish proliferation of regenerating hepatocytes, suggesting that FoxM1B can be used for therapeutic intervention to alleviate the reduction in cellular proliferation observed in the elderly.

Diminished hepatic expression of the HNF-6 transcription factor during bile duct obstruction

Hepatocyte nuclear factor 6 (HNF-6) is a member of the one cut family of transcription factors and potentially regulates expression of numerous target genes important for hepatocyte function. In the liver, HNF-6 is expressed not only in hepatocytes, but also in biliary epithelial cells (BEC). To evaluate the in vivo function of HNF-6, we examined the hepatic expression pattern of HNF-6 messenger RNA (mRNA) and protein after bile duct ligation (BDL)-mediated liver injury. We found that HNF-6 protein levels in BEC and hepatocytes were diminished within 15 hours of BDL injury and remained suppressed through the fifth day of injury. The onset of BEC proliferation in response to bile duct obstruction was associated with diminished HNF-6 protein levels. To maintain hepatic HNF-6 protein levels during BDL liver injury, we used mouse tail vein injections with recombinant adenovirus expressing HNF-6 complementary DNA (cDNA) (AdH6). We found that maintaining hepatic HNF-6 levels with AdH6 infection resulted in significant decreases in BEC proliferation at 15 and 24 hours after biliary obstruction compared with adenovirus control. Our results showed that HNF-6 expression is diminished in BEC and hepatocytes and that maintaining hepatic HNF-6 expression hinders the normal biliary proliferative response to bile duct injury. This suggests that diminished hepatic HNF-6 levels are required for repair in response to biliary injury and that it regulates expression of genes that possess differentiation-specific function that are inhibitory to proliferation. In conclusion, we propose a biologic role for diminished HNF-6 protein levels in bile duct disease.

Adenovirus-mediated increase in HNF-3beta or HNF-3alpha shows differences in levels of liver glycogen and gene expression

We previously generated a transgenic mouse line (T-77) in which increased hepatic expression of the hepatocyte nuclear factor-3beta (HNF-3beta) protein was used to assess its role in hepatocyte-specific gene transcription. The T-77 transgenic mice displayed elevated serum bile acid and bilirubin levels and a complete absence of hepatic glycogen storage. These postnatal liver defects were associated with diminished expression of hepatocyte genes involved in gluconeogenesis and bile acid transport as well as reduced levels of hepatocyte transcription factors. In this study, we show that mouse tail vein injections of adenovirus expressing the rat HNF-3beta (AdHNF3beta) cDNA efficiently increased its levels throughout the liver lobule and recapitulated the T-77 transgenic liver phenotype within several days postinfection. Likewise, the AdHNF3beta-infected liver phenotype was associated with reduced hepatic expression of genes involved in glucose homeostasis, bile acid transport, and bilirubin conjugation, which were not found with control adenovirus infections. These studies show that adenovirus-mediated gene transfer is an effective method for rapid hepatic increases in transcription factor levels to determine in vivo target genes. In contrast, AdHNF3alpha-infected liver displayed only a transient reduction in hepatic glycogen levels and was associated with less severe decreases in hepatic expression of gluconeogenic and bilirubin metabolism genes. Consistent with these findings, only T-77 transgenic and AdHNF3beta-infected liver exhibited diminished hepatic expression of the HNF-6 transcription factor, suggesting that reduced HNF-6 levels contribute to diminished HNF-3beta-specific transcriptional activity.

Defects in pulmonary vasculature and perinatal lung hemorrhage in mice heterozygous null for the Forkhead Box f1 transcription factor

Decreased pulmonary expression of Forkhead Box f1 (Foxf1) transcription factor was associated with lethal alveolar hemorrhage in 55% of the Foxf1 +/- newborn mice. The severity of the pulmonary abnormalities correlates with the levels of Foxf1 mRNA. Defects in alveolarization and vasculogenesis were observed in subsets of the Foxf1 +/- mice with relatively low levels of expression from the normal Foxf1 allele. Lung hemorrhage was coincident with disruption of the mesenchymal-epithelial cell interfaces in the alveolar and bronchiolar regions of the lung parenchyma and was associated with increased apoptosis and reduced surfactant protein B (SP-B) expression. Finally, the lung defect associated with the Foxf1 +/- mutation was accompanied by reduced expression of vascular endothelial growth factor (VEGF), the VEGF receptor 2 (Flk-1), bone morphogenetic protein 4 (Bmp-4), and the transcription factors of the Brachyury T-Box family (Tbx2-Tbx5) and Lung Kruppel-like Factor. Reduction in the level of Foxf1 caused neonatal pulmonary hemorrhage and abnormalities in alveologenesis, implicating this transcription factor in the regulation of mesenchyme-epithelial interaction critical for lung morphogenesis.

