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H Geissler

Publications and source records attributed to H Geissler.

At least 19 recordsLinked to original sources
PubMed2000

Event-related brain potentials dissociate visual working memory processes under categorial and identical comparison conditions.

Event-related potentials (ERPs) have been successfully employed to examine the functional and neuronal characteristics of working memory processes. In the present study, we examined the ERP waveforms in a delayed matching task to examine the cognitive processes underlying category and identity comparison and the effects of stimulus complexity. Subjects had to decide whether two visual stimuli are (a) physically identical (identical comparison condition, IC) or (b) identical, irrespective of their orientation (categorial comparison condition, CC). The stimuli were structured five-point patterns, which varied in complexity. For the ERPs elicited during the 1500 ms retention interval, the following pattern of results was obtained: Stimuli in the CC-condition elicited larger P300 components than in the IC-condition. In the IC-condition, the P300 was followed by a broadly distributed negative slow wave. Moreover, complex patterns elicited a posteriorily distributed negativity at 350 ms (N350), whereas the less complex patterns gave rise to a fronto-centrally distributed slow wave that started around 500 ms. These results suggest that S1 was more elaborately processed in the CC-condition, while the more complex figures were associated with an early classification process during the retention interval.

Adult↗
PubMed2000

The tail domain of myosin M catalyses nucleotide exchange on Rac1 GTPases and can induce actin-driven surface protrusions.

Members of the myosin superfamily play crucial roles in cellular processes including management of the cortical cytoskeleton, organelle transport and signal transduction. GTPases of the Rho family act as key control elements in the reorganization of the actin cytoskeleton in response to growth factors, and other functions such as membrane trafficking, transcriptional regulation, growth control and development. Here, we describe a novel unconventional myosin from Dictyostelium discoideum, MyoM. Primary sequence analysis revealed that it has the appearance of a natural chimera between a myosin motor domain and a guanine nucleotide exchange factor (GEF) domain for Rho GTPases. The functionality of both domains was established. Binding of the motor domain to F-actin was ATP-dependent and potentially regulated by phosphorylation. The GEF domain displayed selective activity on Rac1-related GTPases. Overexpression, rather than absence of MyoM, affected the cell morphology and viability. Particularly in response to hypo-osmotic stress, cells overexpressing the MyoM tail domain extended massive actin-driven protrusions. The GEF was enriched at the tip of growing protuberances, probably through its pleckstrin homology domain. MyoM is the first unconventional myosin containing an active Rac-GEF domain, suggesting a role at the interface of Rac-mediated signal transduction and remodeling of the actin cytoskeleton.

Actins↗
PubMed1999

How many is enough? Exploring the myosin repertoire in the model eukaryote Dictyostelium discoideum.

The cytoplasm of eukaryotic cells is a very complex milieu and unraveling how its unique cytoarchitecture is achieved and maintained is a central theme in modern cell biology. It is crucial to understand how organelles and macro-complexes of RNA and/or proteins are transported to and/or maintained at their specific cellular locations. The importance of filamentous-actin-directed myosin-powered cargo transport was only recently realized, and after an initial explosion in the identification of new molecules, the field is now concentrating on their functional dissection. Direct connections of myosins to a variety of cellular tasks are now slowly emerging, such as in cytokinesis, phagocytosis, endocytosis, polarized secretion and exocytosis, axonal transport, etc. Unconventional myosins have been identified in a wide variety of organisms, making the presence of actin and myosins a hallmark of eukaryotism. The genome of S. cerevisiae encodes only five myosins, whereas a mammalian cell has the capacity to express between two and three dozen myosins. Why is it so crucial to arrive at this final census? The main questions that we would like to discuss are the following. How many distinct myosin-powered functions are carried out in a typical higher eukaryote? Or, in other words, what is the minimal set of myosins essential to accomplish the multitude of tasks related to motility and intracellular dynamics in a multicellular organism? And also, as a corollary, what is the degree of functional redundancy inside a given myosin class? In that respect, the choice of a model organism suitable for such an investigation is more crucial than ever. Here we argue that Dictyostelium discoideum is affirming its position as an ideal system of intermediate complexity to study myosin-powered trafficking and is or will soon become the second eukaryote for which complete knowledge of the whole repertoire of myosins is available.

