Spatial Analysis of Production by Macrophytes,Phytoplankton and Epiphyton in a Large River System under Different Water-Level Conditions

Relative contributions by macrophytes, epiphyton and phytoplankton to total primary production was estimated in a large (∼300 km²) widening of the St. Lawrence River (Canada), over a 2-year period with contrasting flows and water levels. Spatially-explicit estimates of whole-system production were obtained by combining field measurements with remotely sensed data and empirical models using GIS. Primary production and relative contributions of each producer type differed markedly between open-water and wetland habitats. Spatial differences within each habitat arose from interactions between physical factors including light, water depth, water transit times and wind stress. At the whole-system level, annual primary production represented 105 gC m⁻² y⁻¹, divided roughly equally among phytoplankton (34%), submerged macrophytes (27%), emergent macrophytes (23%) and epiphyton (16%). A 10% decrease in annual flows and 1-m decline in water levels between 2000 and 2001 resulted in a 50% loss of marsh habitat, a 60% increase in phytoplankton production in the open-water zone, and in the appearance of conspicuous filamentous algal mats. Low water levels induced substantial shifts in the spatial configuration and relative importance of primary producers although total river primary production remained stable between years.     

Genetic evidence of serum phosphate-independent functions of FGF-23 on bone

Maintenance of physiologic phosphate balance is of crucial biological importance, as it is fundamental to cellular function, energy metabolism, and skeletal mineralization. Fibroblast growth factor-23 (FGF-23) is a master regulator of phosphate homeostasis, but the molecular mechanism of such regulation is not yet completely understood. Targeted disruption of the Fgf-23 gene in mice (Fgf-23-/-) elicits hyperphosphatemia, and an increase in renal sodium/phosphate co-transporter 2a (NaPi2a) protein abundance. To elucidate the pathophysiological role of augmented renal proximal tubular expression of NaPi2a in Fgf-23-/- mice and to examine serum phosphate-independent functions of Fgf23 in bone, we generated a new mouse line deficient in both Fgf-23 and NaPi2a genes, and determined the effect of genomic ablation of NaPi2a from Fgf-23-/- mice on phosphate homeostasis and skeletal mineralization. Fgf-23-/-/NaPi2a-/- double mutant mice are viable and exhibit normal physical activities when compared to Fgf-23-/- animals. Biochemical analyses show that ablation of NaPi2a from Fgf-23-/- mice reversed hyperphosphatemia to hypophosphatemia by 6 weeks of age. Surprisingly, despite the complete reversal of serum phosphate levels in Fgf-23-/-/NaPi2a-/-, their skeletal phenotype still resembles the one of Fgf23-/- animals. The results of this study provide the first genetic evidence of an in vivo pathologic role of NaPi2a in regulating abnormal phosphate homeostasis in Fgf-23-/- mice by deletion of both NaPi2a and Fgf-23 genes in the same animal. The persistence of the skeletal anomalies in double mutants suggests that Fgf-23 affects bone mineralization independently of systemic phosphate homeostasis. Finally, our data support (1) that regulation of phosphate homeostasis is a systemic effect of Fgf-23, while (2) skeletal mineralization and chondrocyte differentiation appear to be effects of Fgf-23 that are independent of phosphate homeostasis.     

Analysis of the functional maturation of olfactory neurons in chicks before and after birth

There has been indirect evidence that the olfactory system of mammals could be functional shortly before birth. Taking advantage of the accessibility of bird embryos, we studied the functional maturation of the olfactory mucosa during embryonic development in birds. Using the combination of electrophysiological EOG recordings and immunohistochemical studies, it was possible to directly demonstrate for the first time that the olfactory system is functional during embryogenesis from embryonic day (ED) 13 and that the beginning of olfactory function coincides with the first localization of the calcium dependent calmodulin kinase II (CaMKIIalpha) in the dendrites of the olfactory receptor neurons. CaMKII and olfactory receptor genes are expressed much earlier in olfactory neurons, both involved in the sensory transduction, but the pattern of expression of CaMKIIalpha changes during the ontogenesis. The increase of EOG amplitude between ED13 and ED15 also coincides with the increase of the number of neurons presenting the dendritic localization of CaMKIIalpha. These results suggest that the enzyme CaMKII might play a role in the functional maturation of the olfactory mucosa.     

