vHNF1 is expressed in epithelial cells of distinct embryonic origin during development and precedes HNF1 expression

Gene expression in the liver of the hagfish (Eptatretus burgeri) belonging to the Cyclostomata is ancestral to that of mammals

Although the liver of the hagfish, an earliest diverged lineage among vertebrates, has a histological architecture similar to that of mammals, its gene expression has not been explored yet. The present study was undertaken to comparatively characterize gene expression in the liver of the hagfish with that of the mouse, using in situ hybridization technique. Expression of alb (albumin) was detectable in all hepatocytes of the hagfish liver, but was negative in intrahepatic bile ducts. Their expression in abundant periportal ductules was weak. The expression pattern basically resembled that in mammalian livers, indicating that the differential expression of hepatocyte markers in hepatocytes and biliary cells may have been acquired in ancestral vertebrates. alb expression was almost homogeneous in the hagfish liver, whereas that in the mouse liver lobule was zonal. The glul (glutamate-ammonia ligase) expression was also homogeneously detectable in hepatocytes without zonation, and weakly so in biliary cells of the hagfish, which contrasted with its restricted pericentral expression in mouse livers. These findings indicated that the hagfish liver did not have mammalian-type zonation. Whereas tetrapods had Hnf (hepatocyte nuclear factor) 1a and Hnf1b genes encoding the transcription factors, the hagfish had a single gene of their orthologue hnf1. Although HNF1α and HNF1β were immunohistochemically detected in hepatocytes and biliary cells of the mouse, respectively, hnf1 was expressed in both hepatocytes and biliary cells of the hagfish. These data indicate that gene expression of hnf1 in the hagfish liver may be ancestral with that of alb and glul during vertebrate evolution.

Hepatocyte nuclear factor 1B mutation in a Chinese family with renal cysts and diabetes syndrome: A case report

BACKGROUND

Renal cysts and diabetes (RCAD) syndrome is an autosomal dominant diabetic renal disease. Precise molecular diagnosis of RCAD syndrome has proven valuable for understanding its mechanism and personalized therapy.

CASE SUMMARY

A RCAD patient and her family were studied to investigate potential responsible genes by the whole exome sequencing (WES). Candidate pathogenic variants were validated by Sanger sequencing. The clinical characteristics of RCAD patient were collected from medical records. Unlike those typical RCAD patients, we observed renal manifestation and prediabetes phenotype, but not reproductive organ phenotype and hypomagnesaemia. A novel 7-bp deletion mutation in exon 4 of the hepatocyte nuclear factor 1B, NM_000458: c.882_888del (p.V294fs), was identified by WES and confirmed by Sanger sequencing.

CONCLUSION

This novel mutation identified in a Chinese family with RCAD syndrome might be the molecular pathogenic basis of this disorder.

Transcription Control of Liver Development

During liver organogenesis, cellular transcriptional profiles are constantly reshaped by the action of hepatic transcriptional regulators, including FoxA1-3, GATA4/6, HNF1α/β, HNF4α, HNF6, OC-2, C/EBPα/β, Hex, and Prox1. These factors are crucial for the activation of hepatic genes that, in the context of compact chromatin, cannot access their targets. The initial opening of highly condensed chromatin is executed by a special class of transcription factors known as pioneer factors. They bind and destabilize highly condensed chromatin and facilitate access to other "non-pioneer" factors. The association of target genes with pioneer and non-pioneer transcription factors takes place long before gene activation. In this way, the underlying gene regulatory regions are marked for future activation. The process is called "bookmarking", which confers transcriptional competence on target genes. Developmental bookmarking is accompanied by a dynamic maturation process, which prepares the genomic loci for stable and efficient transcription. Stable hepatic expression profiles are maintained during development and adulthood by the constant availability of the main regulators. This is achieved by a self-sustaining regulatory network that is established by complex cross-regulatory interactions between the major regulators. This network gradually grows during liver development and provides an epigenetic memory mechanism for safeguarding the optimal expression of the regulators.

The Roles of Long Noncoding RNAs HNF1α-AS1 and HNF4α-AS1 in Drug Metabolism and Human Diseases

Long noncoding RNAs (lncRNAs) are RNAs with a length of over 200 nucleotides that do not have protein-coding abilities. Recent studies suggest that lncRNAs are highly involved in physiological functions and diseases. lncRNAs HNF1α-AS1 and HNF4α-AS1 are transcripts of lncRNA genes HNF1α-AS1 and HNF4α-AS1, which are antisense lncRNA genes located in the neighborhood regions of the transcription factor (TF) genes HNF1α and HNF4α, respectively. HNF1α-AS1 and HNF4α-AS1 have been reported to be involved in several important functions in human physiological activities and diseases. In the liver, HNF1α-AS1 and HNF4α-AS1 regulate the expression and function of several drug-metabolizing cytochrome P450 (P450) enzymes, which also further impact P450-mediated drug metabolism and drug toxicity. In addition, HNF1α-AS1 and HNF4α-AS1 also play important roles in the tumorigenesis, progression, invasion, and treatment outcome of several cancers. Through interacting with different molecules, including miRNAs and proteins, HNF1α-AS1 and HNF4α-AS1 can regulate their target genes in several different mechanisms including miRNA sponge, decoy, or scaffold. The purpose of the current review is to summarize the identified functions and mechanisms of HNF1α-AS1 and HNF4α-AS1 and to discuss the future directions of research of these two lncRNAs.

Hepatocyte nuclear factor-1β regulates Wnt signaling through genome-wide competition with β-catenin/lymphoid enhancer binding factor

Hepatocyte nuclear factor-1β (HNF-1β) is a tissue-specific transcription factor that is essential for normal kidney development and renal tubular function. Mutations of HNF-1β produce cystic kidney disease, a phenotype associated with deregulation of canonical (β-catenin-dependent) Wnt signaling. Here, we show that ablation of HNF-1β in mIMCD3 renal epithelial cells produces hyperresponsiveness to Wnt ligands and increases expression of Wnt target genes, including Axin2, Ccdc80, and Rnf43 Levels of β-catenin and expression of Wnt target genes are also increased in HNF-1β mutant mouse kidneys. Genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) in wild-type and mutant cells showed that ablation of HNF-1β increases by 6-fold the number of sites on chromatin that are occupied by β-catenin. Remarkably, 50% of the sites that are occupied by β-catenin in HNF-1β mutant cells colocalize with HNF-1β-occupied sites in wild-type cells, indicating widespread reciprocal binding. We found that the Wnt target genes Ccdc80 and Rnf43 contain a composite DNA element comprising a β-catenin/lymphoid enhancer binding factor (LEF) site overlapping with an HNF-1β half-site. HNF-1β and β-catenin/LEF compete for binding to this element, and thereby HNF-1β inhibits β-catenin-dependent transcription. Collectively, these studies reveal a mechanism whereby a transcription factor constrains canonical Wnt signaling through direct inhibition of β-catenin/LEF chromatin binding.

Prenatal diagnosis of HNF1B-associated renal cysts: Is there a need to differentiate intragenic variants from 17q12 microdeletion syndrome?

OBJECTIVE

17q12 microdeletions containing HNF1B and intragenic variants within this gene are associated with variable developmental, endocrine, and renal anomalies, often already noted prenatally as hyperechogenic/cystic kidneys. Here, we describe prenatal and postnatal phenotypes of seven individuals with HNF1B aberrations and compare their clinical and genetic data to those of previous studies.

