Biomedical subjects

Günther Schütz

Publications and source records attributed to Günther Schütz.

At least 19 recordsLinked to original sources

PubMed2007

Expression of Cre recombinase in dopaminoceptive neurons.

BACKGROUND: Dopamine-activated signaling regulates locomotor and emotional responses and alterations in dopamine-signaling are responsible of several psychomotor disorders. In order to identify specific functions of these pathways, the Cre/loxP system has been used. Here, we describe the generation and the characterization of a transgenic mouse line expressing the Cre recombinase in dopaminoceptive neurons. To this purpose, we used as expression vector a 140 kb yeast artificial chromosome (YAC) containing the dopamine D1 receptor gene (Drd1a). RESULTS: In the chosen line, D1Cre, the spatio-temporal pattern of Cre expression closely recapitulated that of the endogenous Drd1a gene, as assessed by immunohistological approaches in embryonic and adult stages. Efficiency of recombination was confirmed by crossing D1Cre with three different loxP lines (Creb1loxP, CaMKIVloxP and GRloxP) and with the R26R reporter. In the three loxP lines studied, recombination was restricted to the area of Cre expression. CONCLUSION: In view of the patterns of recombination restricted to the major dopaminoceptive regions as seen in the context of the CREB, CaMKIV and GR mutations, the D1Cre line will be a useful tool to dissect the contributions of specific genes to biological processes involving dopamine signaling.

Animals↗

PubMed2006

Definition of estrogen receptor pathway critical for estrogen positive feedback to gonadotropin-releasing hormone neurons and fertility.

The mechanisms through which estrogen regulates gonadotropin-releasing hormone (GnRH) neurons to control mammalian ovulation are unknown. We found that estrogen positive feedback to generate the preovulatory gonadotropin surge was normal in estrogen receptor beta knockout (ERbeta) mutant mice, but absent in ERalpha mutant mice. An ERalpha-selective compound was sufficient to generate positive feedback in wild-type mice. As GnRH neurons do not express ERalpha, estrogen positive feedback upon GnRH neurons must be indirect in nature. To establish the cell type responsible, we generated a neuron-specific ERalpha mutant mouse line. These mice failed to exhibit estrogen positive feedback, demonstrating that neurons expressing ERalpha are critical. We then used a GnRH neuron-specific Pseudorabies virus (PRV) tracing approach to show that the ERalpha-expressing neurons innervating GnRH neurons are located within rostral periventricular regions of the hypothalamus. These studies demonstrate that ovulation is driven by estrogen actions upon ERalpha-expressing neuronal afferents to GnRH neurons.

Animals↗

PubMed2006

Serum response factor controls neuronal circuit assembly in the hippocampus.

Higher organisms rely on multiple modes of memory storage using the hippocampal network, which is built by precisely orchestrated mechanisms of axonal outgrowth, guidance and synaptic targeting. We demonstrate essential roles of the transcription factor serum response factor (SRF), a sensor of cytoskeletal actin dynamics, in all these processes. Conditional deletion of the mouse Srf gene reduced neurite outgrowth and abolished mossy fiber segregation, resulting in ectopic fiber growth inside the pyramidal layer. SRF-deficient mossy fibers aberrantly targeted CA3 somata for synapse formation. Axon guidance assays showed that SRF was a key mediator of ephrin-A and semaphorin guidance cues; in SRF-deficient neurons, these resulted in the formation of F-actin-microtubule rings rather than complete growth cone collapse. Dominant-negative variants of the SRF cofactor megakaryocytic acute leukemia (MAL) severely impeded neurite outgrowth and guidance. These data highlight essential links between SRF-mediated transcription and axon guidance and circuit formation in the hippocampus.

Actins↗

PubMed2006

Forebrain-specific inactivation of Gq/G11 family G proteins results in age-dependent epilepsy and impaired endocannabinoid formation.

Metabotropic receptors coupled to Gq/G11 family G proteins critically contribute to nervous system functions by modulating synaptic transmission, often facilitating excitation. We investigated the role of Gq/G11 family G proteins in the regulation of neuronal excitability in mice that selectively lack the alpha-subunits of Gq and G11, G alpha q and G alpha 11, respectively, in forebrain principal neurons. Surprisingly, mutant mice exhibited increased seizure susceptibility, and the activation of neuroprotective mechanisms was impaired. We found that endocannabinoid levels were reduced under both basal and excitotoxic conditions and that increased susceptibility to kainic acid could be normalized by the enhancement of endocannabinoid levels with an endocannabinoid reuptake inhibitor, while the competitive cannabinoid type 1 receptor antagonist SR141716A did not cause further aggravation. These findings indicate that Gq/G11 family G proteins negatively regulate neuronal excitability in vivo and suggest that impaired endocannabinoid formation in the absence of Gq/G11 contributes to this phenotype.

