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K Kaupmann

Publications and source records attributed to K Kaupmann.

At least 37 records · Page 2Linked to original sources
PubMed1998

Mapping, genomic structure, and polymorphisms of the human GABABR1 receptor gene: evaluation of its involvement in idiopathic generalized epilepsy.

Neurophysiological and pharmacological studies suggest a major role of the GABAB receptor in the epileptogenesis of absence seizures. The gene encoding the human GABABR1 receptor (GABABR1) has recently been mapped to human chromosome 6p21.3 by in situ hybridization, a region that harbors a susceptibility locus (EJM1) for idiopathic generalized epilepsy (IGE). We investigated the hypothesis that the GABABR1 gene (GABBR1) represents a candidate gene for EJM1 by: (1) defining the precise localization approximately 130 kilobases telomeric to the HLA-F locus, (2) by characterizing its genomic organization, and (3) by mutation screening of the entire coding region of GABBR1 in 18 German patients with juvenile myoclonic epilepsy (JME) who were derived from families with evidence for linkage to chromosome 6p21.3 (cumulative lod score Z=3.17 at HLA-DQ). The GABAB receptor gene consists of 22 translated exons. The two alternative transcripts, GABABR1a and GABABR1b, are derived from the same locus but they differ in their alternative 5'-exons. Mutation analyses in JME revealed several DNA sequence polymorphisms, two of which result in amino acid changes occurring in all IGE-affected members of two families. However, clinically unaffected relatives did carry the same variations, excluding these amino acid substitutions as the cause for IGE in these families.

Amino Acid Substitution↗
PubMed1998

GABAB receptors: drugs meet clones.

Recently, the long-awaited cloning of the GABAB receptors, the last of the major known neurotransmitter receptors to be identified, has been reported. In addition to an emerging molecular understanding, there have been advances in discerning the specific coupling partners of GABAB receptors in the brain.

Baclofen↗
PubMed1997

Expression cloning of GABA(B) receptors uncovers similarity to metabotropic glutamate receptors.

GABA (gamma-amino-butyric acid), the principal inhibitory neurotransmitter in the brain, signals through ionotropic (GABA(A)/ GABA(c)) and metabotropic (GABA(B)) receptor systems. Here we report the cloning of GABA(B) receptors. Photoaffinity labelling experiments suggest that the cloned receptors correspond to two highly conserved GABA(B) receptor forms present in the vertebrate nervous system. The cloned receptors negatively couple to adenylyl cyclase and show sequence similarity to the metabotropic receptors for the excitatory neurotransmitter L-glutamate.

Adenylyl Cyclases↗
PubMed1995

Pharmacological identity between somatostatin SS-2 binding sites and SSTR-1 receptors.

Somatostatin (SRIF) SS-2 binding sites were originally defined in rat brain cerebral cortex membranes using [125I]Tyr11-SRIF-14 in the presence of 120 mM NaCl. These sites were characterized by their high affinity for SRIF-14 and SRIF-28, but very low affinity for cyclic peptides such as octreotide (SMS 201-995) and seglitide (MK 678). The characteristics of SS-2 sites are reminiscent of 125I]CGP 23996-labelled sites in rat brain which have been termed SRIF-2 sites. In the present study, the pharmacological profile of SS-2 sites was determined in radioligand binding studies performed in rat cortex membranes using [125I]SRIF-14 in the presence of 120 mM NaCl and compared to that of human SSTR-1 receptors expressed in human embryonic kidney (HEK 293) cells, using [125I]SRIF-14. The rank orders of affinity of a variety of SRIF analogues and synthetic peptides for SS-2 binding sites and recombinant human SSTR-1 receptors were very similar and correlated highly significantly (r = 0.99). However, SS-2 binding correlated also with binding to recombinant SSTR-4 receptors (r = 0.91). Autoradiographic studies were performed using the radioligand [125I]CGP 23996 which has been claimed to label selectively SRIF-2 binding sites and compared with the distribution of SSTR-1 receptor mRNA determined using in situ hybridization in rat brain. Although some overlap was observed between the distribution of SSTR-1 mRNA and [125I]CGP 23996 binding sites, the latter were clearly more widespread, suggesting this ligand to label SSTR-1 and other sites. In addition, inhibition of forskolin-stimulated adenylate cyclase was investigated in HEK 293 cells transfected with human SSTR-1 receptors; a variety of SRIF analogues and short synthetic peptides behaved as agonists at adenylate cyclase and displayed a rank order of potency highly similar to that observed for these compounds at SS-2 binding sites. Seglitide acted as an antagonist at SSTR-1 receptor mediated inhibition of adenylate cyclase activity with a pKB of 4.42. It is concluded that the pharmacological profile of SS-2 binding sites resembles most closely that of SSTR-1 receptors (although similarities with SSTR-4 receptors were observed), that [125I]CGP 23996 labels presumably several SRIF receptors in rat brain, and that SSTR-1 receptors are negatively and efficiently coupled to adenylate cyclase activity.

