The prion protein family

Although the pivotal implication of the host-encoded Prion protein, PrP, in the neuropathology of transmissible spongiform encephalopathy is known for decades, its biological role remains mostly elusive. Genetic inactivation is one way to assess such issue but, so far, PrP-knockout mice did not help much. However, recent reports involving (1) further studies of these mice during embryogenesis, (2) knockdown experiments in Zebrafish and (3) knockdown of Shadoo, a protein with PrP-like functional domains, in PrP-knockout mice, all suggested a role of the Prion protein family in early embryogenesis. This view is challenged by the recent report that PrP/Shadoo knockout mice are healthy and fertile. Although puzzling, these apparently contradictory data may on the contrary help at deciphering the Prion protein family role through focusing scientific attention outside the central nervous system and by helping the identification of other loci involved in the genetic robustness associated with PrP.     

Characterization and genetic mapping of a new blood-flesh trait controlled by the single dominant locus DBF in peach

Anthocyanin-rich peaches, because of their antioxidant properties and their strong attractiveness to consumers, are increasingly considered in French peach varietal innovation programs that integrate plant genomics and classical breeding. In this study, we describe a new blood-flesh trait identified in the ‘Wu Yue Xian’ peach accession from China. ‘Wu Yue Xian’ exhibits a fully red mesocarp during the later stages of fruit development, both with green midrib leaf and normal growth of the tree. This blood-flesh phenotype clearly differs from that determined by a single recessive locus (bf) in ‘Harrow Blood’, a clone showing blood-flesh in both immature and mature fruit associated with red midrib leaf and reduced tree height. We have then provided genetic evidence that blood-flesh phenotype of ‘Wu Yue Xian’ was controlled by a single dominant locus, designated DBF (Dominant Blood-Flesh), in four successive families derived from this accession. A genetic linkage map of the blood-flesh parent (‘D6090’) of the fourth population was constructed, including 102 SSRs spanning a total distance of 562.3 cM in eight linkage groups. Whereas the bf locus is located to linkage group 4, we mapped DBF to the top of linkage group 5, thus proving that DBF and bf loci are not alleles. Among 64 predicted genes in the DBF region (505 kbp), three genes of the dihydroflavonol-4-reductase family were identified as good candidates for the control of the DBF trait. Furthermore, SSR markers flanking DBF, such as AMPP157 and AMPPG178, supply a good basis to implement marker-assisted selection for this trait.     

Reduced striatal ecto-nucleotidase activity in schizophrenia patients supports the “adenosine hypothesis”

Schizophrenia (SZ) is a major chronic neuropsychiatric disorder characterized by a hyperdopaminergic state. The hypoadenosinergic hypothesis proposes that reduced extracellular adenosine levels contribute to dopamine D₂ receptor hyperactivity. ATP, through the action of ecto-nucleotidases, constitutes a main source of extracellular adenosine. In the present study, we examined the activity of ecto-nucleotidases (NTPDases, ecto-5′-nucleotidase, and alkaline phosphatase) in the postmortem putamen of SZ patients (n = 13) compared with aged-matched controls (n = 10). We firstly demonstrated, by means of artificial postmortem delay experiments, that ecto-nucleotidase activity in human brains was stable up to 24 h, indicating the reliability of this tissue for these enzyme determinations. Remarkably, NTPDase-attributable activity (both ATPase and ADPase) was found to be reduced in SZ patients, while ecto-5′-nucleotidase and alkaline phosphatase activity remained unchanged. In the present study, we also describe the localization of these ecto-enzymes in human putamen control samples, showing differential expression in blood vessels, neurons, and glial cells. In conclusion, reduced striatal NTPDase activity may contribute to the pathophysiology of SZ, and it represents a potential mechanism of adenosine signalling impairment in this illness.     

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.     