METHODS

Prenatal sequencing and postnatal chromosomal microarray analysis were performed in seven individuals with renal and/or neurodevelopmental phenotypes. We evaluated HNF1B-related clinical features from 82 studies and reclassified 192 reported intragenic HNF1B variants.

RESULTS

In a prenatal case, we identified a novel in-frame deletion p.(Gly239del) within the HNF1B DNA-binding domain, a mutational hot spot as demonstrated by spatial clustering analysis and high computational prediction scores. The six postnatally diagnosed individuals harbored 17q12 microdeletions. Literature screening revealed variable reporting of HNF1B-associated clinical traits. Overall, both mutation groups showed a high phenotypic heterogeneity. The reclassification of all previously reported intragenic HNF1B variants provided an up-to-date overview of the mutational spectrum.

CONCLUSIONS

We highlight the value of prenatal HNF1B screening in renal developmental diseases. Standardized clinical reporting and systematic classification of HNF1B variants are necessary for a more accurate risk quantification of prenatal and postnatal clinical features, improving genetic counseling and prenatal decision making.

New insights into the role of HNF-1β in kidney (patho)physiology

Hepatocyte nuclear factor-1β (HNF-1β) is an essential transcription factor that regulates the development and function of epithelia in the kidney, liver, pancreas, and genitourinary tract. Humans who carry HNF1B mutations develop heterogeneous renal abnormalities, including multicystic dysplastic kidneys, glomerulocystic kidney disease, renal agenesis, renal hypoplasia, and renal interstitial fibrosis. In the embryonic kidney, HNF-1β is required for ureteric bud branching, initiation of nephrogenesis, and nephron segmentation. Ablation of mouse Hnf1b in nephron progenitors causes defective tubulogenesis, whereas later inactivation in elongating tubules leads to cyst formation due to downregulation of cystic disease genes, including Umod, Pkhd1, and Pkd2. In the adult kidney, HNF-1β controls the expression of genes required for intrarenal metabolism and solute transport by tubular epithelial cells. Tubular abnormalities observed in HNF-1β nephropathy include hyperuricemia with or without gout, hypokalemia, hypomagnesemia, and polyuria. Recent studies have identified novel post-transcriptional and post-translational regulatory mechanisms that control HNF-1β expression and activity, including the miRNA cluster miR17 ∼ 92 and the interacting proteins PCBD1 and zyxin. Further understanding of the molecular mechanisms upstream and downstream of HNF-1β may lead to the development of new therapeutic approaches in cystic kidney disease and other HNF1B-related renal diseases.

HNF1B nephropathy has a slow-progressive phenotype in childhood-with the exception of very early onset cases: results of the German Multicenter HNF1B Childhood Registry

BACKGROUND

HNF1B gene mutations are an important cause of bilateral (cystic) dysplasia in children, complicated by chronic renal insufficiency. The clinical variability, the absence of genotype-phenotype correlations, and limited long-term data render counseling of affected families difficult.

METHODS

Longitudinal data of 62 children probands with genetically proven HNF1B nephropathy was obtained in a multicenter approach. Genetic family cascade screening was performed in 30/62 cases.

RESULTS

Eighty-seven percent of patients had bilateral dysplasia, 74% visible bilateral, and 16% unilateral renal cysts at the end of observation. Cyst development was non-progressive in 72% with a mean glomerular filtration rate (GFR) loss of - 0.33 ml/min/1.73m² per year (± 8.9). In patients with an increase in cyst number, the annual GFR reduction was - 2.8 ml/min/1.73m² (± 13.2), in the total cohort - 1.0 ml/min/1.73m² (±10.3). A subset of HNF1B patients differs from this group and develops end stage renal disease (ESRD) at very early ages < 2 years. Hyperuricemia (37%) was a frequent finding at young age (median 1 year), whereas hypomagnesemia (24%), elevated liver enzymes (21%), and hyperglycemia (8%) showed an increased incidence in the teenaged child. Genetic analysis revealed no genotype-phenotype correlations but a significant parent-of-origin effect with a preponderance of 81% of maternal inheritance in dominant cases.

CONCLUSIONS

In most children, HNF1B nephropathy has a non-progressive course of cyst development and a slow-progressive course of kidney function. A subgroup of patients developed ESRD at very young age < 2 years requiring special medical attention. The parent-of-origin effect suggests an influence of epigenetic modifiers in HNF1B disease.

Role of HNF1β in the differential diagnosis of yolk sac tumor from other germ cell tumors

Identification of the yolk sac tumor (YST) component in germ cell tumors (GCT) may prove challenging, and highly sensitive and specific immunohistochemical markers are still lacking. Preliminary data from the literature suggest that HNF1β may represent a sensitive marker of YST. The specificity of HNF1β has not been addressed in GCT. A cohort of 49 YST specimens from 45 patients was designed, occurring either as pure tumors, or as a component of a mixed GCT. Immunohistochemistry was conducted on whole tumor sections using HNF1β. SALL4, OCT4, CD30, CDX2, Cytokeratin 19, Glypican 3, and GATA3 were used for classification of the GCT components. Patients were mostly male (39/45), aged 14 months to 49 years, with primary testicular tumors (37/39), or primary mediastinal pure YSTs (2/39). All 6 primary tumors occurring in females (6/45) were pure ovarian YSTs; age range was 4 to 72 years. HNF1β nuclear reactivity was seen in the YST component in all 49 tumors, with a moderate to strong nuclear pattern of staining. Embryonal carcinoma (EC, 0/32) and seminoma (0/6) were negative. Choriocarcinoma (6/6) showed faint focal cytoplasmic reactivity to HNF1β but no nuclear staining. In teratomas, only enteric-type glands showed nuclear reactivity to HNF1β (11/16). Therefore, HNF1β sensitivity in YST component identification was 100% and specificity was 80%. Thus, in our experience, HNF1β is a sensitive and reliable marker of the YST component in GCT, and allows distinction of YST from intricately admixed EC, especially in the diffuse embryoma pattern.

The molecular functions of hepatocyte nuclear factors - In and beyond the liver

The hepatocyte nuclear factors (HNFs) namely HNF1α/β, FOXA1/2/3, HNF4α/γ and ONECUT1/2 are expressed in a variety of tissues and organs, including the liver, pancreas and kidney. The spatial and temporal manner of HNF expression regulates embryonic development and subsequently the development of multiple tissues during adulthood. Though the HNFs were initially identified individually based on their roles in the liver, numerous studies have now revealed that the HNFs cross-regulate one another and exhibit synergistic relationships in the regulation of tissue development and function. The complex HNF transcriptional regulatory networks have largely been elucidated in rodent models, but less so in human biological systems. Several heterozygous mutations in these HNFs were found to cause diseases in humans but not in rodents, suggesting clear species-specific differences in mutational mechanisms that remain to be uncovered. In this review, we compare and contrast the expression patterns of the HNFs, the HNF cross-regulatory networks and how these liver-enriched transcription factors serve multiple functions in the liver and beyond, extending our focus to the pancreas and kidney. We also summarise the insights gained from both human and rodent studies of mutations in several HNFs that are known to lead to different disease conditions.

Early Developmental Perturbations in a Human Stem Cell Model of MODY5/HNF1B Pancreatic Hypoplasia

Patients with an HNF1B^S148L/+ mutation (MODY5) typically exhibit pancreatic hypoplasia. However, the molecular mechanisms are unknown due to inaccessibility of patient material and because mouse models do not fully recapitulate MODY5. Here, we differentiated MODY5 human-induced pluripotent stem cells (hiPSCs) into pancreatic progenitors, and show that the HNF1B^S148L/+ mutation causes a compensatory increase in several pancreatic transcription factors, and surprisingly, a decrease in PAX6 pancreatic gene expression. The lack of suppression of PDX1, PTF1A, GATA4, and GATA6 indicates that MODY5-mediated pancreatic hypoplasia is mechanistically independent. Overexpression studies demonstrate that a compensatory increase in PDX1 gene expression is due to mutant HNF1B^S148L/+ but not wild-type HNF1B or HNF1A. Furthermore, HNF1B does not appear to directly regulate PAX6 gene expression necessary for glucose tolerance. Our results demonstrate compensatory mechanisms in the pancreatic transcription factor network due to mutant HNF1B^S148L/+ protein. Thus, patients typically develop MODY5 but not neonatal diabetes despite exhibiting pancreatic hypoplasia.

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HNF1B^S148L/+ mutation elicits a compensatory increase in DE and pancreatic genes

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MODY5-mediated pancreatic hypoplasia is independent of PDX1, PTF1A, GATA4, and GATA6

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HNF1B^S148L mutation directly causes a compensatory increase in PDX1 gene expression

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HNF1B^S148L/+ mutation limits PAX6 expression and consequently leads to MODY5

Transcription Factor Hepatocyte Nuclear Factor-1β (HNF-1β) Regulates MicroRNA-200 Expression through a Long Noncoding RNA

The transcription factor hepatocyte nuclear factor-1β (HNF-1β) regulates tissue-specific gene expression in the kidney and other epithelial organs. Mutations of HNF-1β produce kidney cysts, and previous studies have shown that HNF-1β regulates the transcription of cystic disease genes, including Pkd2 and Pkhd1. Here, we combined chromatin immunoprecipitation and next-generation sequencing (ChIP-Seq) with microarray analysis to identify microRNAs (miRNAs) that are directly regulated by HNF-1β in renal epithelial cells. These studies identified members of the epithelial-specific miR-200 family (miR-200b/200a/429) as novel transcriptional targets of HNF-1β. HNF-1β binds to two evolutionarily conserved sites located 28 kb upstream to miR-200b. Luciferase reporter assays showed that the HNF-1β binding sites were located within a promoter that was active in renal epithelial cells. Mutations of the HNF-1β binding sites abolished promoter activity. RT-PCR analysis revealed that a long noncoding RNA (lncRNA) is transcribed from the promoter and encodes the miR-200 cluster. Inhibition of the lncRNA with siRNAs decreased the levels of miR-200 but did not affect expression of the Ttll10 host gene. The expression of the lncRNA and miR-200 was decreased in kidneys from HNF-1β knock-out mice and renal epithelial cells expressing dominant-negative mutant HNF-1β. The expression of miR-200 targets, Zeb2 and Pkd1, was increased in HNF-1β knock-out kidneys and in cells expressing mutant HNF-1β. Overexpression of miR-200 decreased the expression of Zeb2 and Pkd1 in HNF-1β mutant cells. These studies reveal a novel pathway whereby HNF-1β directly contributes to the control of miRNAs that are involved in epithelial-mesenchymal transition and cystic kidney disease.

Hepatocyte nuclear factor-1β: A regulator of kidney development and cystogenesis

The understanding of the genomics of the renal tissue has gathered a considerable interest and is making rapid progress. The molecular mechanisms as well as the precise function of the associated molecular components toward renal pathophysiology have recently been realized. For the cystic kidney disease, the regulation of gene expression affecting epithelial cells proliferation, apoptosis as well as process of differentiation/de-differentiation represent key molecular targets. For the cystic disorders, molecular targets have been identified, which besides lending heterogeneity to cysts may also provide tools to unravel their functional importance to understand the renal tissue homeostasis. This review focuses on providing comprehensive information about the transcriptional regulatory role of hepatocyte nuclear factor-1β, a homeoprotein, as well as its interacting partners in renal tissue development and pathophysiology.

Transcriptional control of hepatocyte differentiation

The liver is the largest glandular organ in the body and plays a central role in controlling metabolism. During hepatogenesis, complex developmental processes must generate an array of cell types that are spatially arranged to generate a hepatic architecture that is essential to support liver function. The processes that control the ultimate formation of the liver are diverse and complex and in many cases poorly defined. Much of the focus of research during the past three decades has been on understanding how hepatocytes, which are the predominant liver parenchymal cells, differentiate during embryogenesis. Through a combination of mouse molecular genetics, embryology, and molecular biochemistry, investigators have defined a myriad of transcription factors that combine to control formation and function of hepatocytes. Here, we will review the major discoveries that underlie our current understanding of transcriptional regulation of hepatocyte differentiation.

Autophagy is a component of epithelial cell fate in obstructive uropathy

Epithelial cell fate and nephron loss in obstructive uropathy are not fully understood. We produced transgenic mice in which epithelial cells in the nephrons and collecting ducts were labeled with enhanced yellow fluorescent protein, and tracked the fate of these cells following unilateral ureteral obstruction (UUO). UUO led to a decrease in the number of enhanced yellow fluorescent protein-expressing cells and down-regulation of epithelial markers, E-cadherin, and hepatocyte nuclear factor-1beta. Following UUO, enhanced yellow fluorescent protein-positive cells were confined within the tubular basement membrane, were not found in the renal interstitium, and did not express alpha-smooth muscle actin or S100A4, markers of myofibroblasts and fibroblasts. Moreover, when proximal tubules were labeled with dextran before UUO, dextran-retaining cells did not migrate into the interstitium or express alpha-smooth muscle actin. These results indicate that UUO leads to tubular epithelial loss but does not cause epithelial-to-mesenchymal transition that has been shown by others to be responsible for nephron loss and interstitial fibrosis. For the first time, we found evidence of enhanced autophagy in obstructed tubules, including accumulation of autophagosomes, increased expression of Beclin 1, and increased conversion of microtubular-associated protein 1 light chain 3-I to -II. Increased autophagy may represent a mechanism of tubular survival or may contribute to excessive cell death and tubular atrophy after obstructive injury.

Prospero-related homeobox protein (Prox1) inhibits hepatitis B virus replication through repressing multiple cis regulatory elements

Hepatitis B virus (HBV) gene transcription is controlled by viral promoters and enhancers, the activities of which are regulated by a number of cellular factors as well as virally encoded proteins. Negative regulation of HBV cis-element activities by cellular factors has been reported less widely than their activation. In this study, we report that nuclear factor Prospero-related homeobox protein (Prox1) represses HBV antigen expression and genome replication in cultured hepatocytes. By using reporter-gene analysis, three of the four HBV promoters, namely the enhancer II/core promoter (ENII/Cp), preS1 promoter (Sp1) and enhancer I/X promoter, were identified as targets for Prox1-mediated repression. Mechanistic analysis then revealed that, for ENII/Cp, Prox1 serves as a corepressor of liver receptor homologue 1 (LRH-1) and downregulates LRH-1-mediated activation of ENII/Cp, whereas for Sp1, Prox1 partially represses Sp1 activity by interacting directly with hepatocyte nuclear factor 1. Identification of Prox1 as an HBV repressor will help in the understanding of detailed interactions between viral cis elements and host cellular factors and may also form the basis for new anti-HBV intervention therapeutics.

