Ingo Kurth

Publications (17)172.08 Total impact

• Article: Renal intercalated cells are rather energized by a proton than a sodium pump.

  Régine Chambrey, Ingo Kurth, Janos Peti-Peterdi, Pascal Houillier, Jeffrey M Purkerson, Françoise Leviel, Moritz Hentschke, Anselm A Zdebik, George J Schwartz, Christian A Hübner, Dominique Eladari
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  ABSTRACT: The Na(+) concentration of the intracellular milieu is very low compared with the extracellular medium. Transport of Na(+) along this gradient is used to fuel secondary transport of many solutes, and thus plays a major role for most cell functions including the control of cell volume and resting membrane potential. Because of a continuous leak, Na(+) has to be permanently removed from the intracellular milieu, a process that is thought to be exclusively mediated by the Na(+)/K(+)-ATPase in animal cells. Here, we show that intercalated cells of the mouse kidney are an exception to this general rule. By an approach combining two-photon imaging of isolated renal tubules, physiological studies, and genetically engineered animals, we demonstrate that inhibition of the H(+) vacuolar-type ATPase (V-ATPase) caused drastic cell swelling and depolarization, and also inhibited the NaCl absorption pathway that we recently discovered in intercalated cells. In contrast, pharmacological blockade of the Na(+)/K(+)-ATPase had no effects. Basolateral NaCl exit from β-intercalated cells was independent of the Na(+)/K(+)-ATPase but critically relied on the presence of the basolateral ion transporter anion exchanger 4. We conclude that not all animal cells critically rely on the sodium pump as the unique bioenergizer, but can be replaced by the H(+) V-ATPase in renal intercalated cells. This concept is likely to apply to other animal cell types characterized by plasma membrane expression of the H(+) V-ATPase.
  Proceedings of the National Academy of Sciences 04/2013; · 9.68 Impact Factor
• Article: Exome sequencing identifies a REEP1 mutation involved in distal hereditary motor neuropathy type V.

  Christian Beetz, Thomas R Pieber, Nicole Hertel, Maria Schabhüttl, Carina Fischer, Slave Trajanoski, Elisabeth Graf, Silke Keiner, Ingo Kurth, Thomas Wieland, Rita-Eva Varga, Vincent Timmerman, Mary M Reilly, Tim M Strom, Michaela Auer-Grumbach
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  ABSTRACT: The distal hereditary motor neuropathies (dHMNs) are a heterogeneous group of neurodegenerative disorders affecting the lower motoneuron. In a family with both autosomal-dominant dHMN and dHMN type V (dHMN/dHMN-V) present in three generations, we excluded mutations in all genes known to be associated with a dHMN phenotype through Sanger sequencing and defined three potential loci through linkage analysis. Whole-exome sequencing of two affected individuals revealed a single candidate variant within the linking regions, i.e., a splice-site alteration in REEP1 (c.304-2A>G). A minigene assay confirmed complete loss of splice-acceptor functionality and skipping of the in-frame exon 5. The resulting mRNA is predicted to be expressed at normal levels and to encode an internally shortened protein (p.102_139del). Loss-of-function REEP1 mutations have previously been identified in dominant hereditary spastic paraplegia (HSP), a disease associated with upper-motoneuron pathology. Consistent with our clinical-genetic data, we show that REEP1 is strongly expressed in the lower motoneurons as well. Upon exogeneous overexpression in cell lines we observe a subcellular localization defect for p.102_139del that differs from that observed for the known HSP-associated missense mutation c.59C>A (p.Ala20Glu). Moreover, we show that p.102_139del, but not p.Ala20Glu, recruits atlastin-1, i.e., one of the REEP1 binding partners, to the altered sites of localization. These data corroborate the loss-of-function nature of REEP1 mutations in HSP and suggest that a different mechanism applies in REEP1-associated dHMN.
  The American Journal of Human Genetics 06/2012; 91(1):139-45. · 10.60 Impact Factor
• Article: Deletions in PITX1 cause a spectrum of lower-limb malformations including mirror-image polydactyly.

