Natural evidence for rapid abiogenic hydrothermal generation of CH4

Although recent hydrothermal experiments imply that abiogenic methane (CH4) generation from hydrothermal reduction of CO2 can occur, evidence from natural systems was still lacking. Based on the chemical and isotopic equilibrium signatures of low-temperature fumarolic gas discharges, we are able to provide hard evidence for its natural occurrence, namely in three subduction-related bi-phase hydrothermal systems of the Mediterranean, whose temperatures range from 260 to 470 degrees C. The attainment of equilibrium and the time spans of recent volcanic dormancy allowed us to calculate minimum rates for chemical and isotopic equilibration. These are significantly higher than those previously reported and might be due to the presence of a saturated water vapor phase in the investigated systems. The fact that nature provides conditions enabling relatively fast production of hydrocarbons from CO2 strongly supports the concerns that were recently raised from laboratory experiments. These address the use of the carbon isotope composition of reduced carbon in Archean sediments as a tracer of early life and the occurrence of CH4 on extraterrestrial planets as a bioindicator. In view of the potential role of abiogenic CH4 as a precursor of life, we also present an estimate of abiogenic hydrothermal CH4 fluxes throughout the Archean. It is not expected that these fluxes exceeded 80 Mt/yr during the past 4.0 Ga. This, however, would have been enough to facilitate HCN production on the prebiotic Earth. (C) 2007 Elsevier Ltd. All rights reserved.

Segmentation and grid generation for numerical simulations of vad connections with patient-specific data

Objectives: We are interested in the numerical simulation of the anastomotic region comprised between outflow canula of LVAD and the aorta. Segmenta¬tion, geometry reconstruction and grid generation from patient-specific data remain an issue because of the variable quality of DICOM images, in particular CT-scan (e.g. metallic noise of the device, non-aortic contrast phase). We pro¬pose a general framework to overcome this problem and create suitable grids for numerical simulations.Methods: Preliminary treatment of images is performed by reducing the level window and enhancing the contrast of the greyscale image using contrast-limited adaptive histogram equalization. A gradient anisotropic diffusion filter is applied to reduce the noise. Then, watershed segmentation algorithms and mathematical morphology filters allow reconstructing the patient geometry. This is done using the InsightToolKit library (www.itk.org). Finally the Vascular Model¬ing ToolKit (www.vmtk.org) and gmsh (www.geuz.org/gmsh) are used to create the meshes for the fluid (blood) and structure (arterial wall, outflow canula) and to a priori identify the boundary layers. The method is tested on five different patients with left ventricular assistance and who underwent a CT-scan exam.Results: This method produced good results in four patients. The anastomosis area is recovered and the generated grids are suitable for numerical simulations. In one patient the method failed to produce a good segmentation because of the small dimension of the aortic arch with respect to the image resolution.Conclusions: The described framework allows the use of data that could not be otherwise segmented by standard automatic segmentation tools. In particular the computational grids that have been generated are suitable for simulations that take into account fluid-structure interactions. Finally the presented method features a good reproducibility and fast application.

Are invasive marsh frogs (Pelophylax ridibundus) replacing the native P. lessonae /P. esculentus hybridogenetic complex in Western Europe? Genetic evidence from a field study.

The water-frog L-E system, widespread in Western Europe, comprises the pool frog Pelophylax lessonae and the hybridogenetic edible frog P. esculentus, which originated from hybridization between pool frogs and marsh frogs (P. ridibundus). In P. esculentus, the lessonae (L) genome is eliminated during meiosis and has to be gained anew each generation from a P. lessonae partner, while the ridibundus (R') genome is transmitted clonally. It therefore accumulates deleterious mutations, so that R'R' offspring from P. esculentus x P. esculentus crosses are normally unviable. This system is now threatened by invasive P. ridibundus (RR) imported from Eastern Europe and the Balkans. We investigated the genetic interactions between invasive marsh frogs and native water frogs in a Swiss wetland area, and used genetic data collected in the field to validate several components of a recently postulated mechanism of species replacement. We identified neo-ridibundus individuals derived from crosses between invasive ridibundus and native esculentus, as well as newly arisen hybridogenetic esculentus lineages stemming from crosses between invasive ridibundus (RR) and native lessonae (LL). As their ridibundus genomes are likely to carry less deleterious mutations, such lineages are expected to produce viable ridibundus offspring, contributing to species replacement. However, such crosses with invasive ridibundus only occurred at a limited scale; moreover, RR x LL crosses did not induce any introgression from the ridibundus to the lessonae genome. We did not find any ridibundus stemming from crosses between ancient esculentus lineages. Despite several decades of presence on the site, introduced ridibundus individuals only represent 15% of sampled frogs, and their spatial distribution seems shaped by specific ecological requirements rather than history of colonization. We therefore expect the three taxa to coexist stably in this area.

