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G Reuter

Publications and source records attributed to G Reuter.

At least 19 recordsLinked to original sources
PubMed1997

Mammalian homologues of the Polycomb-group gene Enhancer of zeste mediate gene silencing in Drosophila heterochromatin and at S. cerevisiae telomeres.

Gene silencing is required to stably maintain distinct patterns of gene expression during eukaryotic development and has been correlated with the induction of chromatin domains that restrict gene activity. We describe the isolation of human (EZH2) and mouse (Ezh1) homologues of the Drosophila Polycomb-group (Pc-G) gene Enhancer of zeste [E(z)], a crucial regulator of homeotic gene expression implicated in the assembly of repressive protein complexes in chromatin. Mammalian homologues of E(z) are encoded by two distinct loci in mouse and man, and the two murine Ezh genes display complementary expression profiles during mouse development. The E(z) gene family reveals a striking functional conservation in mediating gene repression in eukaryotic chromatin: extra gene copies of human EZH2 or Drosophila E(z) in transgenic flies enhance position effect variegation of the heterochromatin-associated white gene, and expression of either human EZH2 or murine Ezh1 restores gene repression in Saccharomyces cerevisiae mutants that are impaired in telomeric silencing. Together, these data provide a functional link between Pc-G-dependent gene repression and inactive chromatin domains, and indicate that silencing mechanism(s) may be broadly conserved in eukaryotes.

Amino Acid Sequence↗
PubMed1997

Both invariant chain isoforms Ii31 and Ii41 promote class II antigen presentation.

The invariant chain (Ii) gene encodes two differentially spliced variants Ii31 and Ii41. The Ii31 isotype is the dominant form expressed in all antigen-presenting cells (APC). Ii41 is differentially expressed and can be found in large quantities in Langerhans and dendritic cells. While a functional role of Ii in class II antigen presentation is now well established, a distinct role of the Ii isotypes remains controversial. We tested Ii31 and Ii41 L cell transfectants for antigen presentation of hen egg lysozyme (HEL) to T cell hybridomas. The result indicates that both Ii chains promote antigen presentation equally well. To test other APC than transfected L cells, we introduced a recombinant Ii41 gene into anti-deficient mouse line. There the transgene induces about one-third of total li expression of wild-type mice. Surface expression of class II molecules and the CD4 compartment which are deficient in Ii knock-out mice are restored in Ii41 transgenic mice. B lymphocytes from Ii41 transgenic mice and Ii31-expressing B lymphocytes from wild-type mice were used as APC for presentation of keyhole limpet hemacyanin and ovalbumin to T cell hybridomas. The results show that both Ii chains facilitate antigen presentation equally well.

Animals↗
PubMed1997

Optical imaging of cat auditory cortex cochleotopic selectivity evoked by acute electrical stimulation of a multi-channel cochlear implant.

We measured reflectance changes by means of optical imaging of intrinsic signals to study the effects of acute electrical cochlear stimulation on the topography of the cat auditory cortex. After single-pulse electrical stimulation at selected sites of a multichannel implant device, we found topographically restricted response areas representing mainly the high-frequency range in AI. Systematic variation of the stimulation pairs and thus of the cochlear frequency sites revealed a systematic and corresponding shift of the response areas that matched the underlying frequency organization. Intensity functions were usually very steep. Increasingly higher stimulation currents evoked increasingly larger response areas, resulting in decreasing spatial, i.e. cochleotopic, selectivity; however, we observed only slight positional shifts of the focal zones of activity. Electrophysiological recordings of local field potential maps in the same individual animals revealed close correspondence of the locations of the cortical response areas. The results suggest that the method of optical imaging can be used to map response areas evoked by electrical cochlear stimulation, thereby maintaining a profound cochleotopic selectivity. Further experiments in chronically stimulated animals will shed more light on the degree of functional and reorganizational capacities of the primary cortex and could be beneficial for our understanding of the treatment of profound deafness.

Animals↗
PubMed1996

The histone deacetylase RPD3 counteracts genomic silencing in Drosophila and yeast.

Both position-effect variegation (PEV) in Drosophila and telomeric position-effect in yeast (TPE) result from the mosaic inactivation of genes relocated next to a block of centromeric heterochromatin or next to telomeres. In many aspects, these phenomena are analogous to other epigenetic silencing mechanisms, such as the control of homeotic gene clusters, X-chromosome inactivation and imprinting in mammals, and mating-type control in yeast. Dominant mutations that suppress or enhance PEV are thought to encode either chromatin proteins or factors that directly affect chromatin structure. We have identified an insertional mutation in Drosophila that enhances PEV and reduces transcription of the gene in the eye-antenna imaginal disc. The gene corresponds to that encoding the transcriptional regulator RPD3 in yeast, and to a human histone deacetylase. In yeast, RRD3-deletion strains show enhanced TPE, suggesting a conserved role of the histone deacetylase RPD3 in counteracting genomic silencing. This function of RPD3, which is in contrast to the general correlation between histone acetylation and increased transcription, might be due to a specialized chromatin structure at silenced loci.