  Eva Klopocki, Christian Kähler, Nicola Foulds, Hitesh Shah, Benjamin Joseph, Hermann Vogel, Sabine Lüttgen, Rainer Bald, Regina Besoke, Karsten Held, Stefan Mundlos, Ingo Kurth
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  ABSTRACT: PITX1 is a bicoid-related homeodomain transcription factor implicated in vertebrate hindlimb development. Recently, mutations in PITX1 have been associated with autosomal-dominant clubfoot. In addition, one affected individual showed a polydactyly and right-sided tibial hemimelia. We now report on PITX1 deletions in two fetuses with a high-degree polydactyly, that is, mirror-image polydactyly. Analysis of DNA from additional individuals with isolated lower-limb malformations and higher-degree polydactyly identified a third individual with long-bone deficiency and preaxial polydactyly harboring a heterozygous 35 bp deletion in PITX1. The findings demonstrate that mutations in PITX1 can cause a broad spectrum of isolated lower-limb malformations including clubfoot, deficiency of long bones, and mirror-image polydactyly.
  European journal of human genetics: EJHG 01/2012; 20(6):705-8. · 3.56 Impact Factor
• Article: Duplications of BHLHA9 are associated with ectrodactyly and tibia hemimelia inherited in non-Mendelian fashion.

  Eva Klopocki, Silke Lohan, Sandra C Doelken, Sigmar Stricker, Charlotte W Ockeloen, Renata Soares Thiele de Aguiar, Karina Lezirovitz, Regina Celia Mingroni Netto, Aleksander Jamsheer, Hitesh Shah, [......], Koenraad Devriendt, Ulrike Kordass, Maja Hempel, Anna Rajab, Outi Mäkitie, Mohammed Naveed, Uppala Radhakrishna, Stylianos E Antonarakis, Denise Horn, Stefan Mundlos
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  ABSTRACT: Split-hand/foot malformation (SHFM)-also known as ectrodactyly-is a congenital disorder characterised by severe malformations of the distal limbs affecting the central rays of hands and/or feet. A distinct entity termed SHFLD presents with SHFM and long bone deficiency. Mouse models suggest that a defect of the central apical ectodermal ridge leads to the phenotype. Although six different loci/mutations (SHFM1-6) have been associated with SHFM, the underlying cause in a large number of cases is still unresolved. High resolution array comparative genomic hybridisation (CGH) was performed in patients with SHFLD to detect copy number changes. Candidate genes were further evaluated for expression and function during limb development by whole mount in situ hybridisation and morpholino knock-down experiments. Array CGH showed microduplications on chromosome 17p13.3, a locus previously associated with SHFLD. Detailed analysis of 17 families revealed that this copy number variation serves as a susceptibility factor for a highly variable phenotype with reduced penetrance, particularly in females. Compared to other known causes for SHFLD 17p duplications appear to be the most frequent cause of SHFLD. A ~11.8 kb minimal critical region was identified encompassing a single gene, BHLHA9, a putative basic loop helix transcription factor. Whole mount in situ hybridisation showed expression restricted to the limb bud mesenchyme underlying the apical ectodermal ridge in mouse and zebrafish embryos. Knock down of bhlha9 in zebrafish resulted in shortening of the pectoral fins. Genomic duplications encompassing BHLHA9 are associated with SHFLD and non-Mendelian inheritance characterised by a high degree of non-penetrance with sex bias. Knock-down of bhlha9 in zebrafish causes severe reduction defects of the pectoral fin, indicating a role for this gene in limb development.
  Journal of Medical Genetics 12/2011; 49(2):119-25. · 6.36 Impact Factor
• Article: Nonsense mutations in SMPX, encoding a protein responsive to physical force, result in X-chromosomal hearing loss.