Post‐translational methylations of the archaeal Mre11:Rad50 complex throughout the DNA damage response

The Mre11:Rad50 complex is central to DNA double strand break repair in the Archaea and Eukarya, and acts through mechanical and nuclease activities regulated by conformational changes induced by ATP binding and hydrolysis. Despite the widespread use of Mre11 and Rad50 from hyperthermophilic archaea for structural studies, little is known in the regulation of these proteins in the Archaea. Using purification and mass spectrometry approaches allowing nearly full sequence coverage of both proteins from the species Sulfolobus acidocaldarius, we show for the first time post‐translational methylation of the archaeal Mre11:Rad50 complex. Under basal growth conditions, extensive lysine methylations were identified in Mre11 and Rad50 dynamic domains, as well as methylation of a few aspartates and glutamates, including a key Mre11 aspartate involved in nuclease activity. Upon γ‐irradiation induced DNA damage, additional methylated residues were identified in Rad50, notably methylation of Walker B aspartate and glutamate residues involved in ATP hydrolysis. These findings strongly suggest a key role for post‐translational methylation in the regulation of the archaeal Mre11:Rad50 complex and in the DNA damage response.     

Seasonal and inter-annual variations of nitrogen diagenesis in the sediments of a recently impounded basin

The Méry-sur-Oise (France) storage reservoir is an artificial basin of 9 m average depth, fed by water from the river Oise with a mean residence time of about 4 days. Sediments are accumulating at a rate of about 0.7 cm/month. In the sediments, two fractions of organic nitrogen with different rates of bacterial degradation could be distinguished, one associated with fresh phytoplankton, the other made of detrital and more refractory compounds. The fluxes of oxygen, nitrate and ammonium across the sediment-water interface were measured with a bell-jar system at different seasons during a 3 year period following flooding of the basin. The measurements show clear seasonal variations in relation with the variations of temperature and input of fresh phytoplanktonic material to the sediment. In addition, a long term trend of increasing ammonium was observed. Measurements were also carried out after dredging of all accumulated sediments of the basin. They showed a considerable reduction of the flux of nitrate to the sediments and a significant reduction of the flux of ammonium to the water column.These results are interpreted in the light of a non stationary model of N diagenesis in accumulating sediments. This model is able to predict at least the general trends of benthic N cycling of basins during the early stage of their ecological succession.     

A multi-recombination model for the mtDNA rearrangements seen in maize cmsT regenerated plants

Regeneration of plants from maize cytoplasmic male sterile type T (cmsT) callus tissue culture promotes, in some instances, genetic variability in their mitochondrial genomes. These mutations have been analyzed in various cmsT regenerated plants that have or have not regained the male fertile phenotype. A unique multi-recombination model explains the various mitochondrial genome rearrangements. First, recombination involving two different sets of direct repeats gives rise to subgenomic recombinant circles. Second, intermolecular recombination between some selected subgenomes gives rise to a new rearranged master chromosome. The consequence of these events is the formation of a new master chromosome containing sequence deletions and duplications when compared to the progenitor. This new mitochondrial genome seems stable, although it does not contain the entire genetic complexity of the progenitor.     

Transposition of Tn5367 in Mycobacterium marinum,using a conditionally recombinant mycobacteriophage

Mycobacterium marinum is a close relative of the obligate human pathogen Mycobacterium tuberculosis. As with M. tuberculosis, M. marinum causes intracellular infection of poikilothermic vertebrates and skin infection in humans. It is considered a valid model organism for the study of intracellular pathogenesis of mycobacteria. Low transformation efficiencies for this species have precluded approaches using mutant libraries in pathogenesis studies. We have adapted the conditionally replicating mycobacteriophage phAE94, originally developed as a transposon mutagenesis tool for M. tuberculosis, to meet the specific requirements of M. marinum. Conditions permissive for phage replication in M. tuberculosis facilitated highly efficient transposon delivery in M. marinum. Using this technique we succeeded in generating a representative mutant library of this species, and we conclude that TM4-derived mycobacteriophages are temperature-independent suicide vectors for M. marinum.     

sst2 Somatostatin receptor inhibits cell proliferation through Ras-, Rap1-, and B-Raf-dependent ERK2 activation

The G protein-coupled sst2 somatostatin receptor is a critical negative regulator of cell proliferation. sstII prevents growth factor-induced cell proliferation through activation of the tyrosine phosphatase SHP-1 leading to induction of the cyclin-dependent kinase inhibitor p27Kip1. Here, we investigate the signaling molecules linking sst2 to p27Kip1. In Chinese hamster ovary-DG-44 cells stably expressing sst2 (CHO/sst2), the somatostatin analogue RC-160 transiently stimulates ERK2 activity and potentiates insulin-stimulated ERK2 activity. RC-160 also stimulates ERK2 activity in pancreatic acini isolated from normal mice, which endogenously express sst2, but has no effect in pancreatic acini derived from sst2 knock-out mice. RC-160-induced p27Kip1 up-regulation and inhibition of insulin-dependent cell proliferation are both prevented by pretreatment of CHO/sst2 cells with the MEK1/2 inhibitor PD98059. In addition, using dominant negative mutants, we show that sst2-mediated ERK2 stimulation is dependent on the pertussis toxin-sensitive Gi/o protein, the tyrosine kinase Src, both small G proteins Ras and Rap1, and the MEK kinase B-Raf but is independent of Raf-1. Phosphatidylinositol 3-kinase (PI3K) and both tyrosine phosphatases, SHP-1 and SHP-2, are required upstream of Ras and Rap1. Taken together, our results identify a novel mechanism whereby a Gi/o protein-coupled receptor inhibits cell proliferation by stimulating ERK signaling via a SHP-1-SHP-2-PI3K/Ras-Rap1/B-Raf/MEK pathway.     