Amino Acid Sequence↗
PubMed1996

Binding specificity of influenza C-virus to variably O-acetylated glycoconjugates and its use for histochemical detection of N-acetyl-9-O-acetylneuraminic acid in mammalian tissues.

The specificity of influenza C-virus binding to sialoglycoconjugates was tested with various naturally O-acetylated gangliosides or synthetically O-acetylated sialic acid thioketosides, which revealed binding to 9-O-acetylated N-acetylneuraminic acid. Binding was also observed with a sample of Neu5,7Ac2-GD3, however at a lower degree. Sialic acids with two or three O-acetyl groups in the side chain of synthetic sialic acid derivatives are not recognized by the virus. In these experiments, bound viruses were detected with esterase substrates. Influenza C-virus was also used for the histological identification of mono-O-acetylated sialic acids in combination with an immunological visualization of the virus bound to thin-sections. The occurrence of these sialic acids was demonstrated in bovine submandibular gland, rat liver, human normal adult and fetal colon and diseased colon, as well as in human sweat gland. Submandibular gland and colon also contain significant amounts of glycoconjugates with two or three acetyl esters in the sialic acid side chain, demonstrating the value of the virus in discriminating between mono- and higher O-acetylation at the same site. The patterns of staining showed differences between healthy persons and patients with colon carcinoma, ulcerative colitis or Crohn's disease. Remarkably, some human colon samples did not show O-acetyl sialic acid-specific staining. The histochemical observations were controlled by chemical analysis of tissue sialic acids.

Acetylation↗
PubMed1996

Molecular dynamics-derived conformation and intramolecular interaction analysis of the N-acetyl-9-O-acetylneuraminic acid-containing ganglioside GD1a and NMR-based analysis of its binding to a human polyclonal immunoglobulin G fraction with selectivity for O-acetylated sialic acids.

The influence of 9-O-acetylation of GD1a, yielding GD1a (eNeu5,9Ac2) with a 9-O-acetylated sialic acid moiety linked to the outer galactose residue, on the spatial extension and mobility of the carbohydrate chain and on recognition by a natural human antibody is analysed. To study a potential impact of the O-acetyl group on the overall conformation of the carbohydrate chain, molecular dynamics (MD) simulations of oligosaccharide chain fragments of increasing length starting from the non-reducing end have been carried out for the first time in this study. They revealed a considerable loss in chain flexibility after addition of the internal N-acetylneuraminic acid onto the chain. Besides MD calculations with different dielectric constants, the conformational behaviour of the complete oligosaccharide chain of the 9-O-acetylated GD1a ganglioside was simulated in the solvents water and dimethyl sulfoxide. These solvents were also used in NMR measurements. The results of this study indicate that 9-O-acetylation at the terminal sialic acid does not influence the overall conformation of the ganglioside. An extended interaction analysis of energetically minimized conformations of GD1a (eNeu5,9Ac2) and GD1a, obtained during molecular dynamics simulations, allowed assessment of the influence of the different parts of the saccharide chains on spatial flexibility. Noteworthy energetic interactions, most interestingly between the 9-O-acetyl group and the pyranose ring of N-acetylgalactosamine, were ascertained by the calculations. However, the strength of this interaction does not force the ganglioside into a conformation, where the 9-O-acetyl group is no longer accessible. Binding of GD1a (eNeu5,9Ac2) to proteins, which are specific for 9-O-acetylated sialic acids, should thus at least partially be mediated by the presence of this group. To experimentally prove this assumption, a NMR study of 9-O-acetylated GD1a in the presence of an affinity-purified polyclonal IgG fraction from human serum with preferential binding to 9-O-acetylated sialic acid was performed. The almost complete disappearance of the intensity of the 9-O-acetyl methyl signal of the GD1a (eNeu5,9Ac2) clearly indicates that the assumed interaction of the 9-O-acetyl group with the human protein takes place.

Acetylation↗
PubMed1996

Lactobacillus curvatus subsp. curvatus subsp. nov. and Lactobacillus curvatus subsp. melibiosus subsp. nov. and Lactobacillus sake subsp. sake subsp. nov. and Lactobacillus sake subsp. carnosus subsp. nov., new subspecies of Lactobacillus curvatus Abo-Elnaga and Kandler 1965 and Lactobacillus sake Katagiri, Kitahara, and Fukami 1934 (Klein et al. 1996, emended descriptions), respectively.