Adenylyl Cyclases↗
PubMed1995

Two amino acids, located in transmembrane domains VI and VII, determine the selectivity of the peptide agonist SMS 201-995 for the SSTR2 somatostatin receptor.

Human somatostatin receptor subtypes (SSTR1-5) bind their natural ligands SRIF-14 and SRIF-28 with high affinity. By contrast, short synthetic SRIF analogues such as SMS 201-995, a peptide agonist used for the treatment of various endocrine and malignant disorders, display sub-nanomolar affinity only for the receptor subtype SSTR2. To understand the molecular nature of selective peptide agonist binding to somatostatin receptors we have now, by site-directed mutagenesis, identified amino acids mediating SMS 201-995 specificity for SSTR2. Sequentially, amino acids in SSTR1, a receptor subtype exhibiting low affinity for SMS 201-995, were exchanged for the corresponding SSTR2 residues. After three consecutive steps, in which eight amino acids were exchanged, a SSTR1 mutant receptor with high affinity for SMS 201-995 was obtained. Receptor mutants with different combinations of these eight amino acids were then constructed. A single Ser305 to Phe mutation in TM VII increased the affinity of SSTR1 for SMS 201-995 nearly 100-fold. When this mutation was combined with an exchange of Gln291 to Asn in TM VI, almost full susceptibility to SMS 201-995 was obtained. Thus, it is concluded that the specificity of SMS 201-995 for SSTR2 is mainly defined by these two amino acids in transmembrane domains VI and VII. Using the conjugate gradient method we have, by analogy to the well established structure of bacteriorhodopsin, built a model for SRIF receptor-ligand interactions that explains the importance of Gln291 and Ser305 for the selectivity of agonists.

Amino Acid Sequence↗
PubMed1994

Localization of somatostatin (SRIF) SSTR-1, SSTR-2 and SSTR-3 receptor mRNA in rat brain by in situ hybridization.

In situ hybridization histochemistry was performed to analyse the distribution of the messenger RNA (mRNA) of three putative somatostatin (SRIF) receptors in rat brain, using oligonucleotide probes derived from the cDNA coding for SSTR-1, SSTR-2, and SSTR-3 receptors. SSTR-1 signals were found in layers V-VI of the cerebral cortex, in primary olfactory cortex, taenia tecta, subiculum, entorhinal cortex, granular layer of the dentate gyrus, amygdala and cerebellar nuclei. Signals for SSTR-2 were found in the frontal cerebral cortex (layers IV, V and VI), taenia tecta, claustrum, endopiriform nucleus, locus coeruleus, medial habenula, subiculum, granular cell layer of the dentate gyrus and amygdala. High levels of SSTR-3 hybridization were found in the olfactory bulb, primary olfactory cortex, islands of Calleja, medial habenula, amygdala, granular layer of the dentate gyrus, various thalamic and pontine nuclei and in the granular and Purkinje cell layers of the cerebellum. The distribution of the hybridization signals of the oligoprobes is consistent with the labelling of specific SRIF binding sites in rat brain. Especially, SSTR-2 and SSTR-1 oligos seem to label regions in which SS-1 and SS-2 receptors, respectively, have been previously characterized in autoradiographical studies. The situation is less clear with SSTR-3 mRNA, since SRIF binding in adult rats is usually low or absent in cerebellum, although some cerebellar nuclei appear to be labelled in the adult. The localization of SSTR-1, SSTR-2 and SSTR-3 mRNAs suggests that SRIF receptor subtypes in rat brain show profound differences in their distribution and are involved in a variety of central, in addition to neuroendocrine, functions.

Animals↗
PubMed1994

Exploring the mammalian neuromuscular system by analysis of mutations: spinal muscular atrophy and myotonia.