HNF-1beta regulates transcription of the PKD modifier gene Kif12

Hepatocyte nuclear factor-1beta (HNF-1beta) is a transcription factor that regulates gene expression in the kidney, liver, pancreas, and other epithelial organs. Mutations of HNF-1beta lead to a syndrome of inherited renal cysts and diabetes and are also a common cause of sporadic renal dysplasia. The full complement of target genes responsible for the functions of HNF-1beta, however, is incompletely defined. Using a functional genomics approach involving chromatin immunoprecipitation and promoter arrays, combined with gene expression profiling, we found that an HNF-1beta target gene in the kidney is kinesin family member 12 (Kif12), a gene previously identified as a candidate modifier gene in the cpk mouse model of polycystic kidney disease. Mutations of HNF-1beta inhibited Kif12 transcription in both cultured cells and knockout mice by altering co-factor recruitment and histone modification. Because kinesin-12 family members participate in orienting cell division, downregulation of Kif12 may underlie the abnormal planar cell polarity observed in cystic kidney diseases.

Tissue-specific transcription factors in progression of epithelial tumors

Dedifferentiation and epithelial-mesenchymal transition are important steps in epithelial tumor progression. A central role in the control of functional and morphological properties of different cell types is attributed to tissue-specific transcription factors which form regulatory cascades that define specification and differentiation of epithelial cells during embryonic development. The main principles of the action of such regulatory systems are reviewed on an example of a network of hepatocyte nuclear factors (HNFs) which play a key role in establishment and maintenance of hepatocytes--the major functional type of liver cells. HNFs, described as proteins binding to promoters of most hepatospecific genes, not only control expression of functional liver genes, but are also involved in regulation of proliferation, morphogenesis, and detoxification processes. One of the central components of the hepatospecific regulatory network is nuclear receptor HNF4alpha. Derangement of the expression of this gene is associated with progression of rodent and human hepatocellular carcinomas (HCCs) and contributes to increase of proliferation, loss of epithelial morphology, and dedifferentiation. Dysfunction of HNF4alpha during HCC progression can be either caused by structural changes of this gene or occurs due to modification of up-stream regulatory signaling pathways. Investigations preformed on a model system of the mouse one-step HCC progression have shown that the restoration of HNF4alpha function in dedifferentiated cells causes partial reversion of malignant phenotype both in vitro and in vivo. Derangement of HNFs function was also described in other tumors of epithelial origin. We suppose that tissue-specific factors that underlie the key steps in differentiation programs of certain tissues and are able to receive or modulate signals from the cell environment might be considered as promising candidates for the role of tumor suppressors in the tissue types where they normally play the most significant role.

Transcription factor HNF and hepatocyte differentiation

To know the precise mechanisms underlying the life or death and the regeneration or differentiation of cells would be relevant and useful for the development of a regenerative therapy for organ failure. Liver-specific gene expression is controlled primarily at a transcriptional level. Studies on the transcriptional regulatory elements of genes expressed in hepatocytes have identified several liver-enriched transcriptional factors, including hepatocyte nuclear factor (HNF)-1, HNF-3, HNF-4, HNF-6 and CCAAT/enhancer binding protein families, which are key components of the differentiation process for the fully functional liver. The transcriptional regulation by these HNFs, which form a hierarchical and cooperative network, is both essential for hepatocyte differentiation during mammalian liver development and also crucial for metabolic regulation and liver function. Among these liver-enriched transcription factors, HNF-4 is likely to act the furthest upstream as a master gene in transcriptional cascade and interacts with other liver-enriched transcriptional factors to stimulate hepatocyte-specific gene transcription. A link between the extracellular matrix, changes in cytoskeletal filament assembly and hepatocyte differentiation via HNF-4 has been shown to be involved in the transcriptional regulation of liver-specific gene expression. This review provides an overview of the roles of liver-enriched transcription factors in liver function.

Role of HNF-1α and HNF-1β on insulin, IGF-1 and other potential target genes

Hepatocyte nuclear factor (HNF)-1α and HNF-1β are transcription factors that regulate many target genes in various tissues including liver, pancreas and kidney. Heterozygous mutations in the HNF-1α and HNF-1β genes result in maturity-onset diabetes of the young (MODY)3 and MODY5, respectively. The discovery of these 'hepatocyte nuclear factors' as MODY-responsible genes provided a breakthrough in the field of diabetes. Patients with HNF-1α and HNF-1β mutations, as well as their model mice, show impaired pancreatic β-cell function. The mechanism of impaired β-cell function and the target genes has been intensively investigated by considerable in vitro and in vivo studies. The insulin gene is one of the target genes of HNF-1α and HNF-1β in the β-cells, and may contribute to the diabetes. The IGF-1 gene is also regulated by HNF-1α and HNF-1β, and its decreased expression may contribute to growth failure and impaired β-cell proliferation. Mutations in HNF-1β result in symptoms in multiple organs, including kidney and liver, and several target genes have been reported to be involved in the pathogenesis. HNF-1α and HNF-1β may be one of the master regulators of hepatocyte and islet transcription, and further investigations by microarray and genome-scale analyses are providing information for the better understanding of the complex transcriptional network involving HNF-1α and -1β.

Function of HNF1 in the pathogenesis of diabetes

The importance of hepatocyte nuclear factors (HNFs), as well as other transcription factors in β-cell development and function, was underlined by the characterization of human mutations causing maturity-onset diabetes of the young (MODY). HNF1A and HNF1B mutations lead to MODY forms 3 and 5, respectively. Thus, transcriptional control is an essential mechanism underlying the precise metabolic control exerted by β-cells in regulating insulin release. The diabetes phenotype of MODY3 (HNF1α) and the phenotypes of MODY5 (HNF1β), which can also include renal disease and genitourinary malformations, as well as neonatal diabetes and pancreatic agenesis, have now been described. However, detailed molecular pathology remains elusive. The large array of dominant-negative and deletion mutations, and the lack of structure-phenotype relationships for most mutations, have not helped us to formulate a mechanistic understanding. Further molecular studies of HNF1 actions and gene regulation are anticipated to provide useful insights into β-cell biology and potential therapeutic tools.

Hepatocyte nuclear factor 1 and hypertensive nephropathy

Hypertension in spontaneously hypertensive rat (SHR) is associated with renal redox stress, and we hypothesized that nephropathy arises in SHR-A3 from altered capacity to mitigate redox stress compared with nephropathy-resistant SHR lines. We measured renal expression of redox genes in distinct lines of the spontaneously hypertensive rat (SHR-A3, SHR-B2, SHR-C) and the normotensive Wistar-Kyoto (WKY) strain. The SHR lines differ in either resisting (SHR-B2, SHR-C) or experiencing hypertensive nephropathy (SHR-A3). Immediately before the emergence of hypertensive renal injury expression of redox genes in SHR-A3 was profoundly altered compared with the injury-resistant SHR lines and WKY. This change appeared to arise in antioxidant genes where 16 of 28 were expressed at 34.3% of the level in the reference strain (WKY). No such change was observed in the injury-resistant SHR lines. We analyzed occurrence of transcription factor matrices in the promoters of the downregulated antioxidant genes. In these genes, the hepatocyte nuclear factor 1 (HNF1) transcription factor matrix was found to be nearly twice as likely to be present and the overall frequency of HNF1 sites was nearly 5 times higher, compared with HNF1 transcription factor matrices in antioxidant genes that were not downregulated. We identified 35 other (nonredox) renal genes regulated by HNF1. These were also significantly downregulated in SHR-A3, but not in SHR-B2 or SHR-C. Finally, expression of genes that comprise HNF1 (Tcf1, Tcf2, and Dcoh) was also downregulated in SHR-A3. The present experiments uncover a major change in transcriptional control by HNF1 that affects redox and other genes and precedes emergence of hypertensive renal injury.

Direct regulation of vHnf1 by retinoic acid signaling and MAF-related factors in the neural tube

The homeodomain transcription factor vHNF1 plays an essential role in the patterning of the caudal segmented hindbrain, where it participates in the definition of the boundary between rhombomeres (r) 4 and 5 and in the specification of the identity of r5 and r6. Understanding the molecular basis of vHnf1 own expression therefore constitutes an important issue to decipher the regulatory network governing hindbrain patterning. We have identified a highly conserved 800-bp enhancer element located in the fourth intron of vHnf1 and whose activity recapitulates vHnf1 neural expression in transgenic mice. Functional analysis of this enhancer revealed that it contains two types of essential motifs, a retinoic acid response element and two half T-MARE sites, indicating that it integrates direct inputs from the retinoic acid signaling cascade and MAF-related factors. Our data suggest that MAFB, which is itself regulated by vHNF1, acts as a positive modulator of vHnf1 in r5 and r6, whereas another MAF-related factor is absolutely required for the expression of vHnf1 in both the hindbrain and the spinal cord. We propose a model accounting for the initiation and maintenance phases of vHnf1 expression and for the establishment of the r4/r5 boundary, based on cooperative contributions of Maf factors and retinoic acid signaling.

Functional analysis on the 5'-flanking region of human FXR gene in HepG2 cells

The farnesoid X receptor (FXR) is a bile acid (BA)-activated nuclear receptor that plays a major role in the regulation of BA and lipid metabolism. Although modulation of FXR expression has been reported, the mechanisms underlying the regulation of human FXR are yet unclear. Functional assays showed that the -150/+29 nucleotides region from the first nucleotide at the Exon I is the minimal promoter of the human FXR gene by the technique of serial deletion and point mutants of the 5'-flanking region. Chromatin immunoprecipitation analysis and electrophoretic mobility shift assay revealed that hepatic nuclear factor 1alpha (HNF1alpha) interacted with the region. Co-transfection of the promoter with HNF1alpha expression vectors enhanced promoter activity of FXR gene. Over-expression of HNF1alpha up-regulated FXR expression in HepG2 cells. These data indicate that (a) the identified HNF1alpha binding site serves as a positive regulatory sequence, (b) the binding site is functionally active both in vivo and in vitro, and (c) the transcription factor HNF1alpha that binds to this site plays an important role in the regulation of human FXR promoter activity.

Chromatin remodeling agent trichostatin A: a key-factor in the hepatic differentiation of human mesenchymal stem cells derived of adult bone marrow

Background

The capability of human mesenchymal stem cells (hMSC) derived of adult bone marrow to undergo in vitro hepatic differentiation was investigated.

Results

Exposure of hMSC to a cocktail of hepatogenic factors [(fibroblast growth factor-4 (FGF-4), hepatocyte growth factor (HGF), insulin-transferrin-sodium-selenite (ITS) and dexamethasone)] failed to induce hepatic differentiation. Sequential exposure to these factors (FGF-4, followed by HGF, followed by HGF+ITS+dexamethasone), however, resembling the order of secretion during liver embryogenesis, induced both glycogen-storage and cytokeratin (CK)18 expression. Additional exposure of the cells to trichostatin A (TSA) considerably improved endodermal differentiation, as evidenced by acquisition of an epithelial morphology, chronological expression of hepatic proteins, including hepatocyte-nuclear factor (HNF)-3β, alpha-fetoprotein (AFP), CK18, albumin (ALB), HNF1α, multidrug resistance-associated protein (MRP)2 and CCAAT-enhancer binding protein (C/EBP)α, and functional maturation, i.e. upregulated ALB secretion, urea production and inducible cytochrome P450 (CYP)-dependent activity.

Conclusion

hMSC are able to undergo mesenchymal-to-epithelial transition. TSA is hereby essential to promote differentiation of hMSC towards functional hepatocyte-like cells.

Hepatocyte nuclear factor-1 beta mutations cause neonatal diabetes and intrauterine growth retardation: support for a critical role of HNF-1beta in human pancreatic development

AIM

The transcription factor hepatocyte nuclear factor-1beta (HNF-1beta) is expressed in rodent pancreatic progenitor cells, where it is an important member of the genetic hierarchy that regulates the generation of pancreatic endocrine and exocrine cells. The recent description of an HNF-1beta mutation in a patient with neonatal diabetes suggests that HNF-1beta may also play a key role in human pancreatic B-cell development. We aimed to investigate the role of HNF-1beta mutations in neonatal diabetes and also the impact of HNF-1beta mutations on fetal growth.

METHODS

We sequenced the HNF-1beta gene in 27 patients with neonatal diabetes in whom other known genetic aetiologies had been excluded. Birth weight was investigated in 21 patients with HNF-1beta mutations.

RESULTS

A heterozygous HNF-1beta mutation, S148L, was identified in one patient with neonatal diabetes diagnosed at 17 days, which rapidly resolved only to relapse at 8 years. This patient had pancreatic atrophy, mild exocrine insufficiency and low birth weight (1.83 kg at 40 weeks' gestation). Intrauterine growth was markedly reduced in patients born to unaffected mothers with a median birth weight of 2.4 kg (range 1.8-3.3) (P = 0.006), median centile weight 3 (0.008-38), and 69% were small for gestational age.

CONCLUSION

HNF-1beta mutations are a rare cause of neonatal diabetes as well as pancreatic exocrine and endocrine dysfunction. Low birth weight is a common feature of patients with HNF-1beta mutations and is consistent with reduced insulin secretion in utero. These findings support a key role for HNF-1beta in early pancreatic progenitor cells in man.

Sequential exposure to cytokines reflecting embryogenesis: the key for in vitro differentiation of adult bone marrow stem cells into functional hepatocyte-like cells

Differentiation of adult bone marrow stem cells (BMSC) into hepatocyte-like cells is commonly performed by continuous exposure to a cytokines-cocktail. Here, it is shown that the differentiation efficacy in vitro can be considerably enhanced by sequential addition of liver-specific factors (fibroblast growth factor-4, hepatocyte growth factor, insulin-transferrin-sodium selenite, and dexamethasone) in a time-dependent order that closely resembles the secretion pattern during in vivo liver embryogenesis. Quantitative RT-PCR analysis and immunocytochemistry showed that, upon sequential exposure to liver-specific factors, different stages of hepatocyte differentiation, as seen during liver embryogenesis, can be mimicked. Indeed, expression of the early hepatocyte markers alpha-fetoprotein and hepatocyte nuclear factor (HNF)3beta decreased as differentiation progressed, whereas levels of the late liver-specific markers albumin (ALB), cytokeratin (CK)18, and HNF1alpha were gradually upregulated. In contrast, cocktail treatment did not significantly alter the expression pattern of the hepatic markers. Moreover, sequentially exposed cells featured highly differentiated hepatic functions, including ALB secretion, glycogen storage, urea production, and inducible cytochrome P450-dependent activity, far more efficiently compared to the cocktail condition. In conclusion, sequential induction of the differentiation process, analogous to in vivo liver development, is crucial for in vitro differentiation of adult rat BMSC into functional hepatocyte-like cells. This model may not only be applicable for in vitro studies of endoderm differentiation but it also provides a "virtually unlimited" source of functional hepatocytes, suitable for preclinical pharmacological research and testing, and cell and organ development.