PrPC regulates epidermal growth factor receptor function and cell shape dynamics in Neuro2a cells

The prion protein (PrP) plays a key role in prion disease pathogenesis. Although the misfolded and pathologic variant of this protein (PrP^SC) has been studied in depth, the physiological role of PrP^C remains elusive and controversial. PrP^C is a cell‐surface glycoprotein involved in multiple cellular functions at the plasma membrane, where it interacts with a myriad of partners and regulates several intracellular signal transduction cascades. However, little is known about the gene expression changes modulated by PrP^C in animals and in cellular models. In this article, we present PrP^C‐dependent gene expression signature in N2a cells and its implication in the most overrepresented functions: cell cycle, cell growth and proliferation, and maintenance of cell shape. PrP^C over‐expression enhances cell proliferation and cell cycle re‐entrance after serum stimulation, while PrP^C silencing slows down cell cycle progression. In addition, MAP kinase and protein kinase B (AKT) pathway activation are under the regulation of PrP^C in asynchronous cells and following mitogenic stimulation. These effects are due in part to the modulation of epidermal growth factor receptor (EGFR) by PrP^C in the plasma membrane, where the two proteins interact in a multimeric complex. We also describe how PrP^C over‐expression modulates filopodia formation by Rho GTPase regulation mainly in an AKT‐Cdc42‐N‐WASP‐dependent pathway.

     

Identification of RFLP and NBS/PK profiling markers for disease resistance loci in genetic maps of oats

Two of the domains most widely shared among R genes are the nucleotide binding site (NBS) and protein kinase (PK) domains. The present study describes and maps a number of new oat resistance gene analogues (RGAs) with two purposes in mind: (1) to identify genetic regions that contain R genes and (2) to determine whether RGAs can be used as molecular markers for qualitative loci and for QTLs affording resistance to Puccinia coronata. Such genes have been mapped in the diploid A. strigosa × A. wiestii (Asw map) and the hexaploid MN841801-1 × Noble-2 (MN map). Genomic and cDNA NBS-RGA probes from oat, barley and wheat were used to produce RFLPs and to obtain markers by motif-directed profiling based on the NBS (NBS profiling) and PK (PK profiling) domains. The efficiency of primers used in NBS/PK profiling to amplify RGA fragments was assessed by sequencing individual marker bands derived from genomic and cDNA fragments. The positions of 184 markers were identified in the Asw map, while those for 99 were identified in the MN map. Large numbers of NBS and PK profiling markers were found in clusters across different linkage groups, with the PK profiling markers more evenly distributed. The location of markers throughout the genetic maps and the composition of marker clusters indicate that NBS- and PK-based markers cover partly complementary regions of oat genomes. Markers of the different classes obtained were found associated with the two resistance loci, PcA and R-284B-2, mapped on Asw, and with five out of eight QTLs for partial resistance in the MN map. 53 RGA-RFLPs and 187 NBS/PK profiling markers were also mapped on the hexaploid map A. byzantina cv. Kanota × A. sativa cv. Ogle. Significant co-localization was seen between the RGA markers in the KO map and other markers closely linked to resistance loci, such as those for P. coronata and barley yellow dwarf virus (Bydv) that were previously mapped in other segregating populations.     

Folding and stability of outer membrane protein A (OmpA) from Escherichia coli in an amphipathic polymer, amphipol A8-35

Amphipols are a class of amphipathic polymers designed to maintain membrane proteins in aqueous solutions in the absence of detergents. Denatured β-barrel membrane proteins, like outer membrane proteins OmpA from Escherichia coli and FomA from Fusobacterium nucleatum, can be folded by dilution of the denaturant urea in the presence of amphipol A8-35. Here, the folding kinetics and stability of OmpA in A8-35 have been investigated. Folding is well described by two parallel first-order processes, whose half-times, ~5 and ~70 min, respectively, are independent of A8-35 concentration. The faster process contributed ~55–64 % to OmpA folding. Folding into A8-35 was faster than into dioleoylphosphatidylcholine bilayers and complete at ratios as low as ~0.17 g/g A8-35/OmpA, corresponding to ~1–2 A8-35 molecules per OmpA. Activation energies were determined from the temperature dependence of folding kinetics, monitored both by electrophoresis, which reports on the formation of stable OmpA tertiary structure, and by fluorescence spectroscopy, which reflects changes in the environment of tryptophan side chains. The two methods yielded consistent estimates, namely ~5–9 kJ/mol for the fast process and ~29–37 kJ/mol for the slow one, which is lower than is observed for OmpA folding into dioleoylphosphatidylcholine bilayers. Folding and unfolding titrations with urea demonstrated that OmpA folding into A8-35 is reversible and that amphipol-refolded OmpA is thermodynamically stable at room temperature. Comparison of activation energies for folding and unfolding in A8-35 versus detergent indicates that stabilization of A8-35-trapped OmpA against denaturation by urea is a kinetic, not a thermodynamic phenomenon.