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Klaus H Kaestner

Publications and source records attributed to Klaus H Kaestner.

15 recordsLinked to original sources
PubMed2025

G6PC2 controls glucagon secretion by defining the set point for glucose in pancreatic α cells.

Elevated glucagon concentrations have been reported in patients with type 2 diabetes (T2D). A critical role for α cell-intrinsic mechanisms in regulating glucagon secretion was previously established through genetic manipulation of the glycolytic enzyme glucokinase (GCK) in mice. Genetic variation at the glucose-6-phosphatase catalytic subunit 2 (G6PC2) locus, encoding an enzyme that opposes GCK, has been reproducibly associated with fasting blood glucose and hemoglobin A1c. Here, we found that trait-associated variants in the G6PC2 promoter are located in open chromatin not just in β but also in α cells and documented allele-specific G6PC2 expression of linked variants in human α cells. Using α cell-specific gene ablation of G6pc2 in mice, we showed that this gene plays a critical role in controlling glucose suppression of amino acid-stimulated glucagon secretion independent of alterations in insulin output, islet hormone content, or islet morphology, findings that we confirmed in primary human α cells. Collectively, our data demonstrate that G6PC2 affects glycemic control via its action in α cells and possibly suggest that G6PC2 inhibitors might help control blood glucose through a bihormonal mechanism.

Glucagon↗
PubMed2003

Hepatocyte nuclear factor 4alpha controls the development of a hepatic epithelium and liver morphogenesis.

Although advances have been made in understanding cell differentiation, only rudimentary knowledge exists concerning how differentiated cells form tissues and organs. We studied liver organogenesis because the cell and tissue architecture of this organ is well defined. Approximately 60% of the adult liver consists of hepatocytes that are arranged as single-cell anastomosing plates extending from the portal region of the liver lobule toward the central vein. The basal surface of the hepatocytes is separated from adjacent sinusoidal endothelial cells by the space of Disse, where the exchange of substances between serum and hepatocytes takes place. The hepatocyte's apical surface forms bile canaliculi that transport bile to the hepatic ducts. Proper liver architecture is crucial for hepatic function and is commonly disrupted in disease states, including cirrhosis and hepatitis. Here we report that hepatocyte nuclear factor 4alpha (Hnf4alpha) is essential for morphological and functional differentiation of hepatocytes, accumulation of hepatic glycogen stores and generation of a hepatic epithelium. We show that Hnf4alpha is a dominant regulator of the epithelial phenotype because its ectopic expression in fibroblasts induces a mesenchymal-to-epithelial transition. Most importantly, the morphogenetic parameters controlled by Hnf4alpha in hepatocytes are essential for normal liver architecture, including the organization of the sinusoidal endothelium.

Animals↗
PubMed2003

Transcriptional program of the endocrine pancreas in mice and humans.

The Endocrine Pancreas Consortium was formed in late 1999 to derive and sequence cDNA libraries enriched for rare transcripts expressed in the mammalian endocrine pancreas. Over the past 3 years, the Consortium has generated 20 cDNA libraries from mouse and human pancreatic tissues and deposited >150,000 sequences into the public expressed sequence tag databases. A special effort was made to enrich for cDNAs from the endocrine pancreas by constructing libraries from isolated islets. In addition, we constructed a library in which fetal pancreas from Neurogenin 3 null mice, which consists of only exocrine and duct cells, was subtracted from fetal wild-type pancreas to enrich for the transcripts from the endocrine compartment. Sequence analysis showed that these clones cluster into 9,464 assembly groups (approximating unique transcripts) for the mouse and 13,910 for the human sequences. Of these, >4,300 were unique to Consortium libraries. We have assembled a core clone set containing one cDNA for each assembly group for the mouse and have constructed the corresponding microarray, termed "PancChip 4.0," which contains >9,000 nonredundant elements. We show that this PancChip is highly enriched for genes expressed in the endocrine pancreas. The mouse and human clone sets and corresponding arrays will be important resources for diabetes research.

Animals↗
PubMed2002

Comparison of different labeling methods for two-channel high-density microarray experiments.