Severe pancreas hypoplasia and multicystic renal dysplasia in two human fetuses carrying novel HNF1beta/MODY5 mutations

Heterozygous mutations in the HNF1beta/vHNF1/TCF2 gene cause maturity-onset diabetes of the young (MODY5), associated with severe renal disease and abnormal genital tract. Here, we characterize two fetuses, a 27-week male and a 31.5-week female, carrying novel mutations in exons 2 and 7 of HNF1beta, respectively. Although these mutations were predicted to have different functional consequences, both fetuses displayed highly similar phenotypes. They presented one of the most severe phenotypes described in HNF1beta carriers: bilateral enlarged polycystic kidneys, severe pancreas hypoplasia and abnormal genital tract. Consistent with this, we detected high levels of HNF1beta transcripts in 8-week human embryos in the mesonephros and metanephric kidney and in the epithelium of pancreas. Renal histology and immunohistochemistry analyses of mutant fetuses revealed cysts derived from all nephron segments with multilayered epithelia and dysplastic regions, accompanied by a marked increase in the expression of beta-catenin and E-cadherin. A significant proportion of cysts still expressed the cystic renal disease proteins, polycystin-1, polycystin-2, fibrocystin and uromodulin, implying that cyst formation may result from a deregulation of cell-cell adhesion and/or the Wnt/beta-catenin signaling pathway. Both fetuses exhibited a severe pancreatic hypoplasia with underdeveloped and disorganized acini, together with an absence of ventral pancreatic-derived tissue. beta-catenin and E-cadherin were strongly downregulated in the exocrine and endocrine compartments, and the islets lacked the transporter essential for glucose-sensing GLUT2, indicating a beta-cell maturation defect. This study provides evidence of differential gene-dosage requirements for HNF1beta in normal human kidney and pancreas differentiation and increases our understanding of the etiology of MODY5 disorder.

Embryoid body-mediated differentiation of mouse embryonic stem cells along a hepatocyte lineage: insights from gene expression profiles

Pluripotent embryonic stem (ES) cells represent a promising renewable cell source for the generation of functional differentiated cells. Previous studies incorporating embryoid body (EB)-mediated stem cell differentiation have, either spontaneously or after growth factor and extracellular matrix protein supplementation, yielded populations of hepatocyte lineage cells expressing mature hepatocyte markers such as albumin (ALB). In an effort to promote ES cell commitment to the hepatocyte lineage, we have evaluated the effects of four culture conditions on albumin and gene expression in differentiating ES cells. Quantitative in situ immunofluorescence and cDNA microarray analyses were used to describe not only lineage specificity but also to provide insights into the effects of disparate culture environments on the mechanisms of differentiation. The results of these studies suggest that spontaneous and collagen-mediated differentiation induce cells with the highest levels of ALB expression but mature liver specific genes were only expressed in the spontaneous condition. Further analysis of gene expression profiles indicated that two distinct mechanisms may govern spontaneous and collagen-mediated differentiation.

The vHNF1 homeodomain protein establishes early rhombomere identity by direct regulation of Kreisler expression

The early transcriptional hierarchy that subdivides the vertebrate hindbrain into seven to eight segments, the rhombomeres (r1-r8), is largely unknown. The Kreisler (MafB, Krml1, Val) gene is earliest gene expressed in an r5/r6-restricted manner and is essential for r5 and r6 development. We have identified the S5 regulatory element that directs early Kreisler expression in the future r5/r6 domain in 0-10 somite stage embryos. variant Hepatocyte Nuclear Factor 1 (vHNF1/HNF1beta/LF-3B) is transiently expressed in the r5/r6 domain of 0-10 somite stage embryos and a vHNF1binding site within this element is essential but not sufficient for r5/r6-specific expression. Thus, early inductive events that initiate Kreisler expression are clearly distinct from later-acting ones that modulate its expression levels. This site and some of the surrounding sequences are evolutionarily conserved in the genomic DNA upstream of the Kreisler gene among species as divergent as mouse, humans, and chickens. This provides the first evidence of a direct requirement for vHNF1 in initiation of Kreisler expression, suggests that the role of vHNF1 is evolutionarily conserved, and indicates that vHNF1 collaborates with other transcription factors, which independently bind to the S5 regulatory region, to establish the r5/r6 domain.

The position of premature termination codons in the hepatocyte nuclear factor -1 beta gene determines susceptibility to nonsense-mediated decay

The nonsense-mediated decay (NMD) pathway is an mRNA surveillance mechanism that detects and degrades transcripts containing premature termination codons. The position of a truncating mutation can govern the resulting phenotype as mutations in the last exon evade NMD. In this study we investigated the susceptibility to NMD of six truncating HNF-1beta mutations by allele-specific quantitative real-time PCR using transformed lymphoblastoid cell lines. Four of six mutations (R181X, Q243fsdelC, P328L329fsdelCCTCT and A373fsdel29) showed evidence of NMD with levels of mutant transcript at 71% (p=0.009), 24% (p=0.008), 22% (p=0.008) and 3% (p=0.016) of the wild-type allele respectively. Comparable results were derived from lymphoblastoid cells and renal tubule cells isolated from a patient's overnight urine confirming that cell lines provide a good model for mRNA analysis. Two mutations (H69fsdelAC and P159fsdelT) produced transcripts unexpectedly immune to NMD. We conclude that truncating mutant transcripts of the HNF-1beta gene do not conform to the known rules governing NMD susceptibility, but instead demonstrate a previously unreported 5' to 3' polarity. We hypothesise that this may be due to reinitiation of translation downstream of the premature termination codon. Our study suggests that reinitiation of translation may be an important mechanism in the evasion of NMD, but that other factors such as the distance from the native initiation codon may also play a part.

Control of ACAT2 liver expression by HNF1

ACAT catalyzes the formation of cholesteryl esters from cholesterol and long-chain fatty acids. There are two known genes encoding the two ACAT enzymes, ACAT1 and ACAT2 (also known as Soat1 and Soat2). In adult humans, ACAT1 is present in most tissues, whereas ACAT2 is localized to enterocytes and hepatocytes. In this report, we elucidate the mechanisms that control the liver-specific expression of the human ACAT2 gene. We identified hepatic nuclear factor 1 (HNF1) as an important liver-specific trans-acting element for the human ACAT2 gene using the human hepatocellular carcinoma cell lines HuH7 and HepG2. Targeted deletion of the HNF1 binding site in the DNA sequence abolished not only the basal promoter function in HepG2 and HuH7 cells but also the induction of the ACAT2 promoter by HNF1. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that the transcription factors HNF1alpha and HNF1beta interact with this region in the human ACAT2 gene in vitro and in vivo. These data indicate that a) the identified HNF1 binding site serves as a positive regulator sequence, b) the binding site is functionally active both in vivo and in vitro, and c) the transcription factors HNF1alpha and HNF1beta, which bind to this site, play an important part in the regulation of the human ACAT2 promoter.

Regulatory role of CCAAT/enhancer binding protein-beta in the production of plasma proteins in yolk sac tumor

Yolk sac tumor (endodermal sinus tumor) is a malignant germ cell tumor characterized by AFP production, in which histologic foci similar to hepatocellular carcinoma occasionally coexist. We assumed a possible contribution of CCAAT/enhancer binding protein (C/EBP)-beta, a transcription factor implicated in the regulation of plasma proteins in the liver, to the regulation of AFP production and to the expression of other plasma proteins in yolk sac tumor cells because our immunohistochemical analysis revealed nuclear expression of C/EBP-beta in human yolk sac tumors. Overexpression of C/EBP-beta in a rat yolk sac tumor cell line, AT-2-TC, increased production of AFP and other plasma proteins, including albumin, alpha-1-antitrypsin, hepatoglobin, and transferrin. Liver-enriched transcription factors, including hepatocyte nuclear factors (HNF)-1alpha, -1 beta, and -4, were also induced. The induction of this protein expression was only evident in xenografts, where C/EBP-beta was phosphorylated and the activating isoform of C/EBP-beta was relatively predominant. These results indicate that C/EBP-beta plays a role in the production of plasma proteins of yolk sac tumors.

