Key Features of Intertidal Food Webs That Support Migratory Shorebirds

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web.The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.     

Opposite Roles of NMDA Receptors in Relapsing and Primary Progressive Multiple Sclerosis

Synaptic transmission and plasticity mediated by NMDA receptors (NMDARs) could modulate the severity of multiple sclerosis (MS). Here the role of NMDARs in MS was first explored in 691 subjects carrying specific allelic variants of the NR1 subunit gene or of the NR2B subunit gene of this glutamate receptor. The analysis was replicated for significant SNPs in an independent sample of 1548 MS subjects. The C allele of rs4880213 was found to be associated with reduced NMDAR-mediated cortical excitability, and with increased probability of having more disability than the CT/TT MS subjects. MS severity was higher in the CC group among relapsing-remitting MS (RR-MS) patients, while primary progressive MS (PP-MS) subjects homozygous for the T allele had more pronounced clinical worsening. Mean time to first relapse, but not to an active MRI scan, was lower in the CC group of RR-MS patients, and the number of subjects with two or more clinical relapses in the first two years of the disease was higher in CC compared to CT/TT group. Furthermore, the percentage of relapses associated with residual disability was lower in subjects carrying the T allele. Lesion load at the MRI was conversely unaffected by the C or T allele of this SNP in RR-MS patients. Axonal and neuronal degeneration at the optical coherence tomography was more severe in the TT group of PP-MS patients, while reduced retinal nerve fiber thickness had less consequences on visual acuity in RR-MS patients bearing the T allele. Finally, the T allele was associated with preserved cognitive abilities at the Rao’s brief repeatable neuropsychological battery in RR-MS. Signaling through glutamate NMDARs enhances both compensatory synaptic plasticity and excitotoxic neurodegeneration, impacting in opposite ways on RR-MS and PP-MS pathophysiological mechanisms.     

A new simple fluorimetric method to assay cytosolic ATP content: application to durum wheat seedlings to assess modulation of mitochondrial potassium channel and uncoupling protein activity under hyperosmotic stress

The assays commonly used to determine ATP content in biological samples generally measure total cellular ATP content, but not the different subcellular pools. In this study a new simple method for measuring ATP content in a cytosol-enriched fraction (CEF) was developed, based on a rapid cytosolic ATP extraction (by an isotonic grinding medium that preserves organelle integrity) and its detection monitoring the NADPH fluorescence generated via hexokinase/glucose-6-phosphate dehydrogenase coupled reactions. Four protocols, differing for timing of NADPH generation and for either the presence or absence of some inhibitors of ATP and NADPH metabolism, were compared by determining CEF-ATP, as well as total ATP, in durum wheat (Triticum durum Desf.) etiolated seedlings. The best protocol was the one adopting both simultaneous NADPH generation and use of inhibitors during tissue homogenization. This protocol also showed higher performance than the classical trichloroacetic acid extraction. Using the new method, CEF-ATP content was assessed in control, salt- and osmotic-stressed seedlings, resulting 2.68 ± 0.04, 1.69 ± 0.12 (?40%) and 1.35 ± 0.16 (?50%) μmol/g dry weight, respectively. Finally, the effects of this stress-dependent decrease of cytosolic ATP were evaluated with respect to a possible modulation of two mitochondrial energy-dissipating systems, the uncoupling protein (PUCP) and the K⁺ channel (PmitoK_ATP), both inhibited by cytosolic ATP. Experiments carried out at different physiological ATP concentrations suggest that the decreased cytosolic ATP content occurring under hyperosmotic stress may contribute to attenuate inhibition of PmitoK_ATP, thus promoting its activity (up to about 90%), but not of PUCP, that appears to lose ATP sensitivity under stress condition.     

Self‐rescue of an EXTENSIN mutant reveals alternative gene expression programs and candidate proteins for new cell wall assembly in Arabidopsis

Plants encode a poorly understood superfamily of developmentally expressed cell wall hydroxyproline‐rich glycoproteins (HRGPs). One, EXTENSIN3 (EXT3) of the 168 putative HRGPs, is critical in the first steps of new wall assembly, demonstrated by broken and misplaced walls in its lethal homozygous mutant. Here we report the findings of phenotypic (not genotypic) revertants of the ext3 mutant and in‐depth analysis including microarray and qRT‐PCR (polymerase chain reaction). The aim was to identify EXT3 substitute(s), thus gaining a deeper understanding of new wall assembly. The data show differential expression in the ext3 mutant that included 61% (P ≤ 0.05) of the HRGP genes, and ability to self‐rescue by reprogramming expression. Independent revertants had reproducible expression networks, largely heritable over the four generations tested, with some genes displaying transgenerational drift towards wild‐type expression levels. Genes for nine candidate regulatory proteins as well as eight candidate HRGP building materials and/or facilitators of new wall assembly or maintenance, in the (near) absence of EXT3 expression, were identified. Seven of the HRGP fit the current model of EXT function. In conclusion, the data on phenotype comparisons and on differential expression of the genes‐of‐focus provide strong evidence that different combinations of HRGPs regulated by alternative gene expression networks, can make functioning cell walls, resulting in (apparently) normal plant growth and development. More broadly, this has implications for interpreting the cause of any mutant phenotype, assigning gene function, and genetically modifying plants for utilitarian purposes.     