In this report we evaluate three methods for labeling nucleic acids to be hybridized to a cDNA microarray: direct labeling, indirect amino-allyl labeling, and the dendrimer labeling method (Genisphere). The dendrimer method requires the smallest quantity of sample, 2.5 microg of total RNA compared with 20 microg with the direct or indirect methods. Therefore, we wanted to know whether the performance of the dendrimer method is comparable to the other methods, or whether significant information is lost. Performance can be considered in terms of sensitivity, dynamic range, and reproducibility of the quantitative signals for gene intensity. We compared the three labeling methods by generating three sets of eight self-to-self hybridizations using the same total RNA sample in all cases ("replicate study"). In our analysis, we controlled for the effects of print-tip and background subtraction biases. We also performed a smaller study, namely, a dilution series study with five dilution points per labeling method, to evaluate one aspect of predictive ability. From the replicate study, the dendrimer method appeared to perform as well, and often better, with respect to reproducibility and ability to detect expression. However, in the dilution series study, this method was outperformed by the other two in terms of predictive ability and did not perform very well. These findings are helping to guide our decisions on what labeling method to use for subsequent studies, based on the purpose of a specific study and its limitations in terms of available material.

Fluorescent Dyes↗
PubMed2002

Foxa3 (HNF-3gamma) binds to and activates the rat proglucagon gene promoter but is not essential for proglucagon gene expression.

Members of the Forkhead box a (Foxa) transcription factor family are expressed in the liver, pancreatic islets and intestine and both Foxa1 and Foxa2 regulate proglucagon gene transcription. As Foxa proteins exhibit overlapping DNA-binding specificities, we examined the role of Foxa3 [hepatocyte nuclear factor (HNF)-3gamma] in control of proglucagon gene expression. Foxa3 was detected by reverse transcriptase PCR in glucagon-producing cell lines and binds to the rat proglucagon gene G2 promoter element in GLUTag enteroendocrine cells. Although Foxa3 increased rat proglucagon promoter activity in BHK fibroblasts, augmentation of Foxa3 expression did not increase proglucagon promoter activity in GLUTag cells. Furthermore, adenoviral Foxa3 expression did not affect endogenous proglucagon gene expression in islet or intestinal endocrine cell lines. Although Foxa3(-/-) mice exhibit mild hypoglycaemia during a prolonged fast, the levels of proglucagon-derived peptides and proglucagon mRNA transcripts were comparable in tissues from wild-type and Foxa3(-/-) mice. These findings identify Foxa3 as a member of the proglucagon gene G2 element binding-protein family that, unlike Foxa1, is not essential for control of islet or intestinal proglucagon gene expression in vivo.

Animals↗
PubMed2002

Neurogenin 3 is essential for the proper specification of gastric enteroendocrine cells and the maintenance of gastric epithelial cell identity.

The notch signaling pathway is essential for the endocrine cell fate in various tissues including the enteroendocrine system of the gastrointestinal tract. Enteroendocrine cells are one of the four major cell types found in the gastric epithelium of the glandular stomach. To understand the molecular basis of enteroendocrine cell development, we have used gene targeting in mouse embryonic stem cells to derive an EGFP-marked null allele of the bHLH transcription factor, neurogenin 3 (ngn3). In ngn3(-/-) mice, glucagon secreting A-cells, somatostatin secreting D-cells, and gastrin secreting G-cells are absent from the epithelium of the glandular stomach, whereas the number of serotonin-expressing enterochromaffin (EC) cells is decreased dramatically. In addition, ngn3(-/-) mice display intestinal metaplasia of the gastric epithelium. Thus, ngn3 is required for the differentiation of enteroendocrine cells in the stomach and the maintenance of gastric epithelial cell identity.

Alleles↗
PubMed2002

Maintenance of the specification of the anterior definitive endoderm and forebrain depends on the axial mesendoderm: a study using HNF3beta/Foxa2 conditional mutants.

In mouse embryo, the early induction of the head region depends on signals from the anterior visceral endoderm (AVE) and the anterior primitive streak. Subsequently, node derivatives, including anterior definitive endoderm and axial mesendoderm, are thought to play a role in the maintenance and elaboration of anterior neural character. Foxa2 encodes a winged-helix transcription factor expressed in signaling centers required for head development, including the AVE, anterior primitive streak, anterior definitive endoderm, and axial mesendoderm. To address Foxa2 function during formation of the head, we used conditional mutants in which Foxa2 function is preserved in extraembryonic tissues during early embryonic stages and inactivated in embryonic tissues after the onset of gastrulation. In Foxa2 conditional mutants, the anterior neural plate and anterior definitive endoderm were initially specified. In contrast, the axial mesendoderm failed to differentiate. At later stages, specification of the anterior neural plate and anterior definitive endoderm was shown to be labile. As a result, head truncations were observed in Foxa2 conditional mutants. Our results therefore indicate that anterior definitive endoderm alone is not sufficient to maintain anterior head specification and that an interaction between the axial mesendoderm and the anterior definitive endoderm is required for proper specification of the endoderm. Foxa2 therefore plays an integral role in the formation of axial mesendoderm, which is required to maintain the specification of the forebrain and the anterior definitive endoderm.

Animals↗
PubMed2002

Cellular and molecular mechanisms of carcinogenesis.

Our understanding of the cellular and molecular mechanisms of cancer of the gastrointestinal tract has increased dramatically over the last several decades. We are identifying new players in the pathways toward cancer with increasing frequency. In addition, we have come to understand that no single pathway acts by itself; in vivo, the effects are combinatorial. As new and better cell culture and animal models of carcinogenesis arise, our knowledge will continue to grow. As we learn more, we will be able to translate the results of our research into new and better techniques for the diagnosis and treatment of gastrointestinal cancers.

Apoptosis↗
PubMed2002

Developmental and cell type-specific expression of the zinc finger transcription factor Krüppel-like factor 4 (Klf4) in postnatal mouse testis.

The transcription factor Krüppel-like factor 4 (Klf4, formerly gut-enriched Krüppel-like factor, GKLF) is specifically expressed in postproliferative epithelial cells such as those of the gut and the epidermis. The importance of Klf4 in terminal differentiation of keratinocytes has been demonstrated by targeted gene ablation in mice. Klf4-deficient mice fail to establish the barrier function of the skin and die shortly after birth due to dehydration. Based on these findings as well as in vitro studies, Klf4 was characterized as a transcription factor essential for postproliferative differentiation of epithelial cells. However, the testicular Klf4 expression pattern is completely unknown. Here, we demonstrate that Klf4 is developmentally regulated during postnatal testicular development of the mouse. Furthermore, we show strong expression in the postmeiotic germ cells undergoing final differentiation into sperm cells and provide evidence that Klf4 is also expressed in the somatic Sertoli cells. These findings suggest that Klf4 might play an important role in testicular differentiation in mammals.

Animals↗
PubMed2002

Cdx2 ectopic expression induces gastric intestinal metaplasia in transgenic mice.

BACKGROUND & AIMS: Intestinal-type gastric cancer is often preceded by intestinal metaplasia in humans. The genetic events responsible for the transdifferentiation that occurs in intestinal metaplasia are not well understood. Cdx2, a transcription factor whose expression is normally limited to the intestine, has been detected in gastric intestinal metaplasia. Cdx2 induces differentiation of intestinal epithelial cells in vitro; therefore, we sought to establish whether a causal relationship exists between Cdx2 activation and intestinal metaplasia. METHODS: Cdx2 expression was directed to the gastric mucosa in transgenic mice using cis-regulatory elements of Foxa3 (Hnf3gamma). Transgenic mice were analyzed for histologic and gene expression changes. RESULTS: Histologic examination of the gastric mucosa of the Foxa3/Cdx2 mice revealed the presence of alcian blue-positive intestinal-type goblet cells, a hallmark of intestinal metaplasia. In addition, Cdx2 induced the expression of intestine-specific genes. CONCLUSIONS: Gastric expression of Cdx2 alone was sufficient to induce intestinal metaplasia in mice. These mice represent a powerful tool to investigate the molecular mechanisms that promote intestinal metaplasia. Moreover, as gastric cancer in humans is often preceded by intestinal metaplasia, the phenotype described here strongly suggests involvement of Cdx2 in the initiation of the process leading to intestinal neoplasia of the gastric mucosa.

Animals↗
PubMed2002

The role of the receptor tyrosine kinase Ron in nickel-induced acute lung injury.

Acute lung injury (ALI), a severe respiratory syndrome, develops in response to numerous insults and responds poorly to therapeutic intervention. Recently, cDNA microarray analyses were performed that indicated several pathogenic responses during nickel-induced ALI, including marked macrophage activation. Macrophage activation is mediated, in part, via the receptor tyrosine kinase Ron. To address the role of Ron in ALI, the response of mice deficient in the cytoplasmic domain of Ron (Ron tk-/-) were assessed in response to nickel exposure. Ron tk-/- mice succumb to nickel-induced ALI earlier, express larger, early increases in interleukin-6, monocyte chemoattractant protein-1, and macrophage inflammatory protein-2, display greater serum nitrite levels, and exhibit earlier onset of pulmonary pathology and augmented pulmonary tyrosine nitrosylation. Increases in cytokine expression and cellular nitration can lead to tissue damage and are consistent with the differences between genotypes in the early onset of pathology and mortality in Ron tk-/- mice. These analyses indicate a role for the tyrosine kinase receptor Ron in ALI.

Androstadienes↗
PubMed2002

The zinc-finger transcription factor Klf4 is required for terminal differentiation of goblet cells in the colon.

Klf4 (formerly GKLF) is a zinc-finger transcription factor expressed in the epithelia of the skin, lungs, gastrointestinal tract and several other organs. In vitro studies have suggested that Klf4 plays an important role in cell proliferation and/or differentiation. Mice homozygous for a null mutation in Klf4 die within 15 hours of birth and show selective perturbation of late-stage differentiation structures in the epidermis, but the function of Klf4 in the gastrointestinal tract has not been investigated. To address this issue, we have generated Klf4(-/-) mice by homologous recombination in embryonic stem cells. In this study, we provide the first in vivo evidence that Klf4 is a goblet cell-specific differentiation factor in the colon. Klf4(-/-) mice exhibit normal cell proliferation and cell death rates in the colon on postnatal day 1. However, Klf4(-/-) mice demonstrate a 90% decrease in the number of goblet cells in the colon, show abnormal expression of the goblet cell-specific marker Muc2 by in situ hybridization, have abnormal staining of the colonic epithelium with Alcian Blue for acidic mucins, and lack normal goblet cell morphology by ultrastructural analysis. All other epithelial cell types are present in the colon of Klf4(-/-) mice. In summary, Klf4 plays a crucial role in colonic epithelial cell differentiation in vivo.

Animals↗
PubMed2002

Functional genomics of the endocrine pancreas: the pancreas clone set and PancChip, new resources for diabetes research.

Over the past 5 years, microarrays have greatly facilitated large-scale analysis of gene expression levels. Although these arrays were not specifically geared to represent tissues and pathways known to be affected by diabetes, they have been used in both type 1 and type 2 diabetes research. To prepare a tool that is particularly useful in the study of type 1 diabetes, we have assembled a nonredundant set of 3,400 clones representing genes expressed in the mouse pancreas or pathways known to be affected by diabetes. We have demonstrated the usefulness of this clone set by preparing a cDNA glass microarray, the PancChip, and using it to analyze pancreatic gene expression from embryonic day 14.5 through adulthood in mice. The clone set and corresponding array are useful resources for diabetes research.

Adult↗
PubMed2002

Foxa2 controls Pdx1 gene expression in pancreatic beta-cells in vivo.

Differentiation of early foregut endoderm into pancreatic endocrine and exocrine cells depends on a cascade of gene activation events controlled by various transcription factors. Prior in vitro analysis has suggested that the forkhead/winged helix transcription factor Foxa2 (formerly HNF-3beta) is a major upstream regulator of Pdx1, a homeobox gene essential for pancreatic development. Pdx1 is also essential for the maintenance of glucose homeostasis, as its human orthologue, IPF-1, is mutated in a subset of patients with early-onset type 2 diabetes (MODY4). To analyze the Foxa2/Pdx1 regulatory cascade during pancreatic beta-cell differentiation, we used conditional gene ablation of Foxa2 in mice. We demonstrated that the deletion of Foxa2 in beta-cell-specific knockout mice results in downregulation of Pdx1 mRNA and subsequent reduction of PDX-1 protein levels in islets. These data represent the first in vivo demonstration that Foxa2 acts upstream of Pdx1 in the differentiated beta-cell.

Animals↗