Actins↗
PubMed1999

A potentially exhaustive screening strategy reveals two novel divergent myosins in Dictyostelium.

In recent years, the myosin superfamily has kept expanding at an explosive rate, but the understanding of their complex functions has been lagging. Therefore, Dictyostelium discoideum, a genetically and biochemically tractable eukaryotic amoeba, appears as a powerful model organism to investigate the involvement of the actomyosin cytoskeleton in a variety of cellular tasks. Because of the relatively high degree of functional redundancy, such studies would be greatly facilitated by the prior knowledge of the whole myosin repertoire in this organism. Here, we present a strategy based on PCR amplification using degenerate primers and followed by negative hybridization screening which led to the potentially exhaustive identification of members of the myosin family in D. discoideum. Two novel myosins were identified and their genetic loci mapped by hybridization to an ordered YAC library. Preliminary inspection of myoK and myoM sequences revealed that, despite carrying most of the hallmarks of myosin motors, both molecules harbor features surprisingly divergent from most known myosins.

Amino Acid Sequence↗
PubMed1998

Estimation of the growth rate of mixed ruminal bacteria from short-term DNA radiolabeling.

A method based on 32P-labeling of DNA in short-term incubations was developed for estimating the growth rate of mixed rumen bacteria. A freeze/thaw procedure was optimized to quantitatively disrupt mixed rumen bacteria and extract bacterial DNA. The preliminary enzymatic lysis step, with lysozyme rather than proteinase K, sodium lauroyl sarcosine, and, to a lesser extent, sodium dodecyl sulfate (SDS) strongly improved cell disruption and DNA recovery rates. Sodium deoxycholate, CHAPS or Triton X-100 had no significant effect. Increasing the number of cycles or lowering the freezing temperature from -20 degrees C to -50 degrees C had no effect on DNA extraction efficiency while setting the thawing temperature at +60 degrees C rather than +37 degrees C slightly increased DNA yield but also increased its contamination with RNA. The method finally selected led to the lysis of at least 93% of cells and to the extraction of 85% of bacterial DNA. The kinetics of in vitro 32P incorporation into rumen bacteria DNA was then determined in batch incubations of strained rumen contents with no additional substrate. The curvilinear effects of the amount of 32P and the incubation time (5-15 min) on the DNA radioactivity were investigated by applying a Doehlert experimental design and fitting a second order polynomial model to data. The DNA radioactivity was linearly related to time (p<0.02) with other coefficients in the model being equal to zero (p>0.20). The incorporation of 32P into bacterial DNA was initiated approximately 70 s after the start of incubation. Taking into account the accuracy of scintillation counting, 10-15 min incubations, with 15 microCi 32P and 10 mL rumen contents per tube, appeared satisfactory for future studies.

Journal Article↗
PubMed1997

Dictyostelium discoideum protein disulfide isomerase, an endoplasmic reticulum resident enzyme lacking a KDEL-type retrieval signal.

The primary activity of protein disulfide isomerase (PDI), a multifunctional resident of the endoplasmic reticulum (ER), is the isomerization of disulfide bridges during protein folding. We isolated a cDNA encoding Dictyostelium discoideum PDI (Dd-PDI). Phylogenetic analyses and basic biochemical properties indicate that it belongs to a subfamily called P5, many members of which differ from the classical PDIs in many respects. They lack an intervening inactive thioredoxin module, a C-terminal acidic domain involved in Ca2+ binding and a KDEL-type retrieval signal. Despite the absence of this motif, the ER is the steady-state location of Dd-PDI, suggesting the existence of an alternative retention mechanism for P5-related enzymes.

Amino Acid Sequence↗
PubMed1996

Cardiovascular Risk and Back-disorder Intervention Study of Mass Transit Operators.