Antimicrobial Combinations against Pan-Resistant Acinetobacter baumannii Isolates with Different Resistance Mechanisms

The study investigated the effect of antibiotic combinations against 20 clinical isolates of A. baumannii (seven colistin-resistant and 13 colistin-susceptible) with different resistance mechanisms. Clinical data, treatment, and patient mortality were evaluated. The following methods were used: MIC, PCRs, and outer membrane protein (OMP) analysis. Synergy was investigated using the checkerboard and time-kill methods. Clonality was evaluated by PFGE. Based on clonality, the whole genome sequence of six A. baumannii isolates was analyzed. All isolates were resistant to meropenem, rifampicin, and fosfomycin. OXA-23 and OXA-143 were the most frequent carbapenemases found. Four isolates showed loss of a 43kDa OMP_. The colistin-susceptible isolates belonged to different clones and showed the highest synergistic effect with fosfomycin-amikacin. Among colistin-resistant isolates, the highest synergistic effect was observed with the combinations of colistin-rifampicin followed by colistin-vancomycin. All colistin-resistant isolates harbored bla_OXA-23-like and belonged to CC113. Clinical and demographic data were available for 18 of 20 patients. Fourteen received treatment and eight patients died during treatment. The most frequent site of infection was the blood in 13 of 14 patients. Seven patients received vancomycin plus an active drug against A. baumannii; however, mortality did not differ in this group. The synergistic effect was similar for colistin-susceptible isolates of distinct clonal origin presenting with the same resistance mechanism. Overall mortality and death during treatment was high, and despite the high synergism in vitro with vancomycin, death did not differ comparing the use or not of vancomycin plus an active drug against A. baumannii.     

Relative sea‐level change regulates organic carbon accumulation in coastal habitats

Because coastal habitats store large amounts of organic carbon (C_org), the conservation and restoration of these habitats are considered to be important measures for mitigating global climate change. Although future sea‐level rise is predicted to change the characteristics of these habitats, its impact on their rate of C_org sequestration is highly uncertain. Here we used historical depositional records to show that relative sea‐level (RSL) changes regulated C_org accumulation rates in boreal contiguous seagrass–saltmarsh habitats. Age–depth modeling and geological and biogeochemical approaches indicated that C_org accumulation rates varied as a function of changes in depositional environments and habitat relocations. In particular, C_org accumulation rates were enhanced in subtidal seagrass meadows during times of RSL rise, which were caused by postseismic land subsidence and climate change. Our findings identify historical analogs for the future impact of RSL rise driven by global climate change on rates of C_org sequestration in coastal habitats.     

Presynaptic regulation of acetylcholine release in the CNS

The release of ACh appears to be under the control of autoreceptors localized on cholinergic nerve terminals. Moreover, the process can be regulated by transmitters other than ACh or by modulators either through receptor-mediated or carrier-mediated mechanisms. In this chapter we report on our recent results concerning the regulation of the release of ACh by ACh itself, 5-HT and GABA in the rat hippocampus. In particular it will be shown: 1) that the release of the cholinergic transmitter can be inhibited through muscarinic receptors of the M3 subtype; 2) that 5-HT can interact with ACh by depressing ACh release through the activation of receptors of the 5-HT1B subtype; 3) that the release of ACh can be enhanced by GABA by a novel mechanism involving a selective penetration of the amino acid into the cholinergic terminals.     

Sialic Acid Derivatives and their Distribution in Rat Sublingual Gland Acini during Pre- and Post-natal Development

Sialoglycoconjugates in rat sublingual gland acinar cells, at different stages of pre- and post-natal development, were investigated in situ with specific lectins and by the selective removal of terminal sialic acids. Cleavage of acetyl substituents sited in the pyranose ring and/or polyhydroxyl side chain was used as an additional means of characterising the glycoconjugates. The first expression of terminal sialic acid linked to -galactose was found at gestational day 17 and progressive different derivatives were observed. The terminal disaccharide sialic acid-N-acetylgalactosamine was constantly visualized in the sublingual gland from gestational day 18. In both terminal disaccharides, sialic acids were characterized by variable degrees of acetylation and were found to be highly packaged and responsible for the hydration coat. The complex data obtained indicated that the sublingual gland is characterized by a marked fluctuation of complex sialoglycoconjugates that differ from those in the submandibular gland of the same species.     

Docking-dependent regulation of the Rb tumor suppressor protein by Cdk4

Phosphorylation of target proteins by cyclin D1-Cdk4 requires both substrate docking and kinase activity. In addition to the ability of cyclin D1-Cdk4 to catalyze the phosphorylation of consensus sites within the primary amino acid sequence of a substrate, maximum catalytic activity requires the enzyme complex to anchor at a site remote from the phospho-acceptor site. A novel Cdk4 docking motif has been defined within a stretch of 19 amino acids from the C-terminal domain of the Rb protein that are essential for Cdk4 binding. Mutation or deletion of the docking motif prevents Cdk4-dependent phosphorylation of full-length Rb protein or C-terminal Rb fragments in vitro and in cells, while a peptide encompassing the Cdk4 docking motif specifically inhibits Cdk4-dependent phosphorylation of Rb. Cyclin D1-Cdk4 can overcome the growth-suppressive activity of Rb in both cell cycle progression and colony formation assays; however, while mutants of Rb in which the Cdk4 docking site has been either deleted or mutated retain growth suppressor activity, they are resistant to inactivation by cyclin D1-Cdk4. Finally, binding of Cdk4 to its docking site can inhibit cleavage of exogenous and endogenous Rb in response to distinct apoptotic signals. The Cdk4 docking motif in Rb gives insight into the mechanism by which enzyme specificity is ensured and highlights a role for Cdk4 docking in maintaining the Rb protein in a form that favors cell survival rather than apoptosis.