Age Factors↗

PubMed2005

Loss of the limbic mineralocorticoid receptor impairs behavioral plasticity.

Corticosteroid action in the brain is mediated by the mineralocorticoid (MR) and the glucocorticoid (GR) receptor. Disturbances in MR- and GR-mediated effects are thought to impair cognition, behavior, and endocrine control. To assess the function of the limbic MR in these processes, we inactivated the MR gene in the forebrain of the mouse using the Cre/loxP-recombination system. We screened the mice with a limbic MR deficiency in various learning and exploration tests. The mutant mice show impaired learning of the water-maze task and deficits in measures of working memory on the radial maze due to behavioral perseverance and stereotypy. They exhibit a hyperreactivity toward a novel object but normal anxiety-like behavior. The behavioral changes are associated with abnormalities of the mossy fiber projection and an up-regulation of GR expression in the hippocampus. Adult mutant mice show normal corticosterone levels at circadian trough and peak. This genetic model provides important information about the consequences of a permanently altered balance between limbic MR and GR, with implications for stress-related neuroendocrine and neuropsychiatric diseases.

Animals↗

PubMed2005

Mineralocorticoid receptors are indispensable for nongenomic modulation of hippocampal glutamate transmission by corticosterone.

The adrenal hormone corticosterone transcriptionally regulates responsive genes in the rodent hippocampus through nuclear mineralocorticoid and glucocorticoid receptors. Via this genomic pathway the hormone alters properties of hippocampal cells slowly and for a prolonged period. Here we report that corticosterone also rapidly and reversibly changes hippocampal signaling. Stress levels of the hormone enhance the frequency of miniature excitatory postsynaptic potentials in CA1 pyramidal neurons and reduce paired-pulse facilitation, pointing to a hormone-dependent enhancement of glutamate-release probability. The rapid effect by corticosterone is accomplished through a nongenomic pathway involving membrane-located receptors. Unexpectedly, the rapid effect critically depends on the classical mineralocorticoid receptor, as evidenced by the effectiveness of agonists, antagonists, and brain-specific inactivation of the mineralocorticoid but not the glucocorticoid receptor gene. Rapid actions by corticosterone would allow the brain to change its function within minutes after stress-induced elevations of corticosteroid levels, in addition to responding later through gene-mediated signaling pathways.

Adrenal Cortex Hormones↗

PubMed2005

Target-dependent specification of the neurotransmitter phenotype: cholinergic differentiation of sympathetic neurons is mediated in vivo by gp 130 signaling.

Sympathetic neurons are generated through a succession of differentiation steps that initially lead to noradrenergic neurons innervating different peripheral target tissues. Specific targets, like sweat glands in rodent footpads, induce a change from noradrenergic to cholinergic transmitter phenotype. Here, we show that cytokines acting through the gp 130 receptor are present in sweat glands. Selective elimination of the gp 130 receptor in sympathetic neurons prevents the acquisition of cholinergic and peptidergic features (VAChT, ChT1, VIP) without affecting other properties of sweat gland innervation. The vast majority of cholinergic neurons in the stellate ganglion, generated postnatally, are absent in gp 130-deficient mice. These results demonstrate an essential role of gp 130-signaling in the target-dependent specification of the cholinergic neurotransmitter phenotype.

Adrenergic Fibers↗

PubMed2005

cAMP response element-binding protein regulates differentiation and survival of newborn neurons in the olfactory bulb.