Cutting edge: IL-7 regulates the peripheral pool of adult ROR gamma+ lymphoid tissue inducer cells.

During fetal life, CD4(+)CD3(-) lymphoid tissue inducer (LTi) cells are required for lymph node and Peyer's patch development in mice. In adult animals, CD4(+)CD3(-) cells are found in low numbers in lymphoid organs. Whether adult CD4(+)CD3(-) cells are LTi cells and are generated and maintained through cytokine signals has not been directly addressed. In this study we show that adult CD4(+)CD3(-) cells adoptively transferred into neonatal CXCR5(-/-) mice induced the formation of intestinal lymphoid tissues, demonstrating for the first time their bona fide LTi function. Increasing IL-7 availability in wild-type mice either by IL-7 transgene expression or treatment with IL-7/anti-IL-7 complexes increased adult LTi cell numbers through de novo generation from bone marrow cells and increased the survival and proliferation of LTi cells. Our observations demonstrate that adult CD4(+)lineage(-) cells are LTi cells and that the availability of IL-7 determines the size of the adult LTi cell pool.

Functional analysis of disease-causing NR2E3 mutations

Purpose:We analyzed the transcriptional activity of disease-causing NR2E3 mutant proteins in a heterologous system. NR2E3 belongs to the nuclear receptor superfamily of transcription factors, characterized by evolutionary-conserved DNA-binding (DBD) and ligand-binding (LBD) domains. NR2E3 acts in concert with the transcription factors CRX and NRL to repress cone-specific genes and activate rod-specific genes in rod photoreceptors. During development, NR2E3 is also required to suppress cone cell generation from retinal progenitor cells. In humans, mutations in NR2E3 have been associated with the recessively inherited enhanced short wavelength sensitive (S-) cone syndrome (ESCS), the Goldman-Favre syndrome, and, more recently, with autosomal dominant retinitis pigmentosa (adRP). Methods:The different NR2E3 mutants were generated by QuickChangeR mutagenesis and analyzed by transfection in heterologous HEK293T cells. Results:In transactivation assays in HEK293T cells, the adRP-linked p.G56R mutant protein exhibited a more severe effect both in activation of a rhodopsin promoter reporter construct and in repression of M-opsin promoter reporter construct, than the ESCS-linked R76Q, R76W, G88V, R97H, R104Q, R104W mutants of the DBD. In contrast, the ESCS-linked p.R311Q mutant of the LBD behaved like the NR2E3 wild-type protein in these assays. By co-expressing the corepressors atrophin-1 and -2, a differential repression of the M-opsin promoter was observed in presence of the p.R311Q, p.R385P and p.M407K. Interestingly, corepressor expression also affected the activity of CRX, but not NRL, in both rhodopsin and M-opsin transactivation assays. Conclusions:Taken together, these in vitro results suggest a distinct disease mechanism for the adRP-linked mutation, but open the possibility of different mechanisms for the development of ESCS that is clinically characterized by important phenotypic variations.

Crocidura cossyrensis Contoli, 1989 (Mammalia, Soridiae): karyotype, biochemical genetics and hybridization experiments

Crocidura cossyrensis Contoli, 1989 (Mammalia, Soricidae): karyotype, biochemical genetics and hybridization experiments. - The shrew Crocidura cossyrensis Contoli, 1989 from Pantelleria (I), a Mediterranean island 100 km south of Sicily and 70 km west from Tunisia, was investigated in order to understand its origin and its relationship with C. russula from Tunisia, Morocco and Switzerland. With the exception of a single heterozygote centric fusion, C. cossyrensis had a karyotype identical with that of C russula from Tunisia (2N = 42, NF = 70 to 72), but it differed from C russula from Morocco and Switzerland (2N = 42, NF = 60). The former have 5-6 pairs of chromosomes with small arms that are acrocentric in the latter. Genetic comparisons with allozyme data revealed small genetic distance (0.04) between C cossyrensis and C russula from Tunisia. In contrast, this eastern clade (Tunisia and Pantelleria) is separated from the western clade (Switzerland and Morocco) by a genetic distance of 0.14. A hybridization experiment between shrews from Pantelleria and Switzerland lead rapidly to an F1 generation. From 12 F1 hybrids that were backcrossed, females reproduced normally, but none of the males did so. Concluding from the results, C. cossyrensis from Pantelleria and C. russula cf. agilis from Tunisia belong to the same taxon that may have reached the differentiation of a biological species within the C. russula group. More geographic samples are needed to determine the definitive taxonomic positions of these shrews.