  Antje K Huebner, Marta Gandia, Peter Frommolt, Anika Maak, Eva M Wicklein, Holger Thiele, Janine Altmüller, Florian Wagner, Antonio Viñuela, Luis A Aguirre, Felipe Moreno, Hannes Maier, Isabella Rau, Sebastian Giesselmann, Gudrun Nürnberg, Andreas Gal, Peter Nürnberg, Christian A Hübner, Ignacio del Castillo, Ingo Kurth
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  ABSTRACT: The fact that hereditary hearing loss is the most common sensory disorder in humans is reflected by, among other things, an extraordinary allelic and nonallelic genetic heterogeneity. X-chromosomal hearing impairment represents only a minor fraction of all cases. In a study of a Spanish family the locus for one of the X-chromosomal forms was assigned to Xp22 (DFNX4). We mapped the disease locus in the same chromosomal region in a large German pedigree with X-chromosomal nonsyndromic hearing impairment by using genome-wide linkage analysis. Males presented with postlingual hearing loss and onset at ages 3-7, whereas onset in female carriers was in the second to third decades. Targeted DNA capture with high-throughput sequencing detected a nonsense mutation in the small muscle protein, X-linked (SMPX) of affected individuals. We identified another nonsense mutation in SMPX in patients from the Spanish family who were previously analyzed to map DFNX4. SMPX encodes an 88 amino acid, cytoskeleton-associated protein that is responsive to mechanical stress. The presence of Smpx in hair cells and supporting cells of the murine cochlea indicates its role in the inner ear. The nonsense mutations detected in the two families suggest a loss-of-function mechanism underlying this form of hearing impairment. Results obtained after heterologous overexpression of SMPX proteins were compatible with this assumption. Because responsivity to physical force is a characteristic feature of the protein, we propose that long-term maintenance of mechanically stressed inner-ear cells critically depends on SMPX function.
  The American Journal of Human Genetics 05/2011; 88(5):621-7. · 10.60 Impact Factor
• Source

  Available from: Lance Miller

  Article: The Na+-dependent chloride-bicarbonate exchanger SLC4A8 mediates an electroneutral Na+ reabsorption process in the renal cortical collecting ducts of mice.

  Françoise Leviel, Christian A Hübner, Pascal Houillier, Luciana Morla, Soumaya El Moghrabi, Gaëlle Brideau, Hatim Hassan, Hassan Hatim, Mark D Parker, Ingo Kurth, [......], Vladimir Pech, Kent A Riemondy, R Lance Miller, Edith Hummler, Gary E Shull, Peter S Aronson, Alain Doucet, Susan M Wall, Régine Chambrey, Dominique Eladari
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  ABSTRACT: Regulation of sodium balance is a critical factor in the maintenance of euvolemia, and dysregulation of renal sodium excretion results in disorders of altered intravascular volume, such as hypertension. The amiloride-sensitive epithelial sodium channel (ENaC) is thought to be the only mechanism for sodium transport in the cortical collecting duct (CCD) of the kidney. However, it has been found that much of the sodium absorption in the CCD is actually amiloride insensitive and sensitive to thiazide diuretics, which also block the Na-Cl cotransporter (NCC) located in the distal convoluted tubule. In this study, we have demonstrated the presence of electroneutral, amiloride-resistant, thiazide-sensitive, transepithelial NaCl absorption in mouse CCDs, which persists even with genetic disruption of ENaC. Furthermore, hydrochlorothiazide (HCTZ) increased excretion of Na+ and Cl- in mice devoid of the thiazide target NCC, suggesting that an additional mechanism might account for this effect. Studies on isolated CCDs suggested that the parallel action of the Na+-driven Cl-/HCO3- exchanger (NDCBE/SLC4A8) and the Na+-independent Cl-/HCO3- exchanger (pendrin/SLC26A4) accounted for the electroneutral thiazide-sensitive sodium transport. Furthermore, genetic ablation of SLC4A8 abolished thiazide-sensitive NaCl transport in the CCD. These studies establish what we believe to be a novel role for NDCBE in mediating substantial Na+ reabsorption in the CCD and suggest a role for this transporter in the regulation of fluid homeostasis in mice.
  The Journal of clinical investigation 04/2010; 120(5):1627-35. · 15.39 Impact Factor
• Article: Mutations in FAM134B, encoding a newly identified Golgi protein, cause severe sensory and autonomic neuropathy.

