Structure and function of the betaine uptake system BetP of Corynebacterium glutamicum: strategies to sense osmotic and chill stress

The soil bacterium Corynebacterium glutamicum has to cope with frequent fluctuations of the external osmolarity and temperature. The consequences of hyperosmotic and chill stress seem to differ, either causing dehydration of the cytoplasm or leading to impairment of cellular functions due to low temperature. Nevertheless, a particular type of regulatory response, namely the accumulation of so-called compatible solutes, is induced under both conditions. Compatible solutes are known to stabilize the native conformation of enzymes, which may be affected by osmotic and chill stress. BetP is a high-affinity uptake carrier for the compatible solute glycine betaine in C. glutamicum. BetP includes, besides its catalytic function, the ability to sense hyperosmotic conditions and chill stress. As a consequence, the carrier is activated in dependence of the extent of these types of stress. The signal input related to these changes of the environmental conditions is based on at least two different mechanisms. In case of hyperosmotic stress, BetP responds to the internal potassium concentration as a measure for hypertonicity, whereas chill stress is detected by an independent signal, most probably changes of the physical state of the membrane.     

Resection of small plexiform neurofibromas in neurofibromatosis type 1 children

BACKGROUND: Plexiform neurofibromas (PNF) are benign tumors of the peripheral nerve which mostly develop in patients with neurofibromatosis type 1 (NF1). Surgical interventions are usually not applied to children with small tumors. These are rather restricted to debulking of larger tumors in adults that cause clinical complications or aesthetic disfigurement. In most cases, a total resection of PNF is not possible due to the network-like growth of the tumors. PATIENTS AND METHODS: Early surgical intervention was carried out for 9 small PNFs in 7 NF1 children. Tumor resection was performed following the graphical delineation of the affected skin and according the MRI findings. RESULTS: Total resection was achieved for all 9 PNF without causing any neurological or organic deficit. Annual magnetic resonance tomography over a period of four years did not reveal any relapse of the tumors. CONCLUSIONS: Early surgical intervention for small superficial PNFs in NF1 children have various advantages and may especially be considered a strategy to prevent progression.     

A putative high affinity hexose transporter, hxtA, of Aspergillus nidulans is induced in vegetative hyphae upon starvation and in ascogenous hyphae during cleistothecium formation

Fungi employ different carbohydrate uptake systems to adapt to certain environmental conditions and to different carbon source concentrations. The hydrolysis of polymeric carbohydrates and the subsequent uptake of monomeric forms may also play a role in development. Aspergillus nidulans accumulates cell wall components during vegetative growth and degrades them during sexual development. We have identified the hxtA (high affinity hexose transporter) gene in a differential library, which was enriched for sexual-specific genes. The hxtA gene is disrupted by 6 introns and predicted to encode a 531 amino acid protein with high similarity to major facilitator superfamily members including the high affinity hexose transporter Gtt1 from Trichoderma harzianum. A. nidulans HxtA contains the 12 predicted transmembrane domains characteristic for this family. Deletion of hxtA did not impair growth of A. nidulans on a variety of carbon sources nor did it inhibit sexual development suggesting redundant sugar uptake systems. We found at least 17 putative hexose transporters in the genome of A. nidulans. Despite the high similarity of HxtA to fungal high affinity glucose transporters, the hxtA gene did not restore growth on glucose of a Saccharomyces cerevisiae mutant, in which all hexose transporters were deleted. Northern blot analysis revealed that the A. nidulans hxtA gene was repressed under high glucose conditions and expressed in vegetative hyphae upon carbon starvation and during sexual development. We found hxtA(p)::sgfp expression in developing cleistothecia specifically in ascogenous hyphae and propose that HxtA is a high affinity glucose transporter involved in sugar metabolism during sexual development.     

Nuclear migration and positioning in filamentous fungi

Genetic analyses of nuclear distribution mutants have indicated that functions of the microtubule motor, cytoplasmic dynein, and its regulators are important for nuclear positioning in filamentous fungi. Here we review these studies and also present the need to further dissect how dynein and its associated microtubule cytoskeleton are involved mechanistically in nuclear positioning in the multinucleated hyphae.     