Uncertainty of combined activity estimations

This paper discusses basic theoretical strategies used to deal with measurement uncertainties arising from different experimental situations. It attempts to indicate the most appropriate method of obtaining a reliable estimate of the quantity to be evaluated depending on the characteristics of the data available. The theoretical strategies discussed are supported by experimental detail, and the conditions and results have been taken from examples in the field of radionuclide metrology. Special care regarding the correct treatment of covariances is emphasized because of the unreliability of the results obtained if these are neglected

Inheritance of ductile and brittle structures in the development of large rock slope instabilities: Examples from western Norway

The high density of slope failures in western Norway is due to the steep relief and to the concentration of various structures that followed protracted ductile and brittle tectonics. On the 72 investigated rock slope instabilities, 13 were developed in soft weathered mafic and phyllitic allochthons. Only the intrinsic weakness of such rocks increases the susceptibility to gravitational deformation. In contrast, the gravitational structures in the hard gneisses reactivate prominent ductile or/and brittle fabrics. At 30 rockslides along cataclinal slopes, weak mafic layers of foliation are reactivated as basal planes. Slope-parallel steep foliation forms back-cracks of unstable columns. Folds are specifically present in the Storfjord area, together with a clustering of potential slope failures. Folding increases the probability of having favourably orientated planes with respect to the gravitational forces and the slope. High water pressure is believed to seasonally build up along the shallow-dipping Caledonian detachments and may contribute to destabilization of the rock slope upwards. Regional cataclastic faults localized the gravitational structures at 45 sites. The volume of the slope instabilities tends to increase with the amount of reactivated prominent structures and the spacing of the latter controls the size of instabilities.

Data bases for the assessment of medical technologies: examples from Europe.

The assessment of medical technologies has to answer several questions ranging from safety and effectiveness to complex economical, social, and health policy issues. The type of data needed to carry out such evaluation depends on the specific questions to be answered, as well as on the stage of development of a technology. Basically two types of data may be distinguished: (a) general demographic, administrative, or financial data which has been collected not specifically for technology assessment; (b) the data collected with respect either to a specific technology or to a disease or medical problem. On the basis of a pilot inquiry in Europe and bibliographic research, the following categories of type (b) data bases have been identified: registries, clinical data bases, banks of factual and bibliographic knowledge, and expert systems. Examples of each category are discussed briefly. The following aims for further research and practical goals are proposed: criteria for the minimal data set required, improvement to the registries and clinical data banks, and development of an international clearinghouse to enhance information diffusion on both existing data bases and available reports on medical technology assessments.

The role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at Arenal volcano, Costa Rica: evidence from clinopyroxene and spinel

The bulk composition of magma erupted from Volcan Arenal has remained nearly constant (SiO2 = 53.6-54.9 wt%; MgO = 5.0-4.5 wt%) during almost 30 years of continuous activity (1969-1996). None the less, clinopyroxene (cpx) phenocrysts and their spinel inclusions record a much more complex open-system evolution in which steady-state production of the erupted basaltic andesitic magma is linked to episodic injections of basalt into Arenal's magma conduit/reservoir system. High-resolution major element zoning profiles (electron microprobe) on a large number of phenocrysts (>14,000 analyses), tied to back-scattered electron (BSE) images, have been used to assess the compositional characteristics of the magmatic end members as well as the timing and dynamics of magma replenishment events. No two cpx phenocrysts have exactly the same zoning profile. The vast majority of our analyses record the crystallization of cpx (Cr2O3 < 0.12 wt%; Mg# = 65-79; Al/Ti = 2-7) from a liquid comparable to or more evolved than erupted magma compositions. However, half of all cpx grains are cored by high-Cr cpx (Cr2O3 = 0.2-0.72 wt%) or contain similar basaltic compositions as abrupt growth bands in phenocrysts with and without high-Cr cores; phenocrysts with high-Cr cpx occur throughout the ongoing activity. In a few cases, high-Cr cpx occurs very near the outer margin of the grain without an apparent growth hiatus, particularly in 1968/69 and 1992/93. The main conclusions are: (1) all basaltic andesitic lavas erupted at Arenal during the ongoing activity that began in July, 1968, are the products of magma mixing, (2) clinopyroxenes record multiple replenishment events of basaltic magma in contrast to the near constancy of erupted bulk compositions, (3) some phenocrysts preserve records of multiple interactions with basaltic magmas requiring magmatic processes to operate on time-scales shorter than residence times of some phenocrysts, (4) multiple occurrences of clinopyroxene with high-Cr rims suggest that basalt replenishment events have occurred with sub-decadal frequency and may predate eruption by months or less. From this we infer that Arenal volcano is underlain by a continuously active, small-volume magmatic reservoir maintained in quasi-steady state by basalt recharge over several decades. The monotony of erupting Arenal magmas implies that fractionation, recharge, ascent, and eruption are well balanced in order for magmas to be essentially uniform while containing phenocrysts with vastly different growth histories at the time of eruption.