A prospective intervention study was conducted to evaluate an employer/union-sponsored physical and psychological health program, which was offered to 125 transit operators aged >45 years with >15 years of job seniority. The one-year, biweekly program included physical exercise, relaxation, back school, and work-related stress management and diet counseling. A control group (n = 26) was available for comparison. Twenty-seven operators dropped out of the study. WHO cardiovascular risk survey methods, ergometry, Minnesota ECG coding, standardized low-back tests, blood lipids, lead, and carboxyhemoglobin were measured. Before the intervention, the ten-year cardiovascular-disease risk of all study subjects (15.1%) was greater than that of the general reference population (14.0%). After the intervention it fell to 12.9%, but not significantly compared with that of a non-exercising control group, which also showed a reduction. The prevalence and the self-rated intensity of back problems were reduced after the intervention: 55.4% of low-back-pain sufferers reported substantial improvement, and only 12.3% reported substantial worsening. The multidisciplinary intervention program appeared to be effective for musculoskeletal conditions, but not for overall cardiovascular risk, compared with the controls.

Journal Article↗
PubMed1995

Rab7 and Rab9 are recruited onto late endosomes by biochemically distinguishable processes.

Rab GTPases are localized to the surfaces of distinct membrane-bound organelles and function in transport vesicle docking and/or fusion. Prenylated Rab9, bound to GDP dissociation inhibitor-alpha, can be recruited selectively onto a membrane fraction enriched in late endosomes; this process is accompanied by nucleotide exchange. We used this system to address whether each Rab uses a distinct machinery to associate with its cognate organelle. Purified, prenylated Rab1B, Rab7, and Rab9 proteins were each reconstituted as stoichiometric complexes with purified GDP dissociation inhibitor-alpha, and their recruitment onto endosome- or ER-enriched membrane fractions was quantified. The two late endosomal proteins, Rab9 and Rab7, were each recruited onto endosome membranes with approximate apparent Km values of 9 and 22 nM, respectively. However, while control Rab9.GDP dissociation inhibitor-alpha complexes inhibited the initial rate of myc-tagged Rab9 recruitment with an apparent Ki of approximately 9 nM, Rab7 complexes inhibited this process much less effectively (apparent Ki approximately 112 nM). Similarly, complexes of the endoplasmic reticulum-localized Rab1B protein were even less potent than Rab7 complexes (apparent Ki approximately 405 nm). Rab9 complexes inhibited Rab7 recruitment with the same low efficacy as Rab7 complexes inhibited Rab9 recruitment. These experiments distinguish, biochemically, the recruitment of different Rab proteins onto a single class of organelle. Since Rab7 and Rab9 are both localized at least in large part, to late endosomes, this suggests that a single organelle may bear multiple Rab recruitment machines.

Animals↗
PubMed1991

Effect time-course of the inhibition of histamine induced skin reactions by orally applied dimethindene maleate.

We have investigated the time-course of the flare inhibiting activity of dimethindene maleate in man and compared the resulting effect-kinetic data with those from pharmacokinetic investigations. The study was carried out in a double-blind, placebo-controlled cross-over design with randomly assigned healthy volunteers. Dimethindene maleate (4 mg) was orally applied, followed by intracutaneous histamine provocations (-1, 2, 5, 14, 17, 20, 23, 26, 29 h). The two cross-over periods were separated by a wash-out phase of 17 h. Flare areas were documented 5, 10, 20 and 30 min after provocation with histamine. A strong inhibition of the development of flares was observed. With regard to the time-course of the inhibiting effect, its maximum was observed at a provocation time of 5 h. The mean residence time of the inhibiting effect was calculated to be ca. 13 h. This is different from the mean residence time of ca. 8 h obtained from blood level data. Blood- and effect-levels are not linearly related under oral treatment conditions.

Adult↗
PubMed1990

Time course of the effect of intravenous dimetindene maleate.