  Ingo Kurth, Torsten Pamminger, J Christopher Hennings, Désirée Soehendra, Antje K Huebner, Annelies Rotthier, Jonathan Baets, Jan Senderek, Haluk Topaloglu, Sandra A Farrell, Gudrun Nürnberg, Peter Nürnberg, Peter De Jonghe, Andreas Gal, Christoph Kaether, Vincent Timmerman, Christian A Hübner
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  ABSTRACT: Hereditary sensory and autonomic neuropathy type II (HSAN II) leads to severe mutilations because of impaired nociception and autonomic dysfunction. Here we show that loss-of-function mutations in FAM134B, encoding a newly identified cis-Golgi protein, cause HSAN II. Fam134b knockdown results in structural alterations of the cis-Golgi compartment and induces apoptosis in some primary dorsal root ganglion neurons. This implicates FAM134B as critical in long-term survival of nociceptive and autonomic ganglion neurons.
  Nature Genetics 11/2009; 41(11):1179-81. · 35.53 Impact Factor
• Article: Duplications of noncoding elements 5' of SOX9 are associated with brachydactyly-anonychia.

  Ingo Kurth, Eva Klopocki, Sigmar Stricker, Jolieke van Oosterwijk, Sebastian Vanek, Jens Altmann, Heliosa G Santos, Jeske J T van Harssel, Thomy de Ravel, Andrew O M Wilkie, Andreas Gal, Stefan Mundlos
  Nature Genetics 09/2009; 41(8):862-3. · 35.53 Impact Factor
• Article: The murine AE4 promoter predominantly drives type B intercalated cell specific transcription.

  Moritz Hentschke, Suna Hentschke, Uwe Borgmeyer, Christian Andreas Hübner, Ingo Kurth
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  ABSTRACT: AE4 is an anion exchanger almost exclusively expressed in the collecting ducts of the kidney. This very restricted expression prompted us to analyze its transcription in more detail. 5' RACE yielded alternative transcriptional start sites that are predicted to code for N-terminal protein variants. Comparison of the 5' genomic sequence between species identified a transcriptionally active region with three conserved spans. In transgenic mice beta-galactosidase expression driven by this fragment resembled endogenous AE4 expression and was predominantly restricted to type B intercalated cells. Hence this promoter could prove useful to target type B intercalated cells by genetic approaches.
  Histochemie 07/2009; 132(4):405-12. · 2.59 Impact Factor
• Article: Missense exchanges in the TTBK2 gene mutated in SCA11.

  Ulf Edener, Ingo Kurth, Annechristin Meiner, Frank Hoffmann, Christian A Hübner, Veronica Bernard, Gabriele Gillessen-Kaesbach, Christine Zühlke
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  ABSTRACT: The spinocerebellar ataxias (SCAs) with autosomal dominant inheritance are a clinically and genetically heterogeneous group of neurological disorders with overlapping as well as highly variable phenotypes primarily affecting the cerebellum. To date, 28 different loci have been identified. Nine SCAs are caused by repeat expansions; for 14 only the chromosomal localisation is known. Recently, two frameshift mutations in the tau tubulin kinase 2 gene (TTBK2) were reported to cause SCA11. To evaluate the frequency of mutations in the TTBK2 gene, we performed molecular genetic analyses in 49 unrelated familial cases with ataxia. Sequencing all coding exons revealed, amongst others, two novel missense exchanges at evolutionarily conserved amino acid positions. Although being unique in 98 alleles of ataxia patients, a disease causing effect can be excluded with high probability for both variations. This result demonstrates the challenges in diagnostic testing for SCA11.
  Journal of Neurology 07/2009; 256(11):1856-9. · 3.47 Impact Factor
• Article: Rdh12 activity and effects on retinoid processing in the murine retina.

