Arabidopsis thaliana CENTRORADIALIS homologue (ATC) acts systemically to inhibit floral initiation in Arabidopsis

Floral initiation is orchestrated by systemic floral activators and inhibitors. This remote‐control system may integrate environmental cues to modulate floral initiation. Recently, FLOWERING LOCUS T (FT) was found to be a florigen. However, the identity of systemic floral inhibitor or anti‐florigen remains to be elucidated. Here we show that Arabidopsis thaliana CENTRORADIALIS homologue (ATC), an Arabidopsis FT homologue, may act in a non‐cell autonomous manner to inhibit floral initiation. Analysis of the ATC null mutant revealed that ATC is a short‐day‐induced floral inhibitor. Cell type‐specific expression showed that companion cells and apex that express ATC are sufficient to inhibit floral initiation. Histochemical analysis showed that the promoter activity of ATC was mainly found in vasculature but under the detection limit in apex, a finding that suggests that ATC may move from the vasculature to the apex to influence flowering. Consistent with this notion, Arabidopsis seedling grafting experiments demonstrated that ATC moved over a long distance and that floral inhibition by ATC is graft transmissible. ATC probably antagonizes FT activity, because both ATC and FT interact with FD and affect the same downstream meristem identity genes APETALA1, in an opposite manner. Thus, photoperiodic variations may trigger functionally opposite FT homologues to systemically influence floral initiation.     

A Plasmodium falciparum copper-binding membrane protein with copper transport motifs

Formerly known as a hypoendemic malaria country, the Republic of Djibouti declared the goal of pre-eliminating malaria in 2006. The aim of the present study was to evaluate the prevalence of Plasmodium falciparum, Plasmodium vivax and mixed infections in the Djiboutian population by using serological tools and to identify potential determinants of the disease and hotspots of malaria transmission within the country. The prevalence of P. falciparum and P. vivax within the districts of the capital city and the rest of the Republic of Djibouti were assessed using 13 and 2 serological markers, respectively. The relationship between the immune humeral response to P. falciparum and P. vivax and variables such as age, gender, wealth status, urbanism, educational level, distance to rivers/lakes, living area, having fever in the last month, and staying in a malaria-endemic country more than one year was estimated and analysed by questionnaires administered to 1910 Djiboutians. Multivariate ordinal logistic regression models of the immune humeral response were obtained for P. falciparum and P. vivax. The P. falciparum and P. vivax seroprevalence rates were 31.5%, CI95% [29.4-33.7] and 17.5%, CI95% [15.8-19.3], respectively. Protective effects against P. falciparum and P. vivax were female gender, educational level, and never having visited a malaria-endemic area for more than one year. For P. falciparum only, a protective effect was observed for not having a fever in the last month, living more than 1.5 km away from lakes and rivers, and younger ages. This is the first study that assessed the seroprevalence of P. vivax in the Republic of Djibouti. It is necessary to improve knowledge of this pathogen in order to create an effective elimination programme. As supported by recent observations on the subject, the Republic of Djibouti has probably demonstrated a real decrease in the transmission of P. falciparum in the past seven years, which should encourage authorities to improve efforts toward elimination.     

Fungal virulence studies come of age

Sophisticated molecular biological research has revealed many virulence attributes in at least four pathogenic fungi, but the future study of fungal virulence requires investigators to distinguish between molecules that directly interact with the host, molecules that regulate these, and molecules that are always required for fungal growth and survival, independent of the host.     

Cellular invasion by Staphylococcus aureus involves a fibronectin bridge between the bacterial fibronectin-binding MSCRAMMs and host cell beta1 integrins

Although Staphylococcus aureus is primarily considered an extracellular pathogen, recent evidence suggests that this bacterium can invade a variety of nonprofessional phagocytic cells. Here we investigate the early stages of cellular invasion by S. aureus and determine the bacterial and host components that are required for this process. S. aureus expresses two cell surface-associated fibronectin (FN)-binding proteins (FnbpA and FnbpB) that mediate the interaction of the bacteria with both soluble and solid-phase FN in vitro. Using a mutant of S. aureus that lacks the expression of both Fnbps, we show that the expression of either protein is necessary for efficient uptake by the mouse fibroblast line GD25beta1A. Invasion could be inhibited by soluble recombinant proteins encompassing either the FN-binding D repeat region or the A region (and B repeats) of FnbpA, suggesting that the activities of both regions are important in this process. We demonstrate that FN is also required for invasion of this cell line. In the presence of FN-depleted fetal bovine serum, the invasion level was reduced by approximately 40% compared to in the presence of whole fetal bovine serum. Invasion could be further reduced by the addition of anti-mouse FN antibodies to the assay. Finally, we utilize a mutant mouse fibroblast line, which lacks beta1 integrin expression, to demonstrate that host cell beta1 integrins are necessary for efficient cellular invasion. The level of invasion of the mutant cell line GD25 was reduced by approximately 97% compared to the beta1-expressing complemented cell line GD25beta1A. In addition, invasion of the GD25beta1A cell line could be inhibited by an RGD-containing peptide, further implicating a role for integrins in this process. Based on these observations, we put forward a model of S. aureus invasion in which host FN forms a bridge between the bacterial Fnbps and host cell beta1 integrins, leading to bacterial uptake.     

Clarithromycin resistance in Helicobacter pylori strains isolated from French children: prevalence of the different mutations and coexistence of clones harboring two different mutations in the same biopsy

BACKGROUND: The aim of our study was to assess the different mutations involved in clarithromycin-resistant Helicobacter pylori strains isolated from French children and their temporal trends. METHODS: The point mutations of H. pylori were detected by PCR followed by RFLP technique in 50 clarithromycin-resistant strains collected between 1993 and 2004 in France. RESULTS: Clarithromycin resistance was observed in 23% (50/217) of H. pylori isolates. Two mutations A2143G and A2142G in the 23S rRNA genes of H. pylori were detected. The former was found in 45/50 (90%) of isolates. The rate of resistance increased with time from 18.6% in the period 1993-1996 to 41.6% in 2001-2004. No significant difference was observed in the distribution of mutations during the same periods. No correlation was found between any mutation and age, sex, and ethnic origin of children. Furthermore, no significant differences in minimal inhibitory concentrations level were observed according to the different point mutations. In all cases, only one point mutation was present, except in two cases where two different mutations were found in two different clones from the same biopsy. CONCLUSION: The mutation A2143G is predominant in clarithromycin-resistant H. pylori strains isolated from children in France. We report for the first time the presence of two clarithromycin-resistant clones harboring two different mutations of the 23S rRNA genes present in the same biopsy specimen and genotypically identical as demonstrated by RAPD fingerprinting.     

Integrating sequence and structural biology with DAS

Background  

The Distributed Annotation System (DAS) is a network protocol for exchanging biological data. It is frequently used to share annotations of genomes and protein sequence.     

Glycosylation sites and site-specific glycosylation in human Tamm- Horsfall glycoprotein

The N-glycosylation sites of human Tamm-Horsfall glycoprotein from one healthy male donor have been characterized, based on an approach using endoproteinase Glu-C (V-8 protease, Staphylococcus aureus ) digestion and a combination of chromatographic techniques, automated Edman sequencing, and fast atom bombardment mass spectrometry. Seven out of the eight potential N-glycosylation sites, namely, Asn52, Asn56, Asn208, Asn251, Asn298, Asn372, and Asn489, turned out to be glycosylated, and the potential glycosylation site at Asn14, being close to the N-terminus, is not used. The carbohydrate microheterogeneity on three of the glycosylation sites was studied in more detail by high-pH anion-exchange chromatographic profiling and 500 MHz1H-NMR spectroscopy. Glycosylation site Asn489 contains mainly di- and tri-charged oligosaccharides which comprise, among others, the GalNAc4 S (beta1-4)GlcNAc terminal sequence. Only glycosylation site Asn251 bears oligomannose-type carbohydrate chains ranging from Man5GlcNAc2to Man8GlcNAc2, in addition to a small amount of complex- type structures. Profiling of the carbohydrate moieties of Asn208 indicates a large heterogeneity, similar to that established for native human Tamm-Horsfall glycoprotein, namely, multiply charged complex-type carbohydrate structures, terminated by sulfate groups, sialic acid residues, and/or the Sda-determinant.      

Reduction of apoptosis in the amygdala by an A2A adenosine receptor agonist following myocardial infarction

It has been observed that a cytokine synthesis inhibitor, pentoxifylline, prevents the apoptotic processes taking place in the amygdala following myocardial infarction. However, it is unknown if the cardioprotective effect of A_2A adenosine receptor agonist, CGS21680, which reduces cytokine synthesis, would lead to such amygdala apoptosis regression. Thus, this study was designed to investigate whether cardioprotective A_2A adenosine receptor activation reduces apoptosis in the amygdala following myocardial infarction. Anesthetized rats were subjected to left anterior descending coronary artery occlusion for 40 min, followed by 72 h of reperfusion. The A_2A agonist CGS21680 (0.2 μg/kg/min i.v.) was administered continuously for 120 min, starting (1) five minutes prior to instituting reperfusion (Early) or (2) five minutes after the beginning of reperfusion (Late). After reperfusion, myocardial infarct size was determined and the amygdala was dissected from the brain. Infarct size was reduced significantly in the Early compared to the Control group (34.6 ± 1.8% and 52.3 ± 2.8% respectively; p < 0.05), with no difference com-pared to the Late group (40.1 ± 6.1%). Apoptosis regressi-on was documented in the amygdala of the Early group by an enhanced phosphatidylinositol 3-kinase-Akt pathway activation and Bcl-2 expression concurrently to a caspase-3 activation limitation and reduction in TUNEL-positive cells staining. On the other hand, amygdala TUNEL-positive cell numbers were not reduced in the Late group. Moreover, TNFα was significantly reduced in the amygdala of the Early group compared to the Control and Late groups. These results indicate that A_2A adenosine receptor stimulation is associated with apoptosis regression in the amygdala following myocardial infarction. This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC).     

pH and monovalent cations regulate cytosolic free Ca(2+) in E. coli

The results here show for the first time that pH and monovalent cations can regulate cytosolic free Ca(2+) in E. coli through Ca(2+) influx and efflux, monitored using aequorin. At pH 7.5 the resting cytosolic free Ca(2+) was 0.2-0.5 microM. In the presence of external Ca(2+) (1 mM) at alkaline pH this rose to 4 microM, being reduced to 0.9 microM at acid pH. Removal of external Ca(2+) caused an immediate decrease in cytosolic free Ca(2+) at 50-100 nM s(-1). Efflux rates were the same at pH 5.5, 7.5 and 9.5. Thus, ChaA, a putative Ca(2+)/H(+)exchanger, appeared not to be a major Ca(2+)-efflux pathway. In the absence of added Na(+), but with 1 mM external Ca(2+), cytosolic free Ca(2+) rose to approximately 10 microM. The addition of Na(+)(half maximum 60 mM) largely blocked this increase and immediately stimulated Ca(2+) efflux. However, this effect was not specific, since K(+) also stimulated efflux. In contrast, an increase in osmotic pressure by addition of sucrose did not significantly stimulate Ca(2+) efflux. The results were consistent with H(+) and monovalent cations competing with Ca(2+) for a non-selective ion influx channel. Ca(2+) entry and efflux in chaA and yrbG knockouts were not significantly different from wild type, confirming that neither ChaA nor YrbG appear to play a major role in regulating cytosolic Ca(2+) in Escherichia coli. The number of Ca(2+) ions calculated to move per cell per second ranged from <1 to 100, depending on conditions. Yet a single eukaryote Ca(2+) channel, conductance 100 pS, should conduct >6 million ions per second. This raises fundamental questions about the nature and regulation of Ca(2+) transport in bacteria, and other small living systems such as mitochondria, requiring a new mathematical approach to describe such ion movements. The results have important significance in the adaptation of E. coli to different ionic environments such as the gut, fresh water and in sea water near sewage effluents.