Role of the Hepatocyte Nuclear Factor-1β (HNF-1β) C-terminal Domain in Pkhd1 (ARPKD) Gene Transcription and Renal Cystogenesis

Hepatocyte nuclear factor-1beta (HNF-1beta) is a homeodomain-containing transcription factor that regulates tissue-specific gene expression in the kidney and other epithelial organs. Mutations of HNF-1beta produce congenital cystic abnormalities of the kidney, and previous studies showed that HNF-1beta regulates the expression of the autosomal recessive polycystic kidney disease (ARPKD) gene, Pkhd1. Here we show that the C-terminal region of HNF-1beta contains an activation domain that is functional when fused to a heterologous DNA-binding domain. An HNF-1beta deletion mutant lacking the C-terminal domain interacts with wild-type HNF-1beta, binds DNA, and functions as a dominant-negative inhibitor of a chromosomally integrated Pkhd1 promoter. The activation of the Pkhd1 promoter by wild-type HNF-1beta is stimulated by sodium butyrate or coactivators CREB (cAMP-response element)-binding protein (CBP) and P/CAF. The interaction with CBP and P/CAF requires the C-terminal domain. Expression of an HNF-1beta C-terminal deletion mutant in transgenic mice produces renal cysts, increased cell proliferation, and dilatation of the ureter similar to mice with kidney-specific inactivation of HNF-1beta. Pkhd1 expression is inhibited in cystic collecting ducts but not in non-cystic proximal tubules, despite transgene expression in this nephron segment. We conclude that the C-terminal domain of HNF-1beta is required for the activation of the Pkhd1 promoter. Deletion mutants lacking the C-terminal domain function as dominant-negative mutants, possibly by preventing the recruitment of histone acetylases to the promoter. Cyst formation correlates with inhibition of Pkhd1 expression, which argues that mutations of HNF-1beta produce kidney cysts by down-regulating the ARPKD gene, Pkhd1. Expression of HNF-1alpha in proximal tubules may protect against cystogenesis.

The HNF1β transcription factor has several domains involved in nephrogenesis and partially rescues Pax8/lim1-induced kidney malformations

The tissue-specific transcription factors HNF1alpha and HNF1beta are closely related homeodomain proteins conserved in vertebrate evolution. Heterozygous mutations in human HNF1beta but not in HNF1alpha genes are associated with kidney malformations. Overexpression of HNF1beta in Xenopus embryos leads to defective pronephros development, while HNF1alpha has no effect. We have defined the regions responsible for this functional difference between HNF1beta and HNF1alpha in transfected HeLa cells as well as in injected Xenopus embryos. Using domain swapping experiments, we located a nuclear localization signal in the POUH domain of HNF1beta, and showed that the POUS and POUH domains of HNF1beta mediate a high transactivation potential in transfected cells. In injected Xenopus embryos three HNF1beta domains are involved in nephrogenesis. These include the dimerization domain, the 26 amino acid segment specific for splice variant A as well as the POUH domain. As HNF1beta together with Pax8 and lim1 constitute the earliest regulators in the pronephric anlage, it is possible that they cooperate during early nephrogenesis. We have shown here that HNF1beta can overcome the enlargement and the induction of an ectopic pronephros mediated by overexpression of Pax8 and lim1. However, the phenotype induced by Pax8 and lim1 overexpression and characterized by cyst-like structures and thickening of the pronephric tubules was not altered by HNF1beta overexpression. Taken together, HNF1beta acts antagonistically to Pax8 and lim1 in only some processes during nephrogenesis, and a simple antagonistic relationship does not completely describe the functions of these genes. We conclude that HNF1beta has some distinct morphogenetic properties during nephrogenesis.

Selective deletion of the Hnf1beta (MODY5) gene in beta-cells leads to altered gene expression and defective insulin release

Hepatocyte nuclear factor 1alpha (HNF1alpha) and HNF1beta (or vHNF1) are closely related transcription factors expressed in liver, kidney, gut, and pancreatic beta-cells. Many HNF1 target genes are involved in carbohydrate metabolism. Human mutations in HNF1alpha or HNF1beta lead to maturity-onset diabetes of the young (MODY3 and MODY5, respectively), and patients present with impaired glucose-stimulated insulin secretion. The underlying defect in MODY5 is not known. Analysis of HNF1beta deficiency in mice has not been possible because HNF1beta null mice die in utero. To examine the role of HNF1beta in glucose homeostasis, viable mice deleted for HNF1beta selectively in beta-cells (beta/H1beta-KO mice) were generated using a Cre-LoxP strategy. beta/H1beta-KO mice had normal growth, fertility, fed or fasted plasma glucose and insulin levels, pancreatic insulin content, and insulin sensitivity. However, beta/H1beta-KO mice exhibited impaired glucose tolerance with reduced insulin secretion compared with wild-type mice but preserved a normal insulin secretory response to arginine. Moreover, beta/H1beta-KO islets had increased HNF1alpha and Pdx-1, decreased HNF4 mRNA levels, and reduced glucose-stimulated insulin release. These results indicate that HNF1beta is involved in regulating the beta-cell transcription factor network and is necessary for glucose sensing or glycolytic signaling.

Expression of the alpha7 isoform of hepatocyte nuclear factor (HNF) 4 is activated by HNF6/OC-2 and HNF1 and repressed by HNF4alpha1 in the liver

The hepatocyte nuclear factor (HNF) 4alpha gene possesses two promoters, proximal P1 and distal P2, whose use results in HNF4alpha1 and HNF4alpha7 transcripts, respectively. Both isoforms are expressed in the embryonic liver, whereas HNF4alpha1 is almost exclusively in the adult liver. A 516-bp fragment, encompassing a DNase I-hypersensitive site associated with P2 activity that is still retained in adult liver, contains functional HNF1 and HNF6 binding sites and confers full promoter activity in transient transfections. We demonstrate a critical role of the Onecut factors in P2 regulation using site-directed mutagenesis and embryos doubly deficient for HNF6 and OC-2 that show reduced hepatic HNF4alpha7 transcript levels. Transient transgenesis showed that a 4-kb promoter region is sufficient to drive expression of a reporter gene in the stomach, intestine, and pancreas, but not the liver, for which additional activating sequences may be required. Quantitative PCR analysis revealed that throughout liver development HNF4alpha7 transcripts are lower than those of HNF4alpha1. HNF4alpha1 represses P2 activity in transfection assays and as deduced from an increase in P2-derived transcript levels in recombinant mice in which HNF4alpha1 has been deleted and replaced by HNF4alpha7. We conclude that although HNF6/OC-2 and perhaps HNF1 activate the P2 promoter in the embryo, increasing HNF4alpha1 expression throughout development causes a switch to essentially exclusive P1 promoter activity in the adult liver.