The transcription factor cAMP response element-binding protein (CREB) is involved in multiple aspects of neuronal development and plasticity. Here, we demonstrate that CREB regulates specific phases of adult neurogenesis in the subventricular zone/olfactory bulb (SVZ/OB) system. Combining immunohistochemistry with bromodeoxyuridine treatments, cell tracer injections, cell transplants, and quantitative analyses, we show that although CREB is expressed by the SVZ neuroblasts throughout the neurogenic process, its phosphorylation is transient and parallels neuronal differentiation, increasing during the late phase of tangential migration and decreasing after dendrite elongation and spine formation. In vitro, inhibition of CREB function impairs morphological differentiation of SVZ-derived neuroblasts. Transgenic mice lacking CREB, in a null CREM genetic background, show reduced survival of newborn neurons in the OB. This finding is further supported by peripheral afferent denervation experiments resulting in downregulation of CREB phosphorylation in neuroblasts, the survival of which appears heavily impaired. Together, these findings provide evidence that CREB regulates differentiation and survival of newborn neurons in the OB.

Animals↗

PubMed2005

Hypothalamic 3',5'-cyclic adenosine monophosphate response element-binding protein loss causes anterior pituitary hypoplasia and dwarfism in mice.

The principal regulation of body growth is via a cascade of hormone signals emanating from the hypothalamus, by release of GHRH, which then directs the somatotroph cells of the pituitary to release GH into the blood stream. This in turn leads to activation of signal transducer and activator of transcription 5-dependent expression of genes such as IGF-I in hepatocytes, acid labile substance, and serine protease inhibitor 2.1, resulting in body growth. Here, using conditional cAMP response element binding protein (CREB) mutant mice, we show that loss of the CREB transcription factor in the brain, but not the pituitary, results in reduced postnatal growth consistent with dwarfism caused by GH deficiency. We demonstrate that although there appears to be no significant impact upon the expression of GHRH mRNA in CREB mutant mice, the amount of GHRH peptide is reduced. These findings show that CREB is required for the efficient production of GHRH in hypothalamus, in addition to its previously reported role in pituitary GH production and somatotroph expansion.

Animals↗

PubMed2005

Mice with genetically altered glucocorticoid receptor expression show altered sensitivity for stress-induced depressive reactions.

Altered glucocorticoid receptor (GR) signaling is a postulated mechanism for the pathogenesis of major depression. To mimic the human situation of altered GR function claimed for depression, we generated mouse strains that underexpress or overexpress GR, but maintain the regulatory genetic context controlling the GR gene. To achieve this goal, we used the following: (1) GR-heterozygous mutant mice (GR+/-) with a 50% GR gene dose reduction, and (2) mice overexpressing GR by a yeast artificial chromosome resulting in a twofold gene dose elevation. GR+/- mice exhibit normal baseline behaviors but demonstrate increased helplessness after stress exposure, a behavioral correlate of depression in mice. Similar to depressed patients, GR+/- mice have a disinhibited hypothalamic-pituitary-adrenal (HPA) system and a pathological dexamethasone/corticotropin-releasing hormone test. Thus, they represent a murine depression model with good face and construct validity. Overexpression of GR in mice evokes reduced helplessness after stress exposure, and an enhanced HPA system feedback regulation. Therefore, they may represent a model for a stress-resistant strain. These mouse models can now be used to study biological changes underlying the pathogenesis of depressive disorders. As a first potential molecular correlate for such changes, we identified a downregulation of BDNF protein content in the hippocampus of GR+/- mice, which is in agreement with the so-called neurotrophin hypothesis of depression.

Animals↗

PubMed2005

SRF mediates activity-induced gene expression and synaptic plasticity but not neuronal viability.

Synaptic activity-dependent gene expression is critical for certain forms of neuronal plasticity and survival in the mammalian nervous system, yet the mechanisms by which coordinated regulation of activity-induced genes supports neuronal function is unclear. Here, we show that deletion of serum response factor (SRF) in specific neuronal populations in adult mice results in profound deficits in activity-dependent immediate early gene expression, but components of upstream signaling pathways and cyclic AMP-response element binding protein (CREB)-dependent transactivation remain intact. Moreover, SRF-deficient CA1 pyramidal neurons show attenuation of long-term synaptic potentiation, a model for neuronal information storage. Furthermore, in contrast to the massive neurodegeneration seen in adult mice lacking CREB family members, SRF-deficient adult neurons show normal morphologies and basal excitatory synaptic transmission. These findings indicate that the transcriptional events underlying neuronal survival and plasticity are dissociable and that SRF plays a prominent role in use-dependent modification of synaptic strength in the adult brain.

Animals↗

PubMed2005

Neuronal migration in the murine rostral migratory stream requires serum response factor.