  Jared D Chrispell, Kecia L Feathers, Maureen A Kane, Chul Y Kim, Matthew Brooks, Ritu Khanna, Ingo Kurth, Christian A Hübner, Andreas Gal, Alan J Mears, Anand Swaroop, Joseph L Napoli, Janet R Sparrow, Debra A Thompson
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  ABSTRACT: RDH12 mutations are responsible for early-onset autosomal recessive retinal dystrophy, which results in profound retinal pathology and severe visual handicap in patients. To investigate the function of RDH12 within the network of retinoid dehydrogenases/reductases (RDHs) present in retina, we studied the retinal phenotype of Rdh12-deficient mice. In vivo rates of all-trans-retinal reduction and 11-cis-retinal formation during recovery from bleaching were similar in Rdh12-deficient and wild-type mice matched for an Rpe65 polymorphism that impacts visual cycle efficiency. However, retinal homogenates from Rdh12-deficient mice exhibited markedly decreased capacity to reduce exogenous retinaldehydes in vitro. Furthermore, in vivo levels of the bisretinoid compound diretinoid-pyridinium-ethanolamine (A2E) were increased in Rdh12-deficient mice of various genetic backgrounds. Conversely, in vivo levels of retinoic acid and total retinol were significantly decreased. Rdh12 transcript levels in wild-type mice homozygous for the Rpe65-Leu(450) polymorphism were greater than in Rpe65-Met(450) mice and increased during postnatal development in wild-type mice and Nrl-deficient mice having an all-cone retina. Rdh12-deficient mice did not exhibit increased retinal degeneration relative to wild-type mice at advanced ages, when bred on the light-sensitive BALB/c background, or when heterozygous for a null allele of superoxide dismutase 2 (Sod2(+/-)). Our findings suggest that a critical function of RDH12 is the reduction of all-trans-retinal that exceeds the reductive capacity of the photoreceptor outer segments.
  Journal of Biological Chemistry 07/2009; 284(32):21468-77. · 4.77 Impact Factor
• Article: Analysis of rare APC variants at the mRNA level: six pathogenic mutations and literature review.

  Astrid Kaufmann, Stefanie Vogt, Siegfried Uhlhaas, Dietlinde Stienen, Ingo Kurth, Horst Hameister, Elisabeth Mangold, Judith Kötting, Elke Kaminsky, Peter Propping, Waltraut Friedl, Stefan Aretz
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  ABSTRACT: In monogenic disorders, the functional evaluation of rare, unclassified variants helps to assess their pathogenic relevance and can improve differential diagnosis and predictive testing. We characterized six rare APC variants in patients with familial adenomatous polyposis at the mRNA level. APC variants c.531 + 5G>C and c.532-8G>A in intron 4, c.1409-2_1409delAGG in intron 10, c.1548G>A in exon 11, and a large duplication of exons 10 and 11 result in a premature stop codon attributable to aberrant transcripts whereas the variant c.1742A>G leads to the in-frame deletion of exon 13 and results in the removal of a functional motif. Mutation c.1548G>A was detected in the index patient but not in his affected father, suggesting mutational mosaicism. A literature review shows that most of the rare APC variants detected by routine diagnostics and further analyzed at the transcript level were evaluated as pathogenic. The majority of rare APC variants, particularly those located close to exon-intron boundaries, could be classified as pathogenic because of aberrant splicing. Our study shows that the characterization of rare variants at the mRNA level is crucial for the evaluation of pathogenicity and underlying mutational mechanisms, and could lead to better treatment modalities.
  Journal of Molecular Diagnostics 02/2009; 11(2):131-9. · 3.58 Impact Factor
• Article: Mice with targeted Slc4a10 gene disruption have small brain ventricles and show reduced neuronal excitability.