Atypical mouse cerebellar development is caused by ectopic expression of the forkhead box transcription factor HNF-3beta

To assess the role of hepatocyte nuclear factor-3beta (HNF-3beta) in hepatocyte-specific gene transcription, we reported the characterization of the liver phenotype with transgenic mice in which the -3-kb transthyretin (TTR) promoter functioned to increase HNF-3beta expression. During breeding of the TTR-HNF-3beta transgenic mice we noticed that they displayed severe ataxia. In this study, we describe the analysis of our transgenic cerebellar phenotype and demonstrate that ectopic expression of HNF-3beta disrupted cerebellar morphogenesis and caused reduction in cerebellar size. In postnatal cerebellum, the HNF-3beta transgene expression pattern is colocalized to glial fibrillary acidic protein-positive cerebellar astrocytes and Bergmann glial cells. As a result of protracted expression, the transgenic cerebella are impaired in terms of astrocyte dispersal and formation of Bergmann glial cell processes. This caused a disruption in neuronal cell migration to the cortical laminar layers and Purkinje dendritic arbor maturation, thus leading to diminished foliation. Differential hybridization of cDNA arrays was used to identify altered expression of cerebellar genes, which is consistent with the observed defect in transgenic cerebellar morphogenesis and size as well as glial maturation. These include diminished expression of the brain lipid-binding protein, which is required for glial morphological differentiation, and the basic helix-loop-helix NeuroD/Beta2 and homeodomain Engrailed-2 transcription factors, which are required for normal cerebellar morphogenesis and foliation. Undetectable levels of ataxia telangiectasia (ATM), which is required for proper development of the Purkinje dendritic arbor, were found in postnatal transgenic cerebella. Furthermore, the transgenic cerebella displayed levels of insulin-like growth factor binding protein-1 elevated to 22 times greater than those measured for wild-type cerebella, an elevation consistent with the reduction in transgenic cerebellar size.

The murine Pes1 gene encodes a nuclear protein containing a BRCT domain

Pescadillo was originally identified in the zebrafish Danio rerio as a site of a retrovirus-insertion mutation that caused severe defects during embryogenesis. In particular, growth of the fetal zebrafish liver was significantly affected by loss of pescadillo function. To begin to understand the role of pescadillo during mammalian hepatogenesis we identified the murine homologue of pescadillo and named it Pes1. A single gene localized to chromosome 11 on the mouse genome encodes Pes1. Although Pes1 mRNA was detected in all tissues examined it was present at the highest levels in both adult and fetal liver. Analysis of the predicted amino acid sequence of Pes1 found it to contain a BRCT domain, which has previously been found in several proteins involved in cell-cycle checkpoints and DNA repair. Consistent with a putative role in these processes we found that when recombinant Pes1 protein was expressed in HepG2 cells it localized to the nucleus.

Identification of differentially expressed genes in epithelial stem/progenitor cells of fetal rat liver

Differentially expressed cDNA clones from fetal rat liver were isolated using suppression subtractive hybridization, combined with an efficient screening strategy. Approximately 30,000 clones were screened, yielding 643 genes whose expression was induced, of which 201 clones were distinct and 68 represented ESTs or newly discovered genes of unknown function. Based on their expression patterns in different organs, fetal liver, liver regeneration models, and gut epithelial progenitor cell lines, the subtracted clones presented in this work were placed into four categories: (1) hepatoblast-specific genes; (2) hematopoietic cell-specific genes; (3) genes expressed in hepatoblasts, in hematopoietic cells, and at varying levels in other tissues; and (4) genes overexpressed in fetal liver, in models of activation of liver progenitor cells, and in epithelial progenitor cell lines. Hepatoblast-specific clones and those representing genes induced during liver regeneration are under further study to define their specific function(s) in liver cell growth control and/or differentiation.

Proliferation and differentiation of fetal liver epithelial progenitor cells after transplantation into adult rat liver

To identify cells that have the ability to proliferate and differentiate into all epithelial components of the liver lobule, we isolated fetal liver epithelial cells (FLEC) from ED 14 Fischer (F) 344 rats and transplanted these cells in conjunction with two-thirds partial hepatectomy into the liver of normal and retrorsine (Rs) treated syngeneic dipeptidyl peptidase IV mutant (DPPIV(-)) F344 rats. Using dual label immunohistochemistry/in situ hybridization, three subpopulations of FLEC were identified: cells expressing both alpha-fetoprotein (AFP) and albumin, but not CK-19; cells expressing CK-19, but not AFP or albumin, and cells expressing AFP, albumin, and cytokeratins-19 (CK-19). Proliferation, differentiation, and expansion of transplanted FLEC differed significantly in the two models. In normal liver, 1 to 2 weeks after transplantation, mainly cells with a single phenotype, hepatocytic (expressing AFP and albumin) or bile ductular (expressing only CK-19), had proliferated. In Rs-treated rats, in which the proliferative capacity of endogenous hepatocytes is impaired, transplanted cells showed mainly a dual phenotype (expressing both AFP/albumin and CK-19). One month after transplantation, DPPIV(+) FLEC engrafted into the parenchyma exhibited an hepatocytic phenotype and generated new hepatic cord structures. FLEC, localized in the vicinity of bile ducts, exhibited a biliary epithelial phenotype and formed new bile duct structures or were incorporated into pre-existing bile ducts. In the absence of a proliferative stimulus, ED 14 FLEC did not proliferate or differentiate. Our results demonstrate that 14-day fetal liver contains lineage committed (unipotential) and uncommitted (bipotential) progenitor cells exerting different repopulating capacities, which are affected by the proliferative status of the recipient liver and the host site within the liver where the transplanted cells become engrafted. These findings have important implications in future studies directed toward liver repopulation and ex vivo gene therapy.

