Encephalopathy caused by ablation of very long acyl chain ceramide synthesis may be largely due to reduced galactosylceramide levels

Sphingolipids (SLs) act as signaling molecules and as structural components in both neuronal cells and myelin. We now characterize the biochemical, histological, and behavioral abnormalities in the brain of a mouse lacking very long acyl (C22-C24) chain SLs. This mouse, which is defective in the ability to synthesize C22-C24-SLs due to ablation of ceramide synthase 2, has reduced levels of galactosylceramide (GalCer), a major component of myelin, and in particular reduced levels of non-hydroxy-C22-C24-GalCer and 2-hydroxy-C22-C24- GalCer. Noteworthy brain lesions develop with a time course consistent with a vital role for C22-C24-GalCer in myelin stability. Myelin degeneration and detachment was observed as was abnormal motor behavior originating from a subcortical region. Additional abnormalities included bilateral and symmetrical vacuolization and gliosis in specific brain areas, which corresponded to some extent to the pattern of ceramide synthase 2 expression, with astrogliosis considerably more pronounced than microglial activation. Unexpectedly, unidentified storage materials were detected in lysosomes of astrocytes, reminiscent of the accumulation that occurs in lysosomal storage disorders. Together, our data demonstrate a key role in the brain for SLs containing very long acyl chains and in particular GalCer with a reduction in their levels leading to distinctive morphological abnormalities in defined brain regions.     

Hsp90 and a tyrosine embedded in the Hsp90 recognition loop are required for the Fer tyrosine kinase activity

Hsp90 is a key regulator of tyrosine kinases activity and is therefore considered as a promising target for intervention with deregulated signaling pathways in malignant cells. Here we describe a novel Hsp90 client — the intracellular tyrosine kinase, Fer, which is subjected to a unique regulatory regime by this chaperone. Inhibition of Hsp90 activity led to proteasomal degradation of the Fer enzyme. However, circumventing the dependence of Fer accumulation on Hsp90, revealed the dependence of the Fer kinase activity and its ability to phosphorylate Stat3 on the chaperon, expressing the necessity of Hsp90 for its function. Mutation analysis unveiled a tyrosine (Tyr⁶¹⁶) embedded in the Hsp90 recognition loop, which is required for the kinase activity of Fer. Replacement of this tyrosine by phenylalanine (Y616F) disabled the auto-phosphorylation activity of Fer and abolished its ability to phosphorylate Stat3. Notably, surrounding the replaced Y616F with subtle mutations restored the auto and trans-phosphorylation activities of Fer suggesting that Y⁶¹⁶ is not itself an essential auto-phosphorylation site of the kinase. Taken together, our results portray Hsp90 and its recognition loop as novel positive regulators of the Fer tyrosine kinase stability and activity.     

Population cycles and changes in body size of the lynx in Alaska

The lynx Lynx canadensis is a common predator in the boreal forests of North America. Its population fluctuates during a 9- to 11-year cycle in synchrony with the population size of its main prey, the snowshoe hare Lepus americanus. Using adult museum specimens, we studied changes in skull (and hence body) size of the lynx in Alaska during the second half of the 20th century. The population cycle in Alaska averaged 9 years, similar to that reported in the neighbouring Yukon. Using harvest data of lynx as an estimate of population size, we found that skull size was negatively related to population size. This relationship was strongest not for the population density in the year of death (X), but for year X-3, a carry-over effect from the first year (or years) of life, indicating that conditions during the fast-growth years are determining body size. We suggest that the density-dependent effect is probably due to changes in food supply, either resulting from the adverse effects of competition or a possible diminished availability of food. Two skull parameters decreased significantly during the second half of the 20th century. We do not know the cause for the year effect and suggest that it might be due to a long-term change in the availability of prey. Canine size did not change during the study period, probably an indication that snowshoe hares maintained their status as the main prey of the lynx throughout the study period. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sample-based assessment of the microbial etiology of bovine necrotic vulvovaginitis

A semiquantitative evaluation of potential bacterial pathogens was correlated to the severity of lesions during an outbreak of bovine necrotic vulvovaginitis (BNVV) on an Israeli dairy herd. Bacteriologic examination of 287 vaginal swabs from 104 post-calving heifers showed a highly significant correlation between Porphyromonas levii colony forming unit numbers and the clinical scores of the lesions, when assessed by an ordinal regression statistical model. No such correlation was found for the other bacteria included in the study. Nineteen samples taken for virological examinations resulted negative for bovine herpes viruses 1, 2, 4 and 5. Thus the results of this study substantiate the essential role of P. levii in the etiology of BNVV and indicate that BHV4 is not required as a predisposing factor to the syndrome.     