Lactobacillus curvatus and Lactobacillus sake are each genetically homogeneous species, as indicated by the high levels of DNA homology (> or = 76%) exhibited by strains of these taxa. However, the results of a numerical analysis of total soluble cell protein patterns and biochemical test data revealed that there are two phenotypic subgroups within L, curvatus and two phenotypic subgroups within L. sake. The overall randomly amplified polymorphic DNA (RAPD)-PCR band patterns obtained for the majority of L. curvatus strains corresponded well to the pattern obtained for the type strain of L. curvatus (strain DSM 20019). However, six strains of L. curvatus had different, but similar, RAPD-PCR profiles and grouped in a separate genetic cluster, which was linked to one of the clusters of L. sake strains. On the basis of these results, differences in biochemical and physiological characteristics, and total soluble cell protein profiles, we describe the subspecies L. curvatus subsp. curvatus subsp. nov. and L. curvatus subsp. melibiosus subsp. nov. for L. curvatus Abo-Elnaga and Kandler 1965 (Klein et al. 1996, emended description). Strains of L. sake grouped in two RAPD-PCR clusters, which was consistent with previous reports of phenotypic heterogeneity. Strains of Lactobacillus bavaricus, including type strain LMG 9844, clustered with the type strain of L. sake (strain NCFB 2714), indicating that these organisms belong to the same genetic group. We propose that strains of L. sake Katagiri, Kitahara, and Fukami 1934 (Klein et al. 1996, emended description) should be reclassified as members of L. sake subsp. sake subsp. nov. and L. sake subsp. carnosus subsp. nov. Strains of L. bavaricus are reclassified as members of L. sake subsp. sake, and the name L. bavaricus Stetter and Stetter 1980 is rejected.

DNA, Bacterial↗
PubMed1996

Position-effect variegation in Drosophila depends on dose of the gene encoding the E2F transcriptional activator and cell cycle regulator.

A dominant mutation due to the insertion of a P-element at 93E on the third chromosome of Drosophila melanogaster enhances position-effect variegation. The corresponding gene was cloned by transposon tagging and the sequence of the transcript revealed that it corresponds to the gene encoding the transcriptional activator and cell cycle regulator dE2F. The transposon-tagged allele is homozygous viable, and the insertion of the transposon in an intron correlates with a strong reduction in the amount of transcript. A homozygous lethal null allele was found to behave as a strong enhancer when heterozygous. Overexpression of the gene in transgenic flies has the opposite effect of suppressing variegation. A link is established here, and discussed, between the dose of a transcriptional activator, which controls the cell cycle, and epigenetic silencing of chromosomal domains in Drosophila.

Amino Acid Sequence↗
PubMed1996

Sialic acids structure-analysis-metabolism-occurrence-recognition.

Sialic acids are commonly positioned at non-reducing termini of complex carbohydrates. Steady refinements of analytical techniques have enabled detailed mapping of the complexity of sialic acids, unravelling a number of possibilities for substitutions. These developments have aided the description of the required enzymatic activities. In view of the physiological significance of this intriguing extent of variability of one sugar unit, the assumption that distinct types of sialic acids can serve as ligands in recognitive interactions is gaining support. It is reinforced by the discovery of several classes of mammalian lectins that bind sialo-glycoconjugates. Notably, an often encountered modification of sialic acids, namely O-acetylation, can be considered as a modulatory signal in recognition, either serving as contact point or masking a ligand structure. The increased knowledge of the physiological roles of sialic acids, for example in selectin-mediated leukocyte recruitment to sites of inflammation or in influenza virus propagation, even points to clinical applications. This perspective has led the field from the inherently descriptive beginning to technically sophisticated attempts for deliberate drug design.

Animals↗
PubMed1995

Effect of enzymatic desialylation of human serum amyloid P component on surface exposure of laser photo CIDNP (chemically induced dynamic nuclear polarization)--reactive histidine, tryptophan and tyrosine residues.