Bipotential mouse embryonic liver stem cell lines contribute to liver regeneration and differentiate as bile ducts and hepatocytes

Cell lines have many advantages: they can be manipulated genetically, expanded, and stockpiled for organ transplantation. Freshly isolated hepatocytes, oval cells, pancreatic cells, and hematopoietic stem cells have been shown to repopulate the damaged liver. Here we show that bipotential mouse embryonic liver (BMEL) stem cell lines participate in liver regeneration in albumin-urokinase plasminogen activator/severe combined immunodeficiency disease (Alb-uPA/SCID) transgenic mice. In the liver, BMEL-GFP cells proliferate and differentiate into both hepatocytes and bile ducts, forming small to large clusters detected throughout the 3-8 weeks analyzed after transplantation. Moreover, they respond like host cells to signals for growth, differentiation, and even zonal expression of metabolic enzymes, showing regulated expression of cytokeratins and liver-enriched transcription factors. Immunostaining for MHC class I molecules revealed that cells do not coexpress donor and recipient H-2 haplotypes, as would be the case had cell fusion occurred. This report shows that immortalized stem cell lines not only are competent to participate in the repair of a damaged tissue but also can differentiate into the two major epithelial cell types of a complex organ, hepatocytes and bile ducts.

Functions of HNF1 family members in differentiation of the visceral endoderm cell lineage

The two members of the hepatocyte nuclear factor 1 (HNF1) transcription factor family, HNF1 and variant HNF1 (vHNF1), show a strong homology in their atypical POU-homeodomain and dimerization domain but differ in their transactivation domains. Moreover, two vHNF1 isoforms generated by alternative splicing are present in all tissues expressing this gene. vHnf1-deficient mouse embryos die soon after implantation due to defective visceral endoderm formation, an extraembryonic tissue essential for development and survival of the embryo proper. In contrast, invalidation of Hnf1, which is expressed at later developmental stages than vHnf1, does not lead to embryonic lethality or developmental defects. To examine the specific or potential equivalent functions of vHNF1 isoforms and HNF1 during the process of visceral endoderm differentiation, we stably reexpressed these factors in vHnf1-deficient embryonic stem cells. Analysis of these embryonic stem cells upon differentiation into embryoid bodies shows that vHNF1 isoforms exhibit specific behaviors depending on particular target genes and cooperate in the establishment of a functional visceral endoderm. Furthermore, forced expression of HNF1 in vHnf1-deficient embryonic stem cells fully restores the formation of a mature visceral endoderm with the correct expression profile of early and late markers of this lineage. Thus, in this context, HNF1 functionally replaces both vHNF1 isoforms, suggesting that the different developmental functions of these transcription factors are mainly due to the acquisition of novel expression patterns.

Mouse Mix gene is activated early during differentiation of ES and F9 stem cells and induces endoderm in frog embryos

In frog and zebrafish, the Mix/Bix family of paired type homeodomain proteins play key roles in specification and differentiation of mesendoderm. However, in mouse, only a single Mix gene (mMix) has been identified to date and its function is unknown. We have analyzed the expression of mouse Mix RNA and protein in embryos, embryoid bodies formed from embryonic stem cells and F9 teratocarcinoma cells, as well as several differentiated cell types. Expression in embryoid bodies in culture mirrors that in embryos, where Mix is transcribed transiently in primitive (visceral) endoderm (VE) and in nascent mesoderm. In F9 cells induced by retinoic acid to differentiate to VE, mMix is coordinately expressed with three other endodermal transcription factors, well before AFP, and its protein product is localized to the nucleus. In a subpopulation of nascent mesodermal cells from embryonic stem cell embryoid bodies, mMix is coexpressed with Brachyury. Intriguingly, mMix mRNA is detected in a population (T+Flk1+) of cells which may contain hemangioblasts, before the onset of hematopoiesis and activation of hematopoietic markers. In vitro and in vivo, mMix expression in nascent mesoderm is rapidly down-regulated and becomes undetectable in differentiated cell types. In the region of the developing gut, mMix expression is confined to the mesoderm of mid- and hindgut but is absent from definitive endoderm. Injection of mouse mMix RNA into early frog embryos results in axial truncation of developing tadpoles and, in animal cap assays, mMix alone is sufficient to activate expression of several endodermal (but not mesodermal) markers. Although these observations do not exclude a possible cell-autonomous function for mMix in mesendodermal progenitor cells, they do suggest an additional, non-cell autonomous role in nascent mesoderm in the formation and/or patterning of adjacent definitive endoderm.

Embryonic liver cells and permanent lines as models for hepatocyte and bile duct cell differentiation

Analysis of liver cells during development is facilitated by the possibility of complementing in vivo analysis with experiments on cultured cells. In this review, we discuss results from several laboratories concerning bipotential hepatic stem cells from mouse (HBC-3, H-CFU-C, MMH and BMEL), rat (rhe14321) and primate (IPFLS) embryos. Several groups have used fluorescence-activated cell sorting to identify clonogenic bipotential cells; others have derived bipotential cell lines by plating liver cell suspensions and cloning. The bipotential cells, which probably originate from hepatoblasts, can differentiate as hepatocytes or bile duct cells, and undergo morphogenesis in culture. Disparities in differentiation can be explained by distinct medium compositions, extracellular matrix coated culture surfaces, and gene expression detection methods. Potential applications of these cell lines are discussed.

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.

Hepatocyte nuclear factor 1 alpha controls renal expression of the Npt1-Npt4 anionic transporter locus

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a transcription factor that is expressed in liver, pancreas, kidney and intestine. Mice lacking HNF1alpha are born normally but suffer from several defects including hyperphenylalaninemia, defective bile acid and cholesterol metabolism, an insulin secretion defect and renal Fanconi syndrome. The renal phenotype involves a defect in renal proximal tubule reabsorption, leading to polyuria, glucosuria, aminoaciduria and phosphaturia. We investigated the expression of genes encoding members of the sodium/phosphate cotransporter (Na(+)/Pi) family (namely Npt1, Npt2, Npt4 and Ram1). We show that Npt1 and Npt4 genes were expressed at reduced levels in the kidneys of HNF1alpha -/- mice, whereas the expression of Npt2, the major renal phosphate transporter, was not affected. Analysis of the Npt1 genomic sequence revealed the existence of several alternative promoters activated in liver and/or in kidney. All of these were down-regulated in the kidneys of HNF1alpha -/- animals. Several HNF1alpha binding sites (BS) play an important role in the transcriptional control of this locus, including low-affinity HNF1 BSs localised in a DNase I hypersensitivity site (HSS3). Transient transfection experiments confirmed that HNF1alpha directly transactivates the Npt1 promoter and that the HSS3 region contributes to this activation.

Regulation of kidney-specific Ksp-cadherin gene promoter by hepatocyte nuclear factor-1beta

Kidney-specific cadherin (Ksp-cadherin) is a tissue-specific member of the cadherin family that is expressed exclusively in the kidney and developing genitourinary tract. Recent studies have shown that the proximal 250 bp of the Ksp-cadherin gene promoter are sufficient to direct tissue-specific gene expression in vivo and in vitro. The proximal 120 bp of the promoter are evolutionarily conserved between mouse and human and contain a DNase I hypersensitive site that is kidney cell specific. At position -55, the promoter contains a consensus recognition site for hepatocyte nuclear factor-1 (HNF-1). Mutations of the consensus HNF-1 site and downstream GC-boxes inhibit promoter activity in transfected cells. HNF-1alpha and HNF-1beta bind specifically to the -55 site, and both proteins transactivate the promoter directly. Expression of Ksp-cadherin is not altered in the kidneys of HNF-1alpha-deficient mice. However, expression of a gain-of-function HNF-1beta mutant stimulates Ksp-cadherin promoter activity in transfected cells, whereas expression of a dominant-negative mutant inhibits activity. These studies identify Ksp-cadherin as the first kidney-specific promoter that has been shown to be regulated by HNF-1beta. Mutations of HNF-1beta, as occur in humans with inherited renal cysts and diabetes, may cause dysregulated Ksp-cadherin promoter activity.