Any biological structure can be studied using mutations that interfere either with its emergence or its function. We investigate spontaneous and induced mutations in the mouse that affect neuromuscular development and function. The wobbler mouse (phenotype WR, genotype wr/wr) suffers from muscular atrophy because of the degeneration of 20-40% of the motoneurones; it is also unable to produce functional spermatozoa. As a step towards positional cloning of the wr gene, we have mapped the locus to proximal chromosome 11, thus excluding CNTF and its receptor as candidates, and suggesting the closely-linked Rab 1 gene encoding a GTP-binding protein as a possibility. In the case of the adr (arrested development of righting response) mouse, which shows hyperexcitability of mature muscle fibres due to a reduction of the 'dampening' function of chloride conductance at resting potential, we have shown that the defect is in the chloride channel gene adr/Clc-1 on chromosome 6. This allowed us to predict via synteny the chromosomal location of human Thomsen's and Becker's myotonias as close to the TCRB gene on human chromosome 7q. The combination of these approaches with gene-targeting approaches will allow genetic analysis of the establishment and structure of the neuromuscular system.

Animals↗
PubMed1993

Distribution and second messenger coupling of four somatostatin receptor subtypes expressed in brain.

The mRNA distribution in the brain and the coupling to cellular effector systems of four somatostatin receptors (SSTR1-4) was studied. All four SRIF receptor subtypes were expressed in cortex and hippocampus. In addition, SSTR1 mRNA was relatively abundant in the spinal cord whereas SSTR2 mRNA was also present in the striatum. The SSTR3 gene was predominantly expressed in the olfactory bulb and in the cerebellum. Conflicting results about the effector coupling of SSTR1-3 have been published previously. We have stably expressed human SSTR1-4 in HEK 293 human embryonal kidney cells. Agonist binding to the receptor subtypes, including the recently cloned SSTR4, inhibited the formation of forskolin-induced cAMP. Is is concluded that, in an appropriate cellular environment, all four receptor subtypes can functionally couple to the inhibition of adenylyl cyclase.

Base Sequence↗
PubMed1993

Cloning and characterization of the gene encoding murine insulin-like growth factor-binding protein-2, mIGFBP-2.

We present a characterization of the single-copy gene, mIGFBP-2, encoding the murine insulin-like growth factor-binding protein-2 (mIGFBP-2). It consists of four exons with sizes of 470 +/- 2, 227, 141 and > 475 nucleotides (nt). The first intron spans 23 kb of genomic sequence, and the complete gene extends to more than 28 kb. Two kb of the 5'-flanking region were sequenced. This region has no TATA or CAAT boxes but is G+G-rich and contains several potential regulatory sequence motifs. A total of five GC boxes, which may serve as potential binding sites for a transcription factor, Sp1, are present immediately upstream of the transcription start point (tsp). By primer extension, we identified a single tsp at nt position -85 +/- 2. The murine IGFBP-2 locus was mapped to the proximal region of mouse chromosome 1, to a region of conserved synteny with human chromosome 2q. A comparison of the deduced amino acid sequences of mouse, rat and human IGFBP-2 reveals a high degree of homology between all three species.

Animals↗
PubMed1993

Chromosomal localization and genomic cloning of the mouse alpha-tropomyosin gene Tpm-1.

In vertebrates, the alpha-tropomyosin gene, Tpm-1, codes for at least 9 tropomyosin isoforms that are expressed by tissue-specific alternative splicing. Using interspecies backcrosses, we have localized Tpm-1 on mouse chromosome 9, cen-Cyp1a2-Tpm-1-Mod-1-Mylc-Scn5a, near the d-se region. The restriction fragment length variant used for chromosomal assignment, as well as other restriction fragments hybridizing to a 3'-specific alpha-tropomyosin cDNA probe in genomic Southern blots, was investigated by cloning 17.5-kb of Tpm-1. The same restriction patterns were observed, proving the identity of the mapped and the cloned gene. The identity was supported by sequencing the 3' end of the gene.

Animals↗
PubMed1993

Chromosomal localization of the mouse titin gene and its relation to "muscular dystrophy with myositis" and nebulin genes on chromosome 2.

In the mouse, the genes for the structural components of the myofibril titin and nebulin, Ttn and Neb, map to proximal Chr 2, as does the gene for a muscle disease, "muscular dystrophy with myositis," mdm. To facilitate the evaluation of Ttn and Neb as possible candidates for mdm, we have determined their relative map positions, using a Mus spretus/Mus musculus interspecific backcross. The gene order (distances in cM) cenVim-16.9 +/- 4.7-Neb-7.6 +/- 3.0-Ttn, Acra-18.0 +/- 4.9-Pax-6-17.7 +/- 4.9-a ... has been determined. Considering the standard deviations, Neb, Ttn, and Acra could colocalize with mdm. Using Ttn and Neb probes, DNAs from mdm/mdm and mdm/+ mice were tested for restriction fragment variants in comparison to the M. musculus wildtype. No variants have been found with 11 restriction nucleases. Our data corroborate a conserved synteny comprising genes NEB, TTN, CHRNA1 on human Chr 2q.