The human pentraxin serum amyloid P component (SAP) exhibits no microheterogeneity in its complex di-antennary glycan. To elucidate whether the removal of sialic acids from this glycoprotein might affect the accessibility of certain amino acid residues of the protein we employed the laser photo CIDNP approach as a sensitive tool. The CIDNP effect is created by the interaction of a photoexcited dye with reactive amino acids and results in enhanced absorption- or emission-signals which can be observed for the three aromatic amino acids histidine, tryptophan, and tyrosine if they are accessible to the dye. Therefore, this technique can be applied to explore surface exposure of these residues. The respective spectra of SAP and enzymatically desialylated SAP were determined. Six tryptophan/histidine signals and one tyrosine signal are present in the aromatic part of the CIDNP difference spectrum of SAP. The corresponding spectrum of desialylated SAP shows remarkable alterations. The chemical shift of one tryptophan/histidine-characteristic signal is decreased by 0.1 ppm. One tryptophan/histidine signal disappeared and a new one was formed in the CIDNP difference spectrum of desialylated SAP, while the other signals were unaffected. The tyrosine signal has a clearly enhanced intensity in desialylated SAP. Therefore, the removal of sialic acid moieties from the single N-glycan of each monomer apparently affects surface presentation of distinct CIDNP-reactive amino acids of SAP.

Amino Acids↗
PubMed1995

A threshold decrease for electrically stimulated motor responses of isolated aging outer hair cells from the pigmented guinea pig.

When outer hair cells are isolated from guinea pig cochleas and are placed in normal Hank's medium, they exhibit aging as a slow tonic reduction in length and increase in diameter. During this time the lateral subsurface cisternae become progressively vesiculated and the optical density of the border seen under phase-contrast microscopy decreases. A study of 65 outer hair cells was carried out using video imaging of this process. The base of each cell bonded to the Petri dish and the motility of the cuticular plate was recorded in two ways. To quantify the slow contraction of each preparation, the dimensions of the cell were measured from video replay. Displacements of the cuticular plate in response to an alternating electric field in line with the cell axis were also monitored using a video tracking technique. The amplitude of a 1 Hz stimulus required to cause a visually detectable motor response above baseline noise decreased as the cell degraded. Typically, fresh cylindrical cells exhibiting high optical contrast showed relatively small movements for field strengths up to 2 kVm-1. However, as the cell depolarized, the rigidity initially decreased and the cell could respond to field strengths down to 0.1 kVm-1 before cell death ultimately occurred. Such a threshold phenomenon in the isolated OHC has not been demonstrated directly until now. This result explains the variability of electromotility in aging in vitro preparations from the cochlea.

Animals↗
PubMed1995

Intra-species characterization of clinical isolates and biotechnologically used strains of Lactobacillus rhamnosus by analysis of the total soluble cytoplasmatic proteins with silver staining.

Lactobacillus rhamnosus is often used in milk products because of its technological properties, however it is supposed to be related to human infections as well. Therefore, 23 L. rhamnosus strains, including the type strain, were investigated. Nine strains resulted from biotechnological sources, 14 isolates had a clinical background, 13 came from a swedish culture collection. Biochemical and physiological properties were proved by classical tests. Analysis of the total soluble cytoplasmatic protein patterns was performed with diamine silver staining, a technique not previously applied to lactobacilli. Classical tests were able to confirm all strains as L. rhamnosus. Analysis of protein patterns allowed to differentiate between three clusters. Cluster I contained the type strain and biotechnologically used strains and one clinical strain isolated in Berlin. The second consisted of both, technological and clinical strains. The third cluster contained clinical isolates alone. SDS-PAGE of proteins together with diamine silver staining seems to be helpful to detect intra-species differences. It was stated, that technologically used strains of L. rhamnosus could clearly be differentiated from each other and also from clinical isolates.

Bacterial Proteins↗
PubMed1995

Sound-induced displacement responses in the plane of the organ of Corti in the isolated guinea-pig cochlea.

Sound-induced displacement responses in the plane of the organ of Corti were studied in the apical turn in the isolated temporal-bone preparation of the guinea-pig cochlea. Swept sinusoidal sound stimuli (100-500 Hz) were delivered closed-field to the external auditory meatus. The surface of the organ of Corti was continuously monitored using a CCD video camera. Displacement responses in the plane of the organ of Corti were determined by analyzing the change of the location of the cells (pixel-by-pixel) within the visual field of the microscope. Displacement responses followed the stimulus amplitude and were observable at Hensen's cells, three rows of outer hair cells and inner hair cells. The most prominent displacement responses were over the outer hair cells; the maximum amplitude was 0.6-1.7 microns at 100 dB SPL. Tuned displacement responses were found; the Q10 dB was 1.3 +/- 0.6. The best frequency was tonotopically organized, decreasing toward the apex with a space constant of 0.4-0.9 mm/oct. The motion was directed either strial-apically or strial-basally in a frequency dependent manner. With the aid of laser interferometric measurements of the transverse displacement, it was concluded that sound stimulation does not induce slow DC motion in the organ of Corti for the isolated temporal-bone preparation.