Mammalian hepatocyte differentiation requires the transcription factor HNF-4α

HNF-4α is a transcription factor of the nuclear hormone receptor family that is expressed in the hepatic diverticulum at the onset of liver development. Mouse embryos lacking HNF-4α fail to complete gastrulation due to dysfunction of the visceral endoderm. This early embryonic lethality has so far prevented any analyses of the contribution of HNF-4α toward liver development and hepatocyte differentiation. However, we have shown that complementation ofHNF-4 α−/−embryos with a tetraploid embryo-derived wild-type visceral endoderm rescues this early developmental arrest and allowsHNF-4 α−/−embryos to proceed normally through midgestation stages of development. Examination of these rescued embryos revealed that HNF-4α was dispensable for specification and early development of the liver. However,HNF-4α−/− fetal livers failed to express a large array of genes whose expression in differentiated hepatocytes is essential for a functional hepatic parenchyma, including genes encoding several apolipoproteins, metabolic proteins, and serum factors. In addition, we have demonstrated that HNF-4α is essential for expression of the transcription factors HNF-1α and PXR within the fetal liver. We therefore conclude that HNF-4α is both essential for hepatocyte differentiation during mammalian liver development and also crucial for metabolic regulation and liver function.

Premature expression of the winged helix transcription factor HFH-11B in regenerating mouse liver accelerates hepatocyte entry into S phase

Two-thirds partial hepatectomy (PH) induces differentiated cells in the liver remnant to proliferate and regenerate to its original size. The proliferation-specific HNF-3/fork head homolog-11B protein (HFH-11B; also known as Trident and Win) is a family member of the winged helix/fork head transcription factors and in regenerating liver its expression is reactivated prior to hepatocyte entry into DNA replication (S phase). To examine whether HFH-11B regulates hepatocyte proliferation during liver regeneration, we used the -3-kb transthyretin (TTR) promoter to create transgenic mice that displayed ectopic hepatocyte expression of HFH-11B. Liver regeneration studies with the TTR-HFH-11B mice demonstrate that its premature expression resulted in an 8-h acceleration in the onset of hepatocyte DNA replication and mitosis. This liver regeneration phenotype is associated with protracted expression of cyclin D1 and C/EBPbeta, which are involved in stimulating DNA replication and premature expression of M phase promoting cyclin B1 and cdc2. Consistent with the early hepatocyte entry into S phase, regenerating transgenic livers exhibited earlier expression of DNA repair genes (XRCC1, mHR21spA, and mHR23B). Furthermore, in nonregenerating transgenic livers, ectopic HFH-11B expression did not elicit abnormal hepatocyte proliferation, a finding consistent with the retention of the HFH-11B transgene protein in the cytoplasm. We found that nuclear translocation of the HFH-11B transgene protein requires mitogenic signalling induced by PH and that its premature availability in regenerating transgenic liver allowed nuclear translocation to occur 8 h earlier than in wild type.

The nuclear receptor fetoprotein transcription factor is coexpressed with its target gene HNF-3beta in the developing murine liver, intestine and pancreas

During organogenesis, the winged helix hepatocyte nuclear factor 3beta (HNF-3beta) protein participates in regulating gene transcription in the developing esophagus, trachea, liver, lung, pancreas, and intestine. Hepatoma cell transfection studies identified a critical HNF-3beta promoter factor, named UF2-H3beta, and here, we demonstrate that UF2-H3beta is identical to the fetoprotein transcription factor (FTF). In situ hybridization studies of mouse embryos demonstrate that FTF expression initiates in the foregut endoderm during liver and pancreatic morphogenesis (day 9) and that earlier expression of FTF is observed in the yolk sac endoderm, branchial arch and neural crest cells (day 8). Abundant FTF hybridization signals are observed throughout morphogenesis of the liver, pancreas, and intestine and its expression continues in the epithelial cells of these adult organs. In day 17 mouse embryos and adult pancreas, however, expression of FTF becomes restricted to the exocrine acinar and ductal epithelial cells.