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.     

Alpha- and beta- cleavages of the amino-terminus of the cellular prion protein

It is commonly assumed that the physiological isoform of prion protein, PrP(C), is cleaved during its normal processing between residues 111/112, whereas the pathogenic isoform, PrP(Sc), is cleaved at an alternate site in the octapeptide repeat region around position 90. Here we demonstrated both in cultured cells and in vivo, that PrP(C) is subject to a complex set of post-translational processing with the molecule being cleaved upstream of position 111/112, in the octapeptide repeat region or at position 96. PrP has therefore two main cleavage sites that we decided to name alpha and beta. Cleavage of PrP(C) at these sites leads us to re-evaluate the function of both N- and C-terminus fragments thus generated.     

The spatial organization of proton and lactate transport in a rat brain tumor

Tumors create a heterogeneous acidic microenvironment which assists their growth and which must be taken into account in the design of drugs and their delivery. In addition, the acidic extracellular pH (pHe) is itself exploited in several experimental techniques for drug delivery. The way the acidity is created is not clear. We report here the spatial organization of key proton-handling proteins in C6 gliomas in rat brain. The mean profiles across the tumor rim of the Na+/H+ exchanger NHE1, and the lactate-H+ cotransporter MCT1, both showed peaks. NHE1, which is important for extension and migration of cells in vitro, showed a peak 1.55 times higher than in extratumoural tissue at 0.33 mm from the edge. MCT1 had a broader peak, further into the tumor (maximum 1.76 fold at 1.0 mm from the edge). In contrast, MCT4 and the carbonic anhydrase CAIX, which are associated with hypoxia, were not significantly upregulated in the rim. The spatial distribution of MCT4 was highly correlated with that of CAIX, suggesting that their expression is regulated by the same factors. Since protons extruded by NHE1 diffuse away through extracellular clefts, NHE1 requires a continuous source of intracellular protons. From the stoichiometries of metabolic pathways that produce or consume H+, and the greater availability of glucose compared to oxygen in most parts of a tumor, we support the classic view that most of the net proton efflux from C6 gliomas originates in glycolytic formation of lactate and H+ inside the tumor, but add that some lactate is taken up into cells in the rim on MCT1, and some lactate diffuses away, leaving its associated protons available to re-enter cells for extrusion on NHE1. Therapeutic inhibition of NHE1, MCT1 or CAIX is predicted to affect different parts of a tumor.     

Revisited and large-scale synthesis and purification of the mutated and wild type neu/erbB-2 membrane-spanning segment.

Solid-phase syntheses of the hydrophobic peptides Neu(TM35) ((1)EQRASPVTFIIATVVGVLLFLILVVVVGILIKRRR(35)) and Neu*(TM35) ((1)EQRASPVTFIIATVEGVLLFLILVVVVGILIKRRR(35)), corresponding to the native and mutated (V15E) transmembrane domain of the neu/erbB-2 tyrosine kinase receptor, respectively, were accomplished using Fmoc chemistry. The use of a new resin and cleavage and purification conditions led to large increases in yields and peptide purity. Two (15)N-labelled versions of both wild type and mutated peptides were also synthesized. Approximately 20-40 mg of peptide was obtained using a small-scale synthesis, whereas ca 100 mg of pure peptide was collected on a medium scale. Peptide purity, as monitored by HPLC and mass spectrometry, ranged from 95 to 98% for the six peptides synthesized. Secondary structure as determined by UV circular dichroism (CD) in trifluoroethanol (TFE) showed ca 74% alpha-helical content for the native peptide and ca 63% for that bearing the mutation. Secondary structure of Neu(TM35) was retained in DMPC (dimyristoylphosphatidylcholine)/DCPC (dicaproylphosphatidylcholine) membrane bicelles, and evidences for dimers/oligomers in the lipid bilayer were found.     

Modelling marine community responses to climate‐driven species redistribution to guide monitoring and adaptive ecosystem‐based management

As a consequence of global climate‐driven changes, marine ecosystems are experiencing polewards redistributions of species – or range shifts – across taxa and throughout latitudes worldwide. Research on these range shifts largely focuses on understanding and predicting changes in the distribution of individual species. The ecological effects of marine range shifts on ecosystem structure and functioning, as well as human coastal communities, can be large, yet remain difficult to anticipate and manage. Here, we use qualitative modelling of system feedback to understand the cumulative impacts of multiple species shifts in south‐eastern Australia, a global hotspot for ocean warming. We identify range‐shifting species that can induce trophic cascades and affect ecosystem dynamics and productivity, and evaluate the potential effectiveness of alternative management interventions to mitigate these impacts. Our results suggest that the negative ecological impacts of multiple simultaneous range shifts generally add up. Thus, implementing whole‐of‐ecosystem management strategies and regular monitoring of range‐shifting species of ecological concern are necessary to effectively intervene against undesirable consequences of marine range shifts at the regional scale. Our study illustrates how modelling system feedback with only limited qualitative information about ecosystem structure and range‐shifting species can predict ecological consequences of multiple co‐occurring range shifts, guide ecosystem‐based adaptation to climate change and help prioritise future research and monitoring.