Acoustic Stimulation↗
PubMed1994

The Trithorax-like gene encodes the Drosophila GAGA factor.

Little is known about the way higher-order chromatin structure influences gene expression and chromosome topology in general. Genetic analysis in Drosophila has led to the discovery of two classes of genes, the regulators of homeotic genes and the modifiers of position-effect variegation, which seem to be good candidates for encoding some of the factors regulating chromatin functions. The Trithorax-like gene we described here is required for the normal expression of the homeotic genes and is a modifier of position-effect variegation. We found that Trithorax-like encodes the GAGA factor which is involved in the formation of an accessible chromatin structure at promoter sequences. Our genetic analysis suggests that the chromatin modelling function of the GAGA factor is not restricted to promoter regions.

Animals↗
PubMed1994

The protein encoded by the Drosophila position-effect variegation suppressor gene Su(var)3-9 combines domains of antagonistic regulators of homeotic gene complexes.

Modifier mutations of position-effect variegation (PEV) represent a useful tool for a genetic and molecular dissection of genes connected with chromatin regulation in Drosophila. The Su(var)3-9 gene belongs to the group of haplo suppressor loci which manifest a triplo enhancer effect. Mutations show a strong suppressor effect even in the presence of PEV enhancer mutations, indicating a central role of this gene in the regulation of PEV. By molecular analysis, Su(var)3-9 could be correlated with a 2.4 kb transcript which encodes a putative protein of 635 amino acids containing a chromo domain and a region of homology to Enhancer of zeste and trithorax, two antagonistic regulators of the Antennapedia and Bithorax gene complexes, as well as to the human protein ALL-1/Hrx which is implicated in acute leukemias. This region of homology is found in all four proteins at the C-terminus. The homology of Su(var)3-9 to both negative (Polycomb and Enhancer of zeste) and positive (trithorax) regulators of the Antennapedia and Bithorax complexes also suggests similarities in the molecular processes connected with stable transmission of a determined state and the clonal propagation of heterochromatinization.

Amino Acid Sequence↗
PubMed1994

Acute gentamicin ototoxicity in cochlear outer hair cells of the guinea pig.

The acute effects of the aminoglycoside antibiotics gentamicin on isolated cochlear outer hair cells (OHC) was investigated by whole-cell patch-clamp and measurements of the intracellular potassium level by means of the potassium-sensitive dye PBFI. In addition, the accompanying length changes of OHC are described. It could be shown that gentamicin at different concentrations reversibly induces a hyperpolarization by about 5-10 mV, potassium outflow from the cytoplasm (by about 22 mM) and a cellular elongation (by about 10%). It is suggested that these effects are the result of an interaction between gentamicin and the cochlear transduction channels in OHC as suggested earlier. These acute effects are distinctly different from the chronic gentamicin effects which are based on the metabolization of the antibiotics to cause the death of the OHC by interaction with the phosphoinositide signalling cascade.

Animals↗
PubMed1994

Transitory endolymph leakage induced hearing loss and tinnitus: depolarization, biphasic shortening and loss of electromotility of outer hair cells.

There are types of deafness and tinnitus in which ruptures or massive changes in the ionic permeability of the membranes lining the endolymphatic space [e.g., of the reticular lamina (RL)] are believed to allow potassium-rich endolymph to deluge the low [K+] perilymphatic fluid (e.g., in the small spaces of Nuel). This would result in a K+ intoxication of sensory and neural structures. Acute attacks of Ménière's disease have been suggested to be an important example for this event. The present study investigated the effects of transiently elevated [K+] due to the addition of artificial endolymph to the basolateral cell surface of outer hair cells (OHC) in replicating endolymph-induced K+ intoxication of the perilymph in the small spaces of Nuel. The influence of K+ intoxication of the basolateral OHC cell surface on the transduction was then examined. Intoxication resulted in an inhibition of the physiological repolarizing K+ efflux from hair cells. This induced unwanted depolarizations of the hair cells, interfering with mechanoelectrical transduction. A pathological longitudinal OHC shortening was also found, with subsequent compression of the organ of Corti possibly influencing the micromechanics of the mechanically active OHC. Both micromechanical and electrophysiological alterations are proposed to contribute to endolymph leakage induced attacks of deafness and possibly also to tinnitus. Moreover, repeated or long-lasting K+ intoxications of OHC resulted in a chronic and complete loss of OHC motility. This is suggested to be a pathophysiological basis in some patients with chronic hearing loss resulting from Ménière's syndrome.

Action Potentials↗