In order to evaluate the time course of its effects, dimetindene maleate has been investigated in a histamine provocation model in man. Eight healthy male volunteers were treated i.v. with 4 mg dimetindene maleate or sodium chloride solution in a double blind, cross over study. Intracutaneous histamine injections were given at -1, 2, 5, 14, 17, 20, 23, 26, and 29 h following drug administration and the areas of flares and wheals were measured after 5, 10, 20, and 30 min. There was strong inhibition of the development both of flares and wheals, which was more pronounced for the former. Baseline adjusted areas under the curve differed significantly following drug and placebo treatment. The maximum effect was observed at 2 h. The mean residence time of the inhibitory effect was calculated to be approximately 13 h compared to the mean residence time of dimetindene in blood of approximately 5 h, which indicates a non-linear relationship between blood level and effect.

Adult↗
PubMed1990

Effect-time-relation of the H1-receptor antagonist dimethindene maleate following intravenous injection.

We have investigated the time-course of the weal and flare inhibiting activity of dimethindene maleate in man and compared the resulting effect-kinetic data with those from pharmacokinetic investigations. The study was carried out in a double blind, placebo controlled cross-over design with randomly assigned healthy volunteers. Dimethindene maleate (4 mg) was intravenously injected, followed by intracutaneous histamine provocations (-1, 2, 5, 14, 17, 20, 23, 26, and 29 h). The two cross-over periods were separated by a wash-out phase of 17 h. Flare and weal areas were documented 5, 10, 20, and 30 min after provocation with histamine. A strong inhibition of the development of flares and weals was observed and was more pronounced in flares than in weals. With regard to the time course of the inhibiting effect, its maxima both for flares and weals were observed at a provocation time of 2 h. The mean residence time of the inhibiting effect was calculated to be ca. 13 h for flares and ca. 15 h for weals. These values are nearly 2-3 times as high as the mean residence time of 6 h calculated from blood level data. Blood- and effect-levels are thus non-linearly related.

Adult↗
PubMed1990

Effect-kinetic characterization of dimethindene maleate following oral administration (Fenistil, Tropfen).

Dimethindene maleate is a well known H1-receptor antagonist with strong affinity to the H1-receptor. In order to evaluate the time course of its activity, dimethindene maleate was investigated in a histamine provocation model in man. Eight healthy male volunteers were treated either with 4 mg dimethindene maleate using a commercially available solution (Fenistile, Tropfen) or an identically appearing placebo solution (po) following a double-blind, crossover study design. Intracutaneous histamine injections were administered at -1, 2, 5, 14, 17, 20, 23, 26 and 29 h following drug administration. Areas of flares and weals were measured 5, 10, 20, and 30 min following histamine provocation. A strong inhibition of the development of flares and weals was observed to be more pronounced in flares than in weals. Baseline adjusted areas under the curve differ statistically significantly following verum and placebo treatment conditions (P = 0.0028). According to the time schedule of the study maximal effects were observed at time point 5 h. The mean residence times of the inhibitory effects were calculated to be congruent to 13 h compared to the mean residence times of dimethindene blood levels of approximately 8 h indicating a non-linear relationship between blood level and effect.

Administration, Oral↗
PubMed1990

Variations of skin sensitivity to intracutaneous histamine provocations with regard to provocation time.

Dermal provocation tests with histamine and other mediators of allergy are widely used as diagnostic tools and as clinical pharmacological models. Diurnal variations of skin reactivity e.g. flare reactions have been postulated earlier. Potential differences in skin reactivity using histamine provoked flare areas as model were investigated by means of five different placebo formulations (i.v. solution; p.o. solution; p.o. solid forms). Flare reactions have been provoked every 3rd hour within a time span of 29 h using a cross-over design with an H1-antagonist positive control. No provocation was provided between 0:00 and 7:00 a.m. There was no statistically significant variation of skin reactivity with respect to provocation times under placebo treatment conditions. No dependence on plasmacortisol levels was observed. Interindividual differences in skin reactivity are more pronounced than the intraindividual variations.

Adult↗