The central nervous system is fundamentally dependent on guided cell migration, both during development and in adulthood. We report an absolute requirement of the transcription factor serum response factor (SRF) for neuronal migration in the mouse forebrain. Conditional, late-prenatal deletion of Srf causes neurons to accumulate ectopically at the subventricular zone (SVZ), a prime neurogenic region in the brain. SRF-deficient cells of the SVZ exhibit impaired tangential chain migration along the rostral migratory stream into the olfactory bulb. SVZ explants display retarded chain migration in vitro. Regarding target genes, SRF deficiency impairs expression of the beta-actin and gelsolin genes, accompanied by reduced cytoskeletal actin fiber density. At the posttranslational level, cofilin, a key regulator of actin dynamics, displays dramatically elevated inhibitory phosphorylation at Ser-3. Our studies indicate that SRF-controlled gene expression directs both the structure and dynamics of the actin microfilament, thereby determining cell-autonomous neuronal migration.

Actins↗

PubMed2005

Glucocorticoids inhibit activation-induced cell death (AICD) via direct DNA-dependent repression of the CD95 ligand gene by a glucocorticoid receptor dimer.

Glucocorticoids (GCs) play an important role in the regulation of peripheral T-cell survival. Their molecular mechanism of action and the question of whether they have the ability to inhibit apoptosis in vivo, however, are not fully elucidated. Signal transduction through the glucocorticoid receptor (GR) is complex and involves different pathways. Therefore, we used mice with T-cell-specific inactivation of the GR as well as mice with a function-selective mutation in the GR to determine the signaling mechanism. Evidence is presented for a functional role of direct binding of the GR to 2 negative glucocorticoid regulatory elements (nGREs) in the CD95 (APO-1/Fas) ligand (L) promoter. Binding of GRs to these nGREs reduces activation-induced CD95L expression in T cells. These in vitro results are fully supported by data obtained in vivo. Administration of GCs to mice leads to inhibition of activation-induced cell death (AICD). Thus, GC-mediated inhibition of CD95L expression of activated T cells might contribute to the anti-inflammatory function of steroid drugs.

Animals↗

PubMed2005

Evaluation of steroid receptor function by gene targeting in mice.

Corticosteroid hormones regulate a variety of developmental, physiological and pathological processes via their cognate receptors, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). Using modern genetic technologies, including bacterial artificial chromosome-based transgenesis and conditional gene targeting, we have generated a panel of tissue-specific and function-selective mutations of the two corticosteroid hormone receptors in the mouse. These mouse models have allowed us to gain new insights into corticosteroid hormone signaling in vivo. By investigating a hepatocyte-specific GR mutation, it has been possible to define a novel biological action of GR, namely to function as a coactivator for Stat5-mediated gene transcription in the control of body growth. The investigation of brain-specific mutations have not only allowed us to better understand hypothalamo-pituitary-adrenal (HPA) axis regulation by glucocorticoids, but also to analyse corticosteroid action in various aspects of brain function like anxiety-related or addiction-related behaviour, and learning and memory. A function-selective mutation in the GR has allowed us to dissect different pathways in the gene expression regulation by this receptor, namely to separate DNA response element-binding dependent gene activation from response element-independent gene regulation via interference with other transcription factors. These different transcriptional activities of GR play an important role in glucocorticoid-mediated immunosuppression.

Alleles↗

PubMed2004

Pulmonary hypertension and right heart failure in pituitary adenylate cyclase-activating polypeptide type I receptor-deficient mice.

BACKGROUND: Pituitary adenylate cyclase-activating polypeptide (PACAP), acting via 3 different G protein-coupled receptors, has been implicated in the regulation of several homeostatic systems in the body, including cardiopulmonary control. To define the physiologic role of the PACAP-preferring type I receptor, PAC1, in cardiopulmonary function, we developed a mutant mouse strain lacking functional PAC1 receptors. METHODS AND RESULTS: When PAC1-deficient mice were crossed onto a C57BL/6 background, almost all mutants died during the second postnatal week. Whereas mutant mice were indistinguishable from their wild-type littermates at birth, they showed progressive weakness and died from rapidly developing heart failure. Right ventricles of PAC1 mutants were massively dilated and showed cardiac myocyte hypertrophy, whereas left ventricular structure was unaltered. On direct cardiac catheterization, right ventricular pressure was elevated by 45% in PAC1-deficient mice, indicating increased pulmonary artery pressure, as no malformations were detected in the valves or outflow tract of the right ventricle. Consistent with elevated pulmonary pressure, lung capillary density was decreased by 30% and small pulmonary arteries of mutant mice had significant vascular smooth muscle cell hypertrophy compared with wild-type mice. CONCLUSIONS: Whereas PACAP induces vasodilation in isolated pulmonary vessels in wild-type mice, the absence of its specific receptor PAC1 causes pulmonary hypertension and right heart failure after birth. These in vivo findings demonstrate the crucial importance of PAC1-mediated signaling for the maintenance of normal pulmonary vascular tone during early postnatal life.