Genetic ancestry,population sub-structure,and cardiovascular disease-related traits among African-American participants in the CARDIA Study

African-American populations are genetically admixed. Studies performed among unrelated individuals from ethnically admixed populations may be both vulnerable to confounding by population stratification, but offer an opportunity for efficiently mapping complex traits through admixture linkage disequilibrium. By typing 42 ancestry-informative markers and estimating genetic ancestry, we assessed genetic admixture and heterogeneity among African-American participants in the Coronary Artery Risk Development in Young Adults (CARDIA) cohort. We also assessed associations between individual genetic ancestry and several quantitative and binary traits related to cardiovascular risk. We found evidence of population sub-structure and excess inter-marker linkage disequilibrium, consistent with recent admixture. The estimated group admixture proportions were 78.1% African and 22.9% European, but differed according to geographic region. In multiple regression models, African ancestry was significantly associated with decreased total cholesterol, decreased LDL-cholesterol, and decreased triglycerides, and also with increased risk of insulin resistance. These observed associations between African ancestry and several lipid traits are consistent with the general tendency of individuals of African descent to have healthier lipid profiles compared to European-Americans. There was no association between genetic ancestry and hypertension, BMI, waist circumference, CRP level, or coronary artery calcification. These results demonstrate the potential for confounding of genetic associations with some cardiovascular disease-related traits in large studies involving US African-Americans.     

Mathematical model of excitation-contraction in a uterine smooth muscle cell

Uterine contractility is generated by contractions of myometrial smooth muscle cells (SMCs) that compose most of the myometrial layer of the uterine wall. Calcium ion (Ca²⁺) entry into the cell can be initiated by depolarization of the cell membrane. The increase in the free Ca²⁺ concentration within the cell initiates a chain of reactions, which lead to formation of cross bridges between actin and myosin filaments, and thereby the cell contracts. During contraction the SMC shortens while it exerts forces on neighboring cells. A mathematical model of myometrial SMC contraction has been developed to study this process of excitation and contraction. The model can be used to describe the intracellular Ca²⁺ concentration and stress produced by the cell in response to depolarization of the cell membrane. The model accounts for the operation of three Ca²⁺ control mechanisms: voltage-operated Ca²⁺ channels, Ca²⁺ pumps, and Na⁺/Ca²⁺ exchangers. The processes of myosin light chain (MLC) phosphorylation and stress production are accounted for using the cross-bridge model of Hai and Murphy (Am J Physiol Cell Physiol 254: C99–C106, 1988) and are coupled to the Ca²⁺ concentration through the rate constant of myosin phosphorylation. Measurements of Ca²⁺, MLC phosphorylation, and force in contracting cells were used to set the model parameters and test its ability to predict the cell response to stimulation. The model has been used to reproduce results of voltage-clamp experiments performed in myometrial cells of pregnant rats as well as the results of simultaneous measurements of MLC phosphorylation and force production in human nonpregnant myometrial cells. cellular calcium control mechanisms; myometrial contractions; myosin light chain phosphorylation     

Have We Neglected the Role of Fetal Endothelium in Transplacental Transport?

Maternal‐to‐fetal transfer of nutrient and other substances occurs across the placental barrier (PB) which is made up of endothelial cells (EC) on the fetal side and the syncytiotrophoblast (STB) on the maternal side. Numerous studies were conducted to explore the transport characteristics across the STB layer, which is also considered as the major resistance for maternal‐to‐fetal exchange of materials. In contrast the layer of EC has received very little attention if at all. A recently developed viable co‐culture model of the PB revealed significant resistance of the EC layer for maternal‐to‐fetal transfer of glucose. This argues for a major contribution of the EC to overall transplacental transfer of nutrients. Accordingly, it is recommended to fill the void of knowledge and expand our understanding on the role of the feto‐placental endothelium for transplacental transport characteristics.     

A novel method for estimating the number of species within a region

Ecologists are often required to estimate the number of species in a region or designated area. A number of diversity indices are available for this purpose and are based on sampling the area using quadrats or other means, and estimating the total number of species from these samples. In this paper, a novel theory and method for estimating the number of species is developed. The theory involves the use of the Laplace method for approximating asymptotic integrals. The method is shown to be successful by testing random simulated datasets. In addition, several real survey datasets are tested, including forests that contain a large number (tens to hundreds) of tree species, and an aquatic system with a large number of fish species. The method is shown to give accurate results, and in almost all cases found to be superior to existing tools for estimating diversity.     

The Central Nervous System as Target of Bacillus anthracis Toxin Independent Virulence in Rabbits and Guinea Pigs

Infection of the central nervous system is considered a complication of Anthrax and was reported in humans and non-human primates. Previously we have reported that Bacillus anthracis possesses a toxin-independent virulent trait that, like the toxins, is regulated by the major virulence regulator, AtxA, in the presence of pXO2. This toxin-independent lethal trait is exhibited in rabbits and Guinea pigs following significant bacteremia and organ dissemination. Various findings, including meningitis seen in humans and primates, suggested that the CNS is a possible target for this AtxA-mediated activity. In order to penetrate into the brain tissue, the bacteria have to overcome the barriers isolating the CNS from the blood stream. Taking a systematic genetic approach, we compared intracranial (IC) inoculation and IV/SC inoculation for the outcome of the infection in rabbits/GP, respectively. The outstanding difference between the two models is exhibited by the encapsulated strain VollumΔpXO1, which is lethal when injected IC, but asymptomatic when inoculated IV/SC. The findings demonstrate that there is an apparent bottleneck in the ability of mutants to penetrate into the brain. Any mutant carrying either pXO1 or pXO2 will kill the host upon IC injection, but only those carrying AtxA either on pXO1 or in the chromosome in the background of pXO2 can penetrate into the brain following peripheral inoculation. The findings were corroborated by histological examination by H&E staining and immunofluorescence of rabbits'' brains following IV and IC inoculations. These findings may have major implications on future research both on B. anthracis pathogenicity and on vaccine development.