Reliability of stable carbon and oxygen isotope compositions of pedogenic needle fibre calcite as environmental indicators: examples from Western Europe.

Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ(13)C values (-12.5 to-6.8 0/00 Vienna Pee Dee Belemnite (VPDB)) record the predominant C(3) vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ(18)O values (-7.8 to-3.40/00 VPDB) of all the NFC. Similar seasonal variations of δ(18)O values for monthly NFC samples from the Swiss sites and those of mean monthly δ(18)O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions.

Efficient generation of human alloantigen-specific CD4+ regulatory T cells from naive precursors by CD40-activated B cells.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) play an important role in the induction and maintenance of immune tolerance. Although adoptive transfer of bulk populations of Treg can prevent or treat T cell-mediated inflammatory diseases and transplant allograft rejection in animal models, optimal Treg immunotherapy in humans would ideally use antigen-specific rather than polyclonal Treg for greater specificity of regulation and avoidance of general suppression. However, no robust approaches have been reported for the generation of human antigen-specific Treg at a practical scale for clinical use. Here, we report a simple and cost-effective novel method to rapidly induce and expand large numbers of functional human alloantigen-specific Treg from antigenically naive precursors in vitro using allogeneic nontransformed B cells as stimulators. By this approach naive CD4(+)CD25(-) T cells could be expanded 8-fold into alloantigen-specific Treg after 3 weeks of culture without any exogenous cytokines. The induced alloantigen-specific Treg were CD45RO(+)CCR7(-) memory cells, and had a CD4(high), CD25(+), Foxp3(+), and CD62L (L-selectin)(+) phenotype. Although these CD4(high)CD25(+)Foxp3(+) alloantigen-specific Treg had no cytotoxic capacity, their suppressive function was cell-cell contact dependent and partially relied on cytotoxic T lymphocyte antigen-4 expression. This approach may accelerate the clinical application of Treg-based immunotherapy in transplantation and autoimmune diseases.

Genetic causes of transitions from sexual reproduction to asexuality in plants and animals.

The persistence of sexual reproduction in the face of competition from asexual invaders is more likely if asexual lineages are produced infrequently or have low fitness. The generation rate and success of new asexual lineages will be influenced by the proximate mechanisms underlying transitions to asexuality. As such, characterization of these mechanisms can help explain the distribution of reproductive modes among natural populations. Here, we synthesize the literature addressing proximate causes of transitions from sexual to asexual reproduction in plants and animals. In cyclical and facultatively asexual taxa, individual mutations can cause obligate asexuality. The evolution of asexuality in obligately sexual groups is more complex, requiring the simultaneous acquisition of two traits generally controlled by different genetic factors: unreduced gamete formation and spontaneous development of unfertilized gametes. At least three 'pre-adaptations' could favour transitions to obligate asexuality in obligate sexuals. First, linkage among loci affecting separate key components of asexuality facilitates its spread, with evidence for these linkage blocks in plants. Second, asexuality should evolve more readily in haplodiploids; support for this hypothesis comes from two examples where a single locus causes transitions to asexuality. Third, standing genetic variation for the production of unreduced gametes could facilitate transitions to asexuality, but whether the ability to produce unreduced gametes contributes to the evolution of obligate asexuality remains unclear. We close by reviewing the associations between asexuality, hybridization and polyploidy, and argue that current data suggest that hybridization is more likely to play a causal role in transitions to asexuality than polyploidy.