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Hepatocyte nuclear factor-1beta (HNF-1beta) is a transcription factor required for the expression of several renal cystic genes and whose prenatal deletion leads to polycystic kidney disease (PKD). We show here that inactivation of Hnf1b from postnatal day 10 onward does not elicit cystic dilations in tubules after their proliferative morphogenetic elongation is over. Cystogenic resistance is intrinsically linked to the quiescent state of cells. In fact, when Hnf1b deficient quiescent cells are forced to proliferate by an ischemia-reperfusion injury, they give rise to cysts, owing to loss of oriented cell division. Remarkably, in quiescent cells, the transcription of crucial cystogenic target genes is maintained even in the absence of HNF-1beta. However, their expression is lost as soon as cells proliferate and the chromatin of target genes acquires heterochromatin marks. These results unveil a previously undescribed aspect of gene regulation. It is well established that transcription is shut off during the mitotic condensation of chromatin. We propose that transcription factors such as HNF-1beta might be involved in reprogramming gene expression after transcriptional silencing is induced by mitotic chromatin condensation. Notably, HNF-1beta remains associated with the mitotically condensed chromosomal barrels. This association suggests that HNF-1beta is a bookmarking factor that is necessary for reopening the chromatin of target genes after mitotic silencing.

Hepatocyte nuclear factor 1 α ( HNF1 α) is a transcription factor that is expressed in liver, pancreas, kidney and intestine. Mice lacking HNF1 α 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 HNF1 α −/− 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 HNF1 α −/− animals. Several HNF1 α 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 HNF1 α directly transactivates the Npt1 promoter and that the HSS3 region contributes to this activation.

The terminal components of the complement system contribute to host defense by forming the multiprotein membrane attack complex (MAC) which is responsible for cell lysis and several noncytotoxic effects. Most of the complement proteins are synthesized in the liver, but the mechanisms controlling their tissue-specific expression have not been elucidated. In this study we show that mice lacking the hepatic transcription factor hepatocyte nuclear factor 1alpha (HNF1alpha) fail to transcribe C5 and C8A complement genes. In addition, mRNAs encoding for several other terminal complement components or subunits are expressed at lower levels, including C8beta, C8gamma, and C9. We next used a reconstitution assay involving human sera with selective complement deficiencies to assess mouse complement activity. Sera from HNF1alpha-deficient mice showed negligible hemolytic activity of both C5 and C8alpha-gamma subunits. The activity of C8beta was severely affected despite only a 50% reduction in C8beta mRNA levels in the liver. This is reminiscent of C8alpha-gamma-deficient patients who accumulate extremely low levels of the C8beta subunit. Our results demonstrate that HNF1alpha plays a key role in the expression of C5 and C8A genes, two terminal complement component genes that are essential for the assembly of MAC as a result of complement activation.

Recently it has been shown that dominant mutations in the human hepatocyte nuclear factor 1alpha (HNF1alpha) gene, encoding for a homeoprotein that is expressed in liver, kidney, pancreas and intestine, result in maturity onset diabetes of the young type 3 (MODY3). HNF1alpha-null mice are diabetic, but at the same time suffer from a renal Fanconi syndrome characterized by urinary glucose loss. Here we show that MODY3 patients are also characterized by a reduced tubular reabsorption of glucose. The renal murine defect is due to reduced expression of the low affinity/high capacity glucose cotransporter (SGLT2). Our results show that HNF1alpha directly controls SGLT2 gene expression. Together these data indicate that HNF1alpha plays a key role in glucose homeostasis in mammals.

Mutations in the gene for the transcription factor hepatocyte nuclear factor (HNF) 1alpha cause maturity-onset diabetes of the young (MODY) 3, a form of diabetes that results from defects in insulin secretion. Since the nature of these defects has not been defined, we compared insulin secretory function in heterozygous [HNF-1alpha (+/-)] or homozygous [HNF-1alpha (-/-)] mice with null mutations in the HNF-1alpha gene with their wild-type littermates [HNF-1alpha (+/+)]. Blood glucose concentrations were similar in HNF-1alpha (+/+) and (+/-) mice (7.8+/-0.2 and 7.9+/-0.3 mM), but were significantly higher in the HNF-1alpha (-/-) mice (13.1+/-0.7 mM, P < 0.001). Insulin secretory responses to glucose and arginine in the perfused pancreas and perifused islets from HNF-1alpha (-/-) mice were < 15% of the values in the other two groups and were associated with similar reductions in intracellular Ca2+ responses. These defects were not due to a decrease in glucokinase or insulin gene transcription. beta cell mass adjusted for body weight was not reduced in the (-/-) animals, although pancreatic insulin content adjusted for pancreas weight was slightly lower (0.06+/-0.01 vs. 0.10+/-0.01 microg/mg, P < 0.01) than in the (+/+) animals. In summary, a null mutation in the HNF-1alpha gene in homozygous mice leads to diabetes due to alterations in the pathways that regulate beta cell responses to secretagogues including glucose and arginine. These results provide further evidence in support of a key role for HNF-1alpha in the maintenance of normal beta cell function.

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a homeoprotein that is expressed in the liver, kidney, pancreas, and digestive tract. Its inactivation in mouse resulted in decreased transcription of known target genes such as albumin and alpha1-antitrypsin. In contrast, the phenylalanine hydroxylase (PAH) gene was totally silent and unresponsive to normal inducers like glucocorticoids and cyclic AMP in the liver. DNase I and micrococcal nuclease digestion of liver nuclei showed that HNF1alpha inactivation had drastic effects on the chromatin structure of the PAH regulatory regions. Three DNase I-hypersensitive sites (HSSI, HSSII, and HSSIII), typical of the actively transcribed PAH gene, were undetectable in liver from HNF1alpha-deficient animals. Both HSSII and HSSIII elements harbor HNF1 sites, but only the latter has detectable enhancer activity in transient-transfection assays. In addition, the PAH promoter in livers of HNF1alpha-deficient animals was methylated. These results suggest that HNF1alpha could activate transcription through two mechanisms. One implies participation in the recruitment of the general transcription machinery to the promoter, and the second involves the remodeling of chromatin structure and demethylation that would allow transcription factors to interact with their cognate cis-acting elements.

International audience; Morphogenesis involves coordinated proliferation, differentiation and spatial distribution of cells. We show that lengthening of renal tubules is associated with mitotic orientation of cells along the tubule axis, demonstrating intrinsic planar cell polarization, and we demonstrate that mitotic orientations are significantly distorted in rodent polycystic kidney models. These results suggest that oriented cell division dictates the maintenance of constant tubule diameter during tubular lengthening and that defects in this process trigger renal tubular enlargement and cyst formation.

International audience; OBJECTIVES: Candida albicans is the most prevalent fungal pathogen of humans, causing a wide range of infections from harmless superficial to severe systemic infections. Improvement of the antifungal arsenal is needed since existing antifungals can be associated with limited efficacy, toxicity and antifungal resistance. Here we aimed to identify compounds that act synergistically with echinocandin antifungals and that could contribute to a faster reduction of the fungal burden. METHODS: A total of 38 758 compounds were tested for their ability to act synergistically with aminocandin, a β-1,3-glucan synthase inhibitor of the echinocandin family of antifungals. The synergy between echinocandins and an identified hit was studied with chemogenomic screens and testing of individual Saccharomyces cerevisiae and C. albicans mutant strains. RESULTS: We found that colistin, an antibiotic that targets membranes in Gram-negative bacteria, is synergistic with drugs of the echinocandin family against all Candida species tested. The combination of colistin and aminocandin led to faster and increased permeabilization of C. albicans cells than either colistin or aminocandin alone. Echinocandin susceptibility was a prerequisite to be able to observe the synergy. A large-scale screen for genes involved in natural resistance of yeast cells to low doses of the drugs, alone or in combination, identified efficient sphingolipid and chitin biosynthesis as necessary to protect S. cerevisiae and C. albicans cells against the antifungal combination. CONCLUSIONS: These results suggest that echinocandin-mediated weakening of the cell wall facilitates colistin targeting of fungal membranes, which in turn reinforces the antifungal activity of echinocandins.

HNF1 is a transcriptional activator of many hepatic genes including albumin, alpha1-antitrypsin, and alpha- and beta-fibrinogen. It is related to the homeobox gene family and is predominantly expressed in liver and kidney. Mice lacking HNF1 fail to thrive and die around weaning after a progressive wasting syndrome with a marked liver enlargement. The transcription rate of genes like albumin and alpha1-antitrypsin is reduced, while the gene coding for phenylalanine hydroxylase is totally silent, giving rise to phenylketonuria. Mutant mice also suffer from severe Fanconi syndrome caused by renal proximal tubular dysfunction. The resulting massive urinary glucose loss leads to energy and water wasting. HNF1-deficient mice may provide a model for human renal Fanconi syndrome.

The intestinal epithelium is a complex system characterized by massive and continuous cell renewal and differentiation. In this context, cell-type-specific transcription factors are thought to play a crucial role by modulating specific transcription networks and signalling pathways. Hnf1alpha and beta are closely related atypical homeoprotein transcription factors expressed in several epithelia, including the gut. With the use of a conditional inactivation system, we generated mice in which Hnf1b is specifically inactivated in the intestinal epithelium on a wild-type or Hnf1a(-/-) genetic background. Whereas the inactivation of Hnf1a or Hnf1b alone did not lead to any major intestinal dysfunction, the concomitant inactivation of both genes resulted in a lethal phenotype. Double-mutant animals had defective differentiation and cell fate commitment. The expression levels of markers of all the differentiated cell types, both enterocytes and secretory cells, were affected. In addition, the number of goblet cells was increased, whereas mature Paneth cells were missing. At the molecular level, we show that Hnf1alpha and beta act upstream of the Notch pathway controlling directly the expression of two crucial components: Jag1 and Atoh1. We demonstrate that the double-mutant mice present with a defect in intestinal water absorption and that Hnf1alpha and beta directly control the expression of Slc26a3, a gene whose mutations are associated with chloride diarrhoea in human patients. Our study identifies new direct target genes of the Hnf1 transcription factors and shows that they play crucial roles in both defining cell fate and controlling terminal functions in the gut epithelium.