Modification of photosynthetic regulation in tomato overexpressing glutathione peroxidase

To investigate the function of glutathione peroxidase (GPX) in plants, we produced transgenic tomato plants overexpressing an eukaryotic selenium-independent GPX (GPX5). We show here that total GPX activity was increased by 50% in transgenic plants, when compared to control plants transformed with the binary vector without the insert (PZP111). A preliminary two-dimensional electrophoretic protein analysis of the GPX overexpressing plants showed notably a decrease in the accumulation of proteins identified as rubisco small subunit 1 and fructose-1,6-bisphosphate aldolase, two proteins involved in photosynthesis. These observations, together with the fact that in standard culture conditions, GPX-overexpressing plants were not phenotypically distinct from control plants prompted us to challenge the plants with a chilling treatment that is known to affect photosynthesis activity. We found that upon chilling treatment with low light level, photosynthesis was not affected in GPX-overexpressing plants while it was in control plants, as revealed by chlorophyll fluorescence parameters and fructose-1,6-biphosphatase activity. These results suggest that overexpression of a selenium-independent GPX in tomato plants modifies specifically gene expression and leads to modifications of photosynthetic regulation processes.     

Absence of the RGS9.Gbeta5 GTPase-activating complex in photoreceptors of the R9AP knockout mouse

Timely termination of the light response in retinal photoreceptors requires rapid inactivation of the G protein transducin. This is achieved through the stimulation of transducin GTPase activity by the complex of the ninth member of the regulator of G protein signaling protein family (RGS9) with type 5 G protein beta subunit (Gbeta5). RGS9.Gbeta5 is anchored to photoreceptor disc membranes by the transmembrane protein, R9AP. In this study, we analyzed visual signaling in the rods of R9AP knockout mice. We found that light responses from R9AP knockout rods were very slow to recover and were indistinguishable from those of RGS9 or Gbeta5 knockout rods. This effect was a consequence of the complete absence of any detectable RGS9 from the retinas of R9AP knockout mice. On the other hand, the level of RGS9 mRNA was not affected by the knockout. These data indicate that in photoreceptors R9AP determines the stability of the RGS9.Gbeta5 complex, and therefore all three proteins, RGS9, Gbeta5 , and R9AP, are obligate members of the regulatory complex that speeds the rate at which transducin hydrolyzes GTP.     

Neuron-glia interactions in the hypothalamus

The supraoptic (SON) and paraventricular (PVN) magnocellular nuclei of the hypothalamus undergo reversible anatomical remodeling under conditions of intense secretion of neurohypophysial hormones, such as lactation and chronic dehydration. This morphological plasticity is characterized by a pronounced reduction in astrocytic coverage of neurons, which results in an increased number and extent of directly juxtaposed somatic and dendritic surfaces. As a consequence, astrocyte-mediated clearance of glutamate from the extracellular space is altered, which causes an increased concentration and range of action of the excitatory amino acid in the extracellular space. This leads to a reduction of synaptic efficacy at excitatory and inhibitory inputs through the activation of presynaptic metabotropic glutamate receptors. By contrast, the action of glio transmitters released from astrocytes and acting on adjacent magnocellular neurons is limited during such anatomical remodeling. This includes glia derived ATP mediating potentiation of glutamatergic transmission, a process compromised by the neuronal-glial reorganization.Together, these studies on hypothalamic magnocellular nuclei provide new insights on the contribution of glial cells on neuronal activity.     

Lacepède’s Syncretic Contribution to the Debates on Natural History in France Around 1800

Lacepède was a key figure in the French intellectual world from the Old Regime to the Restoration, sinc e he was not only a scientist, but also a musician, a writer, and a politician. His brilliant career is a good example of the progress of the social status of scientists in France around 1800. In the life sciences, he was considered the heir to Buffon and continued the latter’s Histoire naturelle, but he also borrowed ideas from anti-Buffonian (e.g. Linnaean) scientists. He broached many important subjects such as the nature of man, the classification of animals, the concept of species, and the history of the Earth. All these topics led to tensions in the French sciences, but Lacepède dealt with them in a consensual, indeed even ambiguous way. For example, he held transformist views, but his concept of evolution was far less precise and daring than Lamarck’s contemporaneous attempts. His somewhat confused eclecticism allowed him to be accepted by opposing camps of the French scientific community at that time and makes his case interesting for historians, since the opinions of such an opportunistic figure can illuminate the figure of the French intellectual better than more original works could do. In turn, Lacepède’s important social and scientific position gave his views a significant visibility. In this sense, his contributions probably exerted an influence, in particular with regard to the emergence of transformist theories.     

Analysis of the requirements for pilus biogenesis at the outer membrane usher and the function of the usher C-terminus

Uropathogenic strains of Escherichia coli assemble type 1 and P pili to colonize the bladder and kidney respectively. These pili are prototype structures assembled by the chaperone/usher secretion pathway. In this pathway, a periplasmic chaperone works together with an outer membrane (OM) usher to control the folding of pilus subunits, their assembly into a pilus fibre and secretion of the fibre to the cell surface. The usher serves as the assembly and secretion platform in the OM. The usher has distinct functional domains, with the N-terminus providing the initial targeting site for chaperone-subunit complexes and the C-terminus required for subsequent stages of pilus biogenesis. In this study, we investigated the molecular interactions occurring at the usher during pilus biogenesis and the function of the usher C-terminus. We provide genetic and biochemical evidence that the usher functions as a complex in the OM and that interaction of the pilus adhesin with the usher is critical to prime the usher for pilus biogenesis. Analysis of C-terminal truncation and substitution mutants of the P pilus usher PapC demonstrated that the C-terminus is required for proper binding of chaperone-subunit complexes to the usher and plays an important role in assembly of complete pili.     

Bile acids alter the subcellular localization of CNT2 (concentrative nucleoside cotransporter) and increase CNT2-related transport activity in liver parenchymal cells

PI3K (phosphoinositide 3-kinase) activity is involved in Ang (angiotensin) II-stimulated VSMC (vascular smooth muscle cell) growth and hypertrophy. In the present study, we demonstrate that the inhibition of PI3K in VSMCs by expression of a dominant-negative p85alpha mutant lacking the p110-binding domain (Deltap85), or by treatment of cells with LY294002, inhibited Ang II-stimulated PAI-1 (plasminogen activator inhibitor-1) mRNA expression. Using a GST (glutathione S-transferase) fusion protein containing the p85 N-terminal SH2 (Src homology 2) domain as 'bait' followed by MS/MS (tandem MS), we identified a 70 kDa fragment of the p70 PDGFR-beta (platelet-derived growth factor receptor-beta) as a signalling adapter that is phosphorylated and recruits the p85 subunit of PI3K after Ang II stimulation of AT1 (Ang II subtype 1) receptors on VSMCs. This fragment of the PDGFR-beta, which has a truncation of its extracellular domain, accounted for approx. 15% of the total PDGFR-beta detected in VSMCs with an antibody against its cytoplasmic domain. Stimulation of VSMCs with Ang II increased tyrosine-phosphorylation of p70 PDGFR-beta at Tyr751 and Tyr1021 and increased its binding to p85. PDGF also induced phosphorylation of p70 PDGFR-beta, a response inhibited by the PDGF tyrosine kinase selective inhibitor, AG1296. By contrast, Ang II-induced phosphorylation of the 70 kDa receptor was not affected by AG1296. Ang II-stimulated phosphorylation of the p70 PDGFR-beta was blocked by the AT1 receptor antagonist, candesartan (CV 11974) and was partially inhibited by PP2 {4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine}, an Src family kinase inhibitor. Our result suggests that the p70 PDGFR-beta functions as an adapter that recruits PI3K to the membrane upon AT1 receptor stimulation.     

A solar-powered transmitting video camera for monitoring cliff-nesting raptors

ABSTRACT.   We designed a system of solar-powered video cameras that transmitted images via telemetry to a monitor. This system allowed us to study the breeding behavior of the Bearded Vulture ( Gypaetus barbatus ) in the Pyrenees (northeastern Spain). From 2000 to 2004, 12 nests in seven territories were equipped with video cameras. To avoid disturbing the birds, equipment was installed 3–8 weeks before egg-laying. The acceptance rate was 75%. No decline in productivity was observed for nests monitored with video cameras compared to control nests. The cameras enabled us to document egg-laying, hatching asynchrony, the nestlings' diet, and the parents' breeding behavior from distances of 2–3 km, although technical problems temporarily interrupted the transmission of images. Video cameras can be used successfully to study the Bearded Vultures, and probably other cliff-nesting raptors, without reducing productivity.     

Crystal structure of Bacillus subtilis TrmB, the tRNA (m7G46) methyltransferase

The structure of Bacillus subtilis TrmB (BsTrmB), the tRNA (m7G46) methyltransferase, was determined at a resolution of 2.1 A. This is the first structure of a member of the TrmB family to be determined by X-ray crystallography. It reveals a unique variant of the Rossmann-fold methyltransferase (RFM) structure, with the N-terminal helix folded on the opposite site of the catalytic domain. The architecture of the active site and a computational docking model of BsTrmB in complex with the methyl group donor S-adenosyl-L-methionine and the tRNA substrate provide an explanation for results from mutagenesis studies of an orthologous enzyme from Escherichia coli (EcTrmB). However, unlike EcTrmB, BsTrmB is shown here to be dimeric both in the crystal and in solution. The dimer interface has a hydrophobic core and buries a potassium ion and five water molecules. The evolutionary analysis of the putative interface residues in the TrmB family suggests that homodimerization may be a specific feature of TrmBs from Bacilli, which may represent an early stage of evolution to an obligatory dimer.