  Stefan Jacobs, Eva Ruusuvuori, Sampsa T Sipilä, Aleksi Haapanen, Helle H Damkier, Ingo Kurth, Moritz Hentschke, Michaela Schweizer, York Rudhard, Linda M Laatikainen, Jaana Tyynelä, Jeppe Praetorius, Juha Voipio, Christian A Hübner
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  ABSTRACT: Members of the SLC4 bicarbonate transporter family are involved in solute transport and pH homeostasis. Here we report that disrupting the Slc4a10 gene, which encodes the Na(+)-coupled Cl(-)-HCO(3)(-) exchanger Slc4a10 (NCBE), drastically reduces brain ventricle volume and protects against fatal epileptic seizures in mice. In choroid plexus epithelial cells, Slc4a10 localizes to the basolateral membrane. These cells displayed a diminished recovery from an acid load in KO mice. Slc4a10 also was expressed in neurons. Within the hippocampus, the Slc4a10 protein was abundant in CA3 pyramidal cells. In the CA3 area, propionate-induced intracellular acidification and attenuation of 4-aminopyridine-induced network activity were prolonged in KO mice. Our data indicate that Slc4a10 is involved in the control of neuronal pH and excitability and may contribute to the secretion of cerebrospinal fluid. Hence, Slc4a10 is a promising pharmacological target for the therapy of epilepsy or elevated intracranial pressure.
  Proceedings of the National Academy of Sciences 02/2008; 105(1):311-6. · 9.68 Impact Factor
• Article: Targeted disruption of the murine retinal dehydrogenase gene Rdh12 does not limit visual cycle function.

  Ingo Kurth, Debra A Thompson, Klaus Rüther, Kecia L Feathers, Jared D Chrispell, Jana Schroth, Christina L McHenry, Michaela Schweizer, Sergej Skosyrski, Andreas Gal, Christian A Hübner
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  ABSTRACT: RDH12 codes for a member of the family of short-chain alcohol dehydrogenases/reductases proposed to function in the visual cycle that supplies the chromophore 11-cis retinal to photoreceptor cells. Mutations in RDH12 cause severe and progressive childhood onset autosomal-recessive retinal dystrophy, including Leber congenital amaurosis. We generated Rdh12 knockout mice, which exhibited grossly normal retinal histology at 10 months of age. Levels of all-trans and 11-cis retinoids in dark- and light-adapted animals and scotopic and photopic electroretinogram (ERG) responses were similar to those for the wild type, as was recovery of the ERG response following bleaching, for animals matched for an Rpe65 polymorphism (p.L450M). Lipid peroxidation products and other measures of oxidative stress did not appear to be elevated in Rdh12(-/-) animals. RDH12 was localized to photoreceptor inner segments and the outer nuclear layer in both mouse and human retinas by immunohistochemistry. The present findings, together with those of earlier studies showing only minor functional deficits in mice deficient for Rdh5, Rdh8, or Rdh11, suggest that the activity of any one isoform is not rate limiting in the visual response.
  Molecular and Cellular Biology 03/2007; 27(4):1370-9. · 5.53 Impact Factor
• Article: Germ cell nuclear factor is a repressor of CRIPTO-1 and CRIPTO-3.

  Moritz Hentschke, Ingo Kurth, Uwe Borgmeyer, Christian A Hübner
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  ABSTRACT: The pluripotency of embryonic stem and embryonic carcinoma cells is maintained by the expression of a set of "stemness" genes. Whereas these genes are down-regulated upon induction of differentiation, the germ cell nuclear factor (GCNF) is transiently up-regulated and represses several pluripotency genes. CRIPTO-1, a co-receptor for the morphogen nodal, is strongly expressed in undifferentiated cells and is rapidly down-regulated during retinoic acid-induced differentiation. Although CRIPTO-1 is expressed at very low levels in adult tissues under normal conditions, it is found highly expressed in a broad range of tumors, where it acts as a potent oncogene. We show that expression of CRIPTO-1 is directly repressed by GCNF during differentiation of the human teratocarcinoma cell line, NT2. GCNF bound to a DR0 element of the CRIPTO-1 promoter in vitro, as shown by electrophoretic mobility shift assays, and in vivo, as demonstrated by chromatin immunoprecipitation. Reporter gene assays demonstrated that GCNF-mediated repression of the CRIPTO-1 promoter is dependent upon the DR0 site. Overexpression of GCNF in NT2 cells resulted in repression of CRIPTO-1 transcription, whereas expression of the transcription-activating fusion construct GCNF-VP16 led to an induction of the CRIPTO-1 gene and prevented its retinoic acid-induced down-regulation. Furthermore, we demonstrated that CRIPTO-3, a processed pseudogene of CRIPTO-1 on the X chromosome, is expressed in undifferentiated NT2 cells and is regulated by GCNF in parallel to CRIPTO-1. Thus, our study supports the hypothesis of GCNF playing a central role during differentiation of stem cells by repression of stem cell-specific genes.
  Journal of Biological Chemistry 12/2006; 281(44):33497-504. · 4.77 Impact Factor
• Article: Mice with a targeted disruption of the Cl-/HCO3- exchanger AE3 display a reduced seizure threshold.

  Moritz Hentschke, Martin Wiemann, Suna Hentschke, Ingo Kurth, Irm Hermans-Borgmeyer, Thomas Seidenbecher, Thomas J Jentsch, Andreas Gal, Christian A Hübner
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  ABSTRACT: Neuronal activity results in significant pH shifts in neurons, glia, and interstitial space. Several transport mechanisms are involved in the fine-tuning and regulation of extra- and intracellular pH. The sodium-independent electroneutral anion exchangers (AEs) exchange intracellular bicarbonate for extracellular chloride and thereby lower the intracellular pH. Recently, a significant association was found with the variant Ala867Asp of the anion exchanger AE3, which is predominantly expressed in brain and heart, in a large cohort of patients with idiopathic generalized epilepsy. To analyze a possible involvement of AE3 dysfunction in the pathogenesis of seizures, we generated an AE3-knockout mouse model by targeted disruption of Slc4a3. AE3-knockout mice were apparently healthy, and neither displayed gross histological and behavioral abnormalities nor spontaneous seizures or spike wave complexes in electrocorticograms. However, the seizure threshold of AE3-knockout mice exposed to bicuculline, pentylenetetrazole, or pilocarpine was reduced, and seizure-induced mortality was significantly increased compared to wild-type littermates. In the pyramidal cell layer of the hippocampal CA3 region, where AE3 is strongly expressed, disruption of AE3 abolished sodium-independent chloride-bicarbonate exchange. These findings strongly support the hypothesis that AE3 modulates seizure susceptibility and, therefore, are of significance for understanding the role of intracellular pH in epilepsy.
  Molecular and Cellular Biology 02/2006; 26(1):182-91. · 5.53 Impact Factor
• Article: The forkhead transcription factor Foxi1 directly activates the AE4 promoter.

  Ingo Kurth, Moritz Hentschke, Suna Hentschke, Uwe Borgmeyer, Andreas Gal, Christian A Hübner
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  ABSTRACT: Intercalated cells are highly specialized cells within the renal collecting duct epithelium and play an important role in systemic acid-base homoeostasis. Whereas type A intercalated cells secrete protons via an apically localized H+-ATPase, type B intercalated cells secrete HCO3-. Type B intercalated cells specifically express the HCO3-/Cl- exchanger AE4 (anion exchanger 4), encoded by Slc4a9. Mice with a targeted disruption of the gene for the forkhead transcription factor Foxi1 display renal tubular acidosis due to an intercalated cell-differentiation defect. Collecting duct cells in these mice are characterized by the absence of inter-calated cell markers including AE4. To test whether Slc4a9 is a direct target gene of Foxi1, an AE4 promoter construct was generated for a cell-based reporter gene assay. Co-transfection with the Foxi1 cDNA resulted in an approx. 100-fold activation of the AE4 promoter construct. By truncating the AE4 promoter at the 5'-end, we demonstrate that a fragment of approx. 462 bp upstream of the transcription start point is sufficient to mediate activation by Foxi1. Sequence analysis of this region revealed at least eight potential binding sites for Foxi1 in both sense and antisense orientation. Only one element was bound by recombinant Foxi1 protein in bandshift assays. Mutation of this site abolished both binding in bandshift assays and transcriptional activation by co-transfection of Foxi1 in the reporter gene assay. We thus identify the AE4 promoter as a direct target of Foxi1.
  Biochemical Journal 02/2006; 393(Pt 1):277-83. · 4.90 Impact Factor