Are Treponema pallidum Specific Rapid and Point-of-Care Tests for Syphilis Accurate Enough for Screening in Resource Limited Settings? Evidence from a Meta-Analysis

Background

Rapid and point-of-care (POC) tests for syphilis are an invaluable screening tool, yet inadequate evaluation of their diagnostic accuracy against best reference standards limits their widespread global uptake. To fill this gap, a systematic review and meta-analysis was conducted to evaluate the sensitivity and specificity of rapid and POC tests in blood and serum samples against Treponema pallidum (TP) specific reference standards.

Methods

Five electronic databases (1980–2012) were searched, data was extracted from 33 articles, and Bayesian hierarchical models were fit.

Results

In serum samples, against a TP specific reference standard point estimates with 95% credible intervals (CrI) for the sensitivities of popular tests were: i) Determine, 90.04% (80.45, 95.21), ii) SD Bioline, 87.06% (75.67, 94.50), iii) VisiTect, 85.13% (72.83, 92.57), and iv) Syphicheck, 74.48% (56.85, 88.44), while specificities were: i) Syphicheck, 99.14% (96.37, 100), ii) Visitect, 96.45% (91.92, 99.29), iii) SD Bioline, 95.85% (89.89, 99.53), and iv) Determine, 94.15% (89.26, 97.66). In whole blood samples, sensitivities were: i) Determine, 86.32% (77.26, 91.70), ii) SD Bioline, 84.50% (78.81, 92.61), iii) Syphicheck, 74.47% (63.94, 82.13), and iv) VisiTect, 74.26% (53.62, 83.68), while specificities were: i) Syphicheck, 99.58% (98.91, 99.96), ii) VisiTect, 99.43% (98.22, 99.98), iii) SD Bioline, 97.95%(92.54, 99.33), and iv) Determine, 95.85% (92.42, 97.74).

Conclusions

Rapid and POC treponemal tests reported sensitivity and specificity estimates comparable to laboratory-based treponemal tests. In resource limited settings, where access to screening is limited and where risk of patients lost to follow up is high, the introduction of these tests has already been shown to improve access to screening and treatment to prevent stillbirths and neonatal mortality due to congenital syphilis. Based on the evidence, it is concluded that rapid and POC tests are useful in resource limited settings with poor access to laboratories or screening for syphilis.     

Micrometric segregation of fluorescent membrane lipids: relevance for endogenous lipids and biogenesis in erythrocytes

Micrometric membrane lipid segregation is controversial. We addressed this issue in attached erythrocytes and found that fluorescent boron dipyrromethene (BODIPY) analogs of glycosphingolipids (GSLs) [glucosylceramide (BODIPY-GlcCer) and monosialotetrahexosylganglioside (GM1BODIPY)], sphingomyelin (BODIPY-SM), and phosphatidylcholine (BODIPY-PC inserted into the plasma membrane spontaneously gathered into distinct submicrometric domains. GM1BODIPY domains colocalized with endogenous GM1 labeled by cholera toxin. All BODIPY-lipid domains disappeared upon erythrocyte stretching, indicating control by membrane tension. Minor cholesterol depletion suppressed BODIPY-SM and BODIPY-PC but preserved BODIPY-GlcCer domains. Each type of domain exchanged constituents but assumed fixed positions, suggesting self-clustering and anchorage to spectrin. Domains showed differential association with 4.1R versus ankyrin complexes upon antibody patching. BODIPY-lipid domains also responded differentially to uncoupling at 4.1R complexes [protein kinase C (PKC) activation] and ankyrin complexes (in spherocytosis, a membrane fragility disease). These data point to micrometric compartmentation of polar BODIPY-lipids modulated by membrane tension, cholesterol, and differential association to the two nonredundant membrane:spectrin anchorage complexes. Micrometric compartmentation might play a role in erythrocyte membrane deformability and fragility.