Animals↗
PubMed1992

Wobbler, a mutation affecting motoneuron survival and gonadal functions in the mouse, maps to proximal chromosome 11.

The wobbler mouse (genotype wr/wr) has been considered as an animal model for human neurodegenerative disorders. In the homozygous condition, the autosomal mutation wobbler (wr) causes a motoneuron disease and gonadal dysfunction. We have genetically mapped the wr gene, using an interspecific backcross between the laboratory strain C57BL/6J (wr/+) and Mus spretus. The expected percentage of wobbler progeny were obtained, but heterogeneous expression of the wobbler phenotype indicated the existence of modifier genes in the M. spretus genetic background. The segregation of DNA markers of known chromosomal location among wobbler progeny and unaffected mice was scored. Close linkage of wr was obtained with Erbb and Rel on chromosome 11 and the gene order cen-Nfh-Erbb-wr-Rel-Hba-Il-3 was established. Closely linked markers like Erbb provide tools for a prognostic DNA diagnosis of the wobbler disease, and thereby for its analysis by descriptive and experimental embryology.

Animals↗
PubMed1992

The gene for the cell adhesion molecule M-cadherin maps to mouse chromosome 8 and human chromosome 16q24.1-qter and is near the E-cadherin (uvomorulin) locus in both species.

A mouse myotube-derived cDNA encoding the Ca(2+)-dependent cell adhesion molecule M-cadherin was used to study the segregation of the corresponding gene Cdh3 in a mouse interspecific backcross. Cdh3 was found to be unlinked to the N-cadherin gene but linked to the E-cadherin (uvomorulin) locus on chromosome 8 in a region of conserved synteny with human chromosome 16q. The gene order cen-Junb-Um-Tat-(Cdh3/Aprt) was determined. The human homologue CDH3 was mapped to chromosome 16q24.1-qter by analyzing human/mouse somatic cell hybrids.

Animals↗
PubMed1988

Dolichos biflorus agglutinin receptors in mouse muscle. I. Developmental expression in relation to synaptic acetylcholinesterase and to neuromuscular disease.

The lectin (agglutinin) from Dolichos biflorus (DBA) binds selectively to the neuromuscular junction of different vertebrate species. We have examined the synaptic DBA receptors in skeletal muscle during postnatal development and in neuromuscular diseases of the mouse. No DBA binding was found at neuromuscular junctions of muscles from newborn mice, when acetylcholine receptors and acetylcholinesterases were already concentrated at the endplate. Synaptic accumulation of DBA receptors was evident 4 days after birth, and the staining intensity increased until postnatal day 10 to 12 when it reached the adult level. As shown by ultrastructural histochemistry, accessible DBA binding sites were confined to the crests of junctional folds in motor endplates of 4-day-old mice, whereas adult endplates exhibited DBA binding sites in the entire synaptic cleft including the junctional folds. Two neuromuscular hereditary diseases of the mouse, 'wobbler' (WR) and 'motor endplate disease' (MED) were examined. At the light microscopic level, DBA binding was normal in WR and MED endplates. At the ultrastructural level, MED synapses showed reduced junctional folds but unaffected DBA binding capacity.

Acetylcholinesterase↗
PubMed1988

Dolichos biflorus agglutinin receptors in mouse muscle. II. Biochemical properties in relation to molecular forms of acetylcholinesterase.

A biochemical analysis has been performed on the relationship between the receptors for Dolichos biflorus agglutinin (DBA) and collagen tailed acetylcholinesterase (16S AChE) in mouse skeletal muscle. The molecular forms of AChE were separated by differential salt extraction and by gradient centrifugation. DBA binding activity was measured using a microtiter plate binding assay and affinity chromatography. The 16S form of AChE was bound to DBA, whereas globular forms of AChE were not. However, only a small proportion of 16S AChE was capable of binding to DBA, and most of the DBA binding capacity in muscle extracts was not associated with the 16S AChE. The possible association with the neuromuscular synapse of DBA binding molecules other than 16S AChE is discussed with respect to our previous histochemical study on DBA binding sites in mouse muscle.

Acetylcholinesterase↗