Sexual transmission of the [Het-S] prion leads to meiotic drive in Podospora anserina

In the filamentous fungus Podospora anserina, two phenomena are associated with polymorphism at the het-s locus, vegetative incompatibility and ascospore abortion. Two het-s alleles occur naturally, het-s and het-S. The het-s encoded protein is a prion propagating as a self-perpetuating amyloid aggregate. When prion-infected [Het-s] hyphae fuse with [Het-S] hyphae, the resulting heterokaryotic cells necrotize. [Het-s] and [Het-S] strains are sexually compatible. When, however, a female [Het-s] crosses with [Het-S], a significant percentage of het-S spores abort, in a way similar to spore killing in Neurospora and Podospora. We report here that sexual transmission of the [Het-s] prion after nonisogamous mating in the reproductive cycle of Podospora is responsible for the killing of het-S spores. Progeny of crosses between isogenic strains with distinct wild-type or introduced, ectopic het-s/S alleles were cytologically and genetically analyzed. The effect of het-s/S overexpression, ectopic het-s/S expression, absence of het-s expression, loss of [Het-s] prion infection, and the distribution patterns of HET-s/S-GFP proteins were categorized during meiosis and ascospore formation. This study unveiled a het-S spore-killing system that is governed by dosage of and interaction between the [Het-s] prion and the HET-S protein. Due to this property of the [Het-s] prion, the het-s allele acts as a meiotic drive element favoring maintenance of the prion-forming allele in natural populations.     

A model for transport of glucose in adipose tissue to a microdialysis probe

A model is presented, describing diffusion of solutes (as glucose) through adipose tissue. The model is based on the well-known extraction equation for diffusion across capillary walls or across the membrane of microdialysis probes, but adapted for use in adipose tissue. Arguments are presented for a simple scheme in which the mean capillary concentration of a solute (i.e., glucose) is substituted for the interstitial fluid solute concentration in the extraction equation, as the driving force for diffusion of glucose from capillary to cell or from capillary to a microdialysis probe. The model is discussed by evaluating the results of previous studies by our group and others on the equilibrium concentration of glucose in a microdialysis probe, as well as the effect of insertion on recovery of glucose by the probe and the time it takes for glucose in adipose tissue to diffuse to the probe. The results of these studies are in good agreement with the predictions derived from the model: The equilibrium concentration of glucose in the microdialysis probe is equal to the capillary glucose concentration. Insertion effects can be explained by a lower glucose concentration around the probe because of inflammation (12-18 h) and by a slow increase in the number of functioning capillaries around the probe due to wound healing (4-6 days). Transport time of glucose from capillaries to a microdialysis probe is not more than a few seconds. Reported delay times in the literature are probably caused by an uneven distribution of blood glucose after a glucose challenge.     

Feasibility of thoracoscopic repair of esophageal atresia with distal fistula

Backgound/Purpose: Evaluation of the feasibility of thoracoscopic correction of esophageal atresia with distal fistula. Methods: Eight consecutive neonates with esophageal atresia and distal fistula were treated thoracoscopically. Mean birth weight was 3,048 g (range, 2,140 to 3,770). The patients were intubated endotracheally and placed in a [frac34] left prone position. Three cannulae were inserted along the inferior tip of the scapula. CO₂ was insufflated at a pressure of 5mm Hg and a flow of 0.5 L/min. The fistula was either clipped or ligated. The proximal esophagus was opened and an anastomosis was made over a 6F or 8F nasogastric tube with interrupted 5-0 Vicryl. Results: All procedures were completed thoracoscopically without major peroperative complications. The mean operating time was 198 minutes (range, 138 to 250). One patient had a major leak, resulting in a stormy postoperative course, but the leak healed on conservative treatment. This patient and 3 others had stenosis requiring dilatation, respectively, 3, 6, 12, and 1 times. The babies were fed after a median period of 8 days. The median hospital stay was 13 days. Conclusions: Thoracoscopic repair of esophageal atresia with distal fistula is feasible. Larger series are needed to determine the exact place of the thoracoscopic approach.     

Supratentorial tuber location and autism in tuberous sclerosis complex

The high rate of autism in tuberous sclerosis complex provides an opportunity to study the pathogenesis of autism. This study investigated the relationship between a DSM-IV diagnosis of autism and tuber location in a sample of 50 individuals with tuberous sclerosis complex. Chi-square analyses revealed no differences between individuals with autism (n = 15) and those without autism (n = 35) on the occurrence of tubers in the right or left frontal, occipital, parietal, or temporal regions. There were no differences between the two groups in the occurrence of tubers in subcortical or cortical regions. In the largest sample to date, these results fail to support the hypothesis that supratentorial tuber location is a marker for autism.     

NMR spectroscopic evaluation of cerebral metabolism in hydrocephalus: a review

Cerebral ischemia contributes to cerebral damage in hydrocephalus. Many studies have reported changes in cerebral blood flow and metabolism, supporting this hypothesis. Magnetic resonance spectroscopy (MRS) enables us to investigate cerebral metabolism in a non-invasive and longitudinal manner, thereby providing a promising way of evaluating pathophysiological changes in experimental and clinical hydrocephalus. In this review, the potential of 1H (proton) and 31P (phosphorus) MRS in the assessment of cerebral metabolism will be summarized, and a synopsis of in vitro and in vivo MRS studies in experimental and human hydrocephalus will be presented. Changes in high-energy phosphate metabolism, intracellular pH and lactate production in several MRS studies are presumed to reflect cerebral ischemia. In vivo information on neuronal damage, maturational delay and membrane phospholipid metabolism may also be derived from 1H and 31P MRS data. Technical, methodological and pathophysiological considerations, which are important for a correct interpretation and comparison of different MRS studies, will be discussed. Finally, we will draw some conclusions on the significance of these MRS findings and the applicability of MRS in the diagnosis and evaluation of clinical hydrocephalus.     

Parallel imaging performance as a function of field strength--an experimental investigation using electrodynamic scaling.

In this work, the dependence of parallel MRI performance on main magnetic field strength is experimentally investigated. Using the general framework of electrodynamic scaling, the B0-dependent behavior of the relevant radiofrequency fields at a single physical field strength of 7 T is studied. In the chosen implementation this is accomplished by adjusting the permittivity and conductivity of a homogeneous spherical phantom. With different mixing ratios of decane, ethanol, purified water, N-methylformamide, and sodium chloride, field strengths in the range of 1.5 to 11.5 T are mimicked. Based on sensitivity maps of an eight-coil receiver array, the field-dependent performance of parallel imaging is assessed in terms of the geometry factor g, which reflects noise enhancement in parallel imaging reconstruction. At low field strengths the SNR penalty was nearly independent of B0 and favorably low for 1D reduction factors up to between 3 and 4. At higher field strengths the transition between favorable and prohibitive parallel imaging conditions was found to shift toward higher feasible reduction factors. These findings are in good agreement with previous theoretical predictions. From this agreement it is concluded that parallel MRI at high B0 benefits specifically from onsetting far-field behavior of the involved radiofrequency fields.     

CARBAMYLATION OF ALKALINE MESENTERICOPEPTIDASE

The effects of carbamylation with potassium cyanate, and methylation with methyl p-nitrobenzene sulphonate on the mesentericopeptidase activity are studied. The treatment with potassium cyanate causes the enzyme to lose its activity towards ester substrates and casein. The specific reagent N-trans-cinnamoylimidazole does not acylate the active site in the carbamylated enzyme. The pH dependence of the rate of inactivation indicates that an ionizing group of pK = 7.3, probably the protonated imidazole group of the active site histidine, is involved in the reaction. The competitive inhibitor boric acid protects mesentericopeptidase against inactivation with potassium cyanate. These results suggest that the active site residues are modified in the unprotected enzyme. Sixty per cent of the enzyme activity toward N-acetyl-L-tyrosine ethyl ester was restored after treatment of the carbamylated mesentericopeptidase with 1 M hydroxylamine hydrochloride. Circular dichroism spectra show that the carbamylation does not change markedly the native protein conformation. Methyl p-nitrobenzene sulphonate does not methylate the active site histidine.     

Modular kinetic analysis of the adenine nucleotide translocator-mediated effects of palmitoyl-CoA on the oxidative phosphorylation in isolated rat liver mitochondria

To test whether long-chain fatty acyl-CoA esters link obesity with type 2 diabetes through inhibition of the mitochondrial adenine nucleotide translocator, we applied a system-biology approach, dual modular kinetic analysis, with mitochondrial membrane potential (Deltapsi) and the fraction of matrix ATP as intermediates. We found that 5 mumol/l palmitoyl-CoA inhibited adenine nucleotide translocator, without direct effect on other components of oxidative phosphorylation. Indirect effects depended on how oxidative phosphorylation was regulated. When the electron donor and phosphate acceptor were in excess, and the mitochondrial "work" flux was allowed to vary, palmitoyl-CoA decreased phosphorylation flux by 38% and the fraction of ATP in the medium by 39%. Deltapsi increased by 15 mV, and the fraction of matrix ATP increased by 46%. Palmitoyl-CoA had a stronger effect when the flux through the mitochondrial electron transfer chain was maintained constant: Deltapsi increased by 27 mV, and the fraction of matrix ATP increased 2.6 times. When oxidative phosphorylation flux was kept constant by adjusting the rate using hexokinase, Deltapsi and the fraction of ATP were not affected. Palmitoyl-CoA increased the extramitochondrial AMP concentration significantly. The effects of palmitoyl-CoA in our model system support the proposed mechanism linking obesity and type 2 diabetes through an effect on adenine nucleotide translocator.