Animals↗

PubMed2004

The epithelial glucocorticoid receptor is required for the normal timing of cell proliferation during mammary lobuloalveolar development but is dispensable for milk production.

Glucocorticoids have been shown to influence mammary gland function in vivo and to stimulate milk protein gene expression in vitro. Here, we describe the generation and analysis of a mouse model to study glucocorticoid receptor (GR, NR3C1) function in mammary epithelial cells. Using the Cre-loxP system, mutant mice were obtained in which the GR gene is specifically deleted in epithelial cells during lobuloalveolar development, leading to a complete loss of epithelial GR at the onset of lactation. Mice harboring the mammary-epithelial-specific GR mutation are able to nurse their litters until weaning. During pregnancy, however, GR deficiency delays lobuloalveolar development, leading to an incomplete epithelial penetration of the mammary fat pad that persists throughout lactation. We identified a reduced cell proliferation during lobuloalveolar development as reason for this delay. This reduction is compensated for by increased epithelial proliferation after parturition in the mutant glands. During lactation, GR-deficient mammary epithelium is capable of milk production and secretion. The expression of two milk proteins, namely whey acidic protein and beta-casein, during lactation was not critically affected in the absence of GR. We conclude that GR function is not essential for alveolar differentiation and milk production, but influences cell proliferation during lobuloalveolar development.

Alleles↗

PubMed2004

Reduced expression of brain-derived neurotrophic factor in mice deficient for pituitary adenylate cyclase activating polypeptide type-I-receptor.

In vitro pituitary adenylate cyclase activating polypeptide (PACAP) induces the expression of brain-derived neurotrophic factor (BDNF) via its specific receptor PAC1. Since BDNF has been implicated in learning paradigms and mice lacking functional PAC1 have deficits in hippocampus-dependent associative learning, we investigated whether PAC1 mutants show alterations in hippocampal expression of BDNF and its receptor TrkB. Semi-quantitative in situ-hybridization using exon-specific BDNF-probes revealed significantly reduced expression of the exon-III and exon-V-specific transcripts within the hippocampal CA3 region in PAC1-deficient mice. A similar trend was observed for the exon-I-specific transcript. The expression of the exon-III-specific transcript was also reduced within the dentate gyrus, while Trk B-expression did not differ between genotypes. Our data demonstrate that even in vivo PAC1-mediated signaling seems to play a pivotal role for the transcriptional regulation of BDNF.

Animals↗

PubMed2004

Inactivation of the glucocorticoid receptor in hepatocytes leads to fasting hypoglycemia and ameliorates hyperglycemia in streptozotocin-induced diabetes mellitus.

Hepatic glucose production by gluconeogenesis is the main source of glucose during fasting and contributes significantly to hyperglycemia in diabetes mellitus. Accordingly, glucose metabolism is tightly controlled by a variety of hormones including insulin, epinephrine, glucagon, and glucocorticoids (GCs) acting on various cell types. GC effects are mediated by the GC receptor (GR), a ligand-dependent transcription factor, which in the liver and kidney controls gluconeogenesis by induction of gluconeogenic enzymes. To specifically study the contribution of GC on liver carbohydrate metabolism, we generated mice with an inactivation of the GR gene exclusively in hepatocytes using the Cre/loxP technology. Half of the mutant mice die within the first 2 d after birth most likely due to hypoglycemia. Adult mice have normal blood sugar under basal conditions but show hypoglycemia after prolonged starvation due to reduced expression of genes involved in gluconeogenesis. We further demonstrate that absence of GR in hepatocytes limits the development of hyperglycemia in streptozotocin-induced diabetes mellitus probably due to impaired induction of gluconeogenesis. These findings show the essential role of GR function in liver glucose metabolism during fasting and in diabetic mice and indicate that liver-specific GC antagonists could be beneficial in control of diabetic hyperglycemia.

Animals↗