Distance-related semi-quantitative estimation of the extramatrical ectomycorrhizal mycelia of <Emphasis Type="Italic">Cortinarius obtusus</Emphasis> and <Emphasis Type="Italic">Tylospora asterophora</Emphasis>

Extramatrical mycelia of ectomycorrhizae (ECM) can markedly differ in their density, organization and extension as well as in their biomass. As these mycelia are very important for nutrient uptake, are sinks for carbohydrates and probably act as potential agents to interfere with mycelia of other ECM, a method allowing calculations of density, extension and amount of extramatrical mycelium could further ecological studies at different scales. As a first step synthesized ECM of Cortinarius obtusus and Tylospora asterophora, which represent two different ‘exploration types’ — T. asterophora belongs to the 'short distance exploration type’ and C. obtusus to the ‘medium distance exploration fringe subtype’ — were compared with respect to their extramatrical mycelia. To investigate the mycelial distribution in detail, flat rhizotrons filled with peat were used to synthesize the ECM on roots of Picea abies (Norway spruce). As both species form white mycelia, they contrast conspicuously to the dark brown peat substrate. This made it favourable to use CD-camera photographs and a consecutive image analysis of the bright mycelium in comparison to the dark background. For that, nine distance areas have been defined as the regions between nine concentric lines placed around the mantle surface of the ectomycorrhizal root (EMR). The distances between these lines were fixed in a regular manner as the square multiples of roughly one diameter of the EMR (0,27 mm). This resulted in lines representing distances of 1, 4, 9, 16, 25, 36, 49, 64, and 81 multiples of the EMR diameter. The distance of 81 EMR diameters equals roughly a real distance of app. 20 mm from the surface of the EMR. The studies showed highly significant differences in mycelial density between the four innermost distance areas, i. e. areas up to a distance of 16 EMR diameters. This applied for both species. Significant differences were found in the same areas when both species were compared. It was shown that C. obtusus still forms a considerable amount of mycelium beyond the 49 distance line, where the substrate was covered by 15–20 %. However, a limited data set did not allow any statistical calculations at these positions. In contrast to C. obtusus, the amount of extramatrical mycelium of T. asterophora decreased more rapidly with increasing distance. Mycelium could not be detected with this method beyond the 49 distance line. We conclude that these two species differ considerably in the amount and extension of their mycelia and this may be in line with their assignment to the respective exploration types. Further studies are needed to substantiate these results with additional species representing the full set of known exploration types. Envisaged correlation studies of these results with mycelial biomass by direct measurement of hyphal length or via quantitative PCR, can possibly result in an estimation of extramatrical mycelia of ECM in natural soil.     

Effects of natural and chemically synthesized furanones on quorum sensing in <Emphasis Type="Italic">Chromobacterium violaceum</Emphasis>

Background  

Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions:     

The Drosophila hugin gene codes for myostimulatory and ecdysis-modifying neuropeptides

In a genomic screen we isolated the Drosophila gene hugin (hug, cytology 87C1-2) by cross-hybridisation to a human glial cell line-derived neurotrophic factor cDNA. Upon cDNA sequence analysis and in vitro expression assays, the hugin gene was found to encode a signal peptide containing proprotein that was further processed in Schneider-2 cells into peptides similar to known neuropeptides. Two of the peptides were similar to FXPRL-amides (pyrokinins) and to the ecdysis-triggering hormone, respectively. The former displayed myostimulatory activity in a bioassay on the cockroach hyperneural muscle preparation, as well as in the Drosophila heart muscle assay. Hugin is expressed during the later half of embryogenesis and during larval stages in a subgroup of neurosecretory cells of the suboesophageal ganglion. Ubiquitous ectopic hugin expression resulted in larval death predominantly at or shortly after ecdysis from second to third instar, suggesting that at least one of the posttranslational cleavage products affects molting of the larva by interfering with the regulation of ecdysis.     

Changes in activity and expression of phosphofructokinase in different rat brain regions after basal forebrain cholinergic lesion

Selective lesion of rat basal forebrain by the cholinergic immunotoxin 192IgG-saporin was used as an animal model to address the question of whether the changes in cortical glucose metabolism observed in patients with Alzheimer's disease may be related to impaired cholinergic transmission. At different times after creating the immunolesion, the isoenzyme pattern and steady-state mRNA levels of the key glycolytic enzyme phosphofructokinase were determined in cortex, hippocampus, basal forebrain and nucleus caudatus. The loss of cholinergic input was accompanied by a persistent decrease in choline acetytransferase and acetylcholine esterase activities in the cortical target areas similar to the cholinergic malfunction seen in Alzheimer's dementia. The basal forebrain lesion induced by the immunotoxin resulted in a transient increase in phosphofructokinase activity peaking on day 7 after inducing the lesion in cortical areas. In parallel, an increased steady-state level of phosphofructokinase mRNA was determined by RT/real-time PCR and in situ hybridization. In contrast, analysis by western blotting and quantitative PCR revealed no changes in the phosphofructokinase isoenzyme pattern after immunolesion. It is concluded that common metabolic mechanisms may underlie the degenerative and repair processes in denervated rat brain and in the diseased Alzheimer's brain.