Epizootiological studies of Amblyospora camposi (Microsporidia: Amblyosporidae) in Culex renatoi (Diptera: Culicidae) and Paracyclops fimbriatus fimbriatus (Copepoda: Cyclopidae) in a bromeliad habitat

The epizootiology of Amblyospora camposi was studied in a natural population of Culex renatoi, a bromeliad-inhabiting mosquito, and its intermediate host, Paracyclops fimbriatus fimbriatus, over a 2-year period. Twenty Eryngium cabrerae plants were sampled monthly from January 2003 to January 2005 and the prevalence of A. camposi in P.f. fimbriatus and Cx. renatoi populations was determined. The monthly prevalence rates of meiospore infections in Cx. renatoi larvae never exceeded 5.5% and was detected in 50% of the monthly samples. Meiospores were available in plants over the course of the study at a mean concentration of 2 x 10(4) meiospores/ml. Within each plant the parasite was maintained by horizontal transmission. P.f. fimbriatus with vegetative stages and mature spores were found regularly in bromeliads suggesting efficient meiospore infectivity to field copepod populations. The mean concentration of spores from copepods found in plants was 8 x 10(2) spores/ml. Infections in copepods were detected in 54% of the monthly samples with a prevalence rate ranging from 0.55 to 17.4% and an overall average of 5.1%. Vegetative stages in fourth instar mosquito larvae (probably derived from the horizontal pathway via spores formed in copepods) were detected in 12.5% of the monthly samples with an overall prevalence rate of 1.1%. Infections in female and male adults were detected in 20.8% of the monthly samples with an overall average of 4.1% and 6.8%, respectively.     

Melatonin prevents glutamate-induced oxytosis in the HT22 mouse hippocampal cell line through an antioxidant effect specifically targeting mitochondria

The pineal hormone melatonin has neuroprotective effects in a large number of models of neurodegeneration. Melatonin crosses the blood-brain barrier, shows a decrease in its nocturnal peaks in blood with age that has been associated with the development of neurodegenerative disorders, and has been shown to be harmless at high concentrations. These properties make melatonin a potential therapeutic agent against neurodegenerative disorders but the pathways involved in such neuroprotective effects remain unknown. In the present report we study the intracellular pathways implicated in the complete neuroprotection provided by melatonin against glutamate-induced oxytosis in the HT22 mouse hippocampal cell line. Our results strongly suggest that melatonin prevents oxytosis through a direct antioxidant effect specifically targeted at the mitochondria. Firstly, none of the described transducers of melatonin signalling seems to be implicated in the neuroprotection provided by this indole. Secondly, melatonin does not prevent cytosolic GSH depletion-dependent increase in reactive oxygen species (ROS), but it totally prevents mitochondrial ROS production despite the fact that the latter is much higher than the former. And finally, there is a high correlation between the concentration at which melatonin and closely related indoles exert a direct antioxidant effect in vitro and a neuroprotective effect against glutamate-induced oxytosis.     

Increased neutralization sensitivity of recently emerged CXCR4-using human immunodeficiency virus type 1 strains compared to coexisting CCR5-using variants from the same patient

CXCR4-using (X4) human immunodeficiency virus type 1 (HIV-1) variants evolve from CCR5-using (R5) variants relatively late in the natural course of infection in 50% of HIV-1 subtype B-infected individuals and subsequently coexist with R5 HIV-1 variants. This relatively late appearance of X4 HIV-1 variants is poorly understood. Here we tested the neutralization sensitivity for soluble CD4 (sCD4) and the broadly neutralizing antibodies IgG1b12, 2F5, 4E10, and 2G12 of multiple coexisting clonal R5 and (R5)X4 (combined term for monotropic X4 and dualtropic R5X4 viruses) HIV-1 variants that were obtained at two time points after the first appearance of X4 variants in five participants of the Amsterdam Cohort Studies on HIV-1 infection and AIDS. Recently emerged (R5)X4 viruses were significantly more sensitive to neutralization by the CD4-binding-site-directed agents sCD4 and IgG1b12 than their coexisting R5 viruses. This difference was less pronounced at the later time point. Early (R5)X4 variants from two out of four patients were also highly sensitive to neutralization by autologous serum (50% inhibition at serum dilutions of >200). Late (R5)X4 viruses from these two patients were neutralized at lower serum dilutions, which suggested escape of X4 variants from humoral immunity. Autologous neutralization of coexisting R5 and (R5)X4 variants was not observed in the other patients. In conclusion, the increased neutralization sensitivity of HIV-1 variants during the transition from CCR5 usage to CXCR4 usage may imply an inhibitory role for humoral immunity in HIV-1 phenotype evolution in some patients, thus potentially contributing to the late emergence of X4 variants.     

The calcium-binding C-terminal domain of Escherichia coli alpha-hemolysin is a major determinant in the surface-active properties of the protein

alpha-Hemolysin (HlyA) from Escