Evelyne Fischer

Defective planar cell polarity in polycystic kidney disease

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.

A transcriptional network in polycystic kidney disease

Mutations in cystic kidney disease genes represent a major genetic cause of end‐stage renal disease. However, the molecular cascades controlling the expression of these genes are still poorly understood. Hepatocyte Nuclear Factor 1β (HNF1β) is a homeoprotein predominantly expressed in renal, pancreatic and hepatic epithelia. We report here that mice with renal‐specific inactivation of HNF1β develop polycystic kidney disease. We show that renal cyst formation is accompanied by a drastic defect in the transcriptional activation of Umod, Pkhd1 and Pkd2 genes, whose mutations are responsible for distinct cystic kidney syndromes. In vivo chromatin immunoprecipitation experiments demonstrated that HNF1β binds to several DNA elements in murine Umod, Pkhd1, Pkd2 and Tg737/Polaris genomic sequences. Our results uncover a direct transcriptional hierarchy between HNF1β and cystic disease genes. Interestingly, most of the identified HNF1β target gene products colocalize to the primary cilium, a crucial organelle that plays an important role in controlling the proliferation of tubular cells. This may explain the increased proliferation of cystic cells in MODY5 patients carrying autosomal dominant mutations in HNF1β.

Parathyroid hormone‐related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so‐called ‘parathyroid hormone‐related protein’ (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N‐terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly‐hormone which comprises a family of distinct peptide hormones arising from post‐translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N‐terminal, mid‐region and C‐terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1‐34) and PTHrP(1‐36), is the only cloned receptor so far. PTHrP is a PTH‐like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo‐vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium‐sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

A mitotic transcriptional switch in polycystic kidney disease

Hepatocyte nuclear factor-1β (HNF-1β) 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-1β. 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-1β might be involved in reprogramming gene expression after transcriptional silencing is induced by mitotic chromatin condensation. Notably, HNF-1β remains associated with the mitotically condensed chromosomal barrels. This association suggests that HNF-1β is a bookmarking factor that is necessary for reopening the chromatin of target genes after mitotic silencing.

Progress in the thermodynamic modelling of the O–U binary system

Abstract The fuel of civil nuclear plants, UO 2 , melts at 3120 K. During an hypothetical severe accident, urania, submitted to high temperatures and various oxygen potentials, presents a wide non-stoichiometry range: the melting temperature of UO 2± x , related to oxygen potential, decreases in all cases. In this scenario, urania could react with other materials, firstly zircaloy, and the melting temperature of (U, Zr)O 2± x still decreases. That is why the critical assessment of the O–U binary system including the non-stoichiometry range of urania, is a major step to a correct thermodynamic modelling of multicomponent systems for nuclear safety. The very numerous experimental information has been compiled and analysed. The associate model was used for the liquid phase, and a sublattice model for UO 2± x ; U 4 O 9− y , U 3 O 8 and UO 3 were treated as stoichiometric. Phase diagram and thermodynamic properties have been calculated from the optimised Gibbs energy parameters. The calculated consistency with the experimental ones is quite satisfactory.

Mutations of HNF-1β inhibit epithelial morphogenesis through dysregulation of SOCS-3

Hepatocyte nuclear factor-1β (HNF-1β) is a Pit-1, Oct-1/2, Unc-86 (POU) homeodomain-containing transcription factor expressed in the kidney, liver, pancreas, and other epithelial organs. Mutations of HNF-1β cause maturity-onset diabetes of the young, type 5 (MODY5), which is characterized by early-onset diabetes mellitus and congenital malformations of the kidney, pancreas, and genital tract. Knockout of HNF-1β in the mouse kidney results in cyst formation. However, the signaling pathways and transcriptional programs controlled by HNF-1β are poorly understood. Using genome-wide chromatin immunoprecipitation and DNA microarray (ChIP-chip) and microarray analysis of mRNA expression, we identified SOCS3 (suppressor of cytokine signaling-3) as a previously unrecognized target gene of HNF-1β in the kidney. HNF-1β binds to the SOCS3 promoter and represses SOCS3 transcription. The expression of SOCS3 is increased in HNF-1β knockout mice and in renal epithelial cells expressing dominant-negative mutant HNF-1β. Increased levels of SOCS-3 inhibit HGF-induced tubulogenesis by decreasing phosphorylation of Erk and STAT-3. Conversely, knockdown of SOCS-3 in renal epithelial cells expressing dominant-negative mutant HNF-1β rescues the defect in HGF-induced tubulogenesis by restoring phosphorylation of Erk and STAT-3. Thus, HNF-1β regulates tubulogenesis by controlling the levels of SOCS-3 expression. Manipulating the levels of SOCS-3 may be a useful therapeutic approach for human diseases induced by HNF-1β mutations.

Thermodynamic modelling of the O-U-Zr system

To increase the basic knowledge of key phenomena which occur during the molten corium–concrete interaction (MCCI) resulting from the event of a severe accident in a nuclear power plant, we are developing a thermodynamic database for the corium (TDBCR) including the main materials involved. The first step of the accident is the core degradation, resulting from the interaction of the fuel (UO2) with the zircaloy (98 wt% Zr). That is why the thermodynamic modelling of the fundamental O–U–Zr system is performed from a critical assessment of all the available experimental information. Optimized Gibbs energy parameters are given, and comparison between calculated and experimental equilibrium phase diagrams or thermodynamic properties is presented both for binary sub-systems and the ternary one, by means of isothermal (up to 3300 K) and isopleth sections of particular interest. The extent of the O–U liquid miscibility gap into the ternary system is especially discussed.

HNF-1β 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.

A thermodynamic evaluation of the Mn-Si system

Abstract Available experimental information concerning thermodynamic properties as well as phase equilibria has been compiled and used for the assessment of new self-consistent parameters for all phases in the Mn-Si system, by means of the well-known Lukas et al. s program. Phase diagram and characteristic thermodynamic functions have been calculated and compared with the experimental values, leading to a very satisfactory agreement. Thermodynamic models and pure elements data are consistent with the S.G.T.E (Scientific Groupe Thermodata Europe) recommendations. Thus, the assessed parameters may be incorporated in specialized solution databases.

Thermodynamic modelling of the N–U system

Abstract Thermodynamic properties constitute part of our general knowledge about physical and chemical properties of nuclear materials, as the solid substance UN 1− x (fcc_B1). This is why the thermodynamic modelling of the N–U binary system is performed here from a critical assessment of most of the available experimental information, with one of the most commonly used optimization procedure. Optimized Gibbs energy parameters are given, and a comparison between the calculated and experimental equilibrium phase diagram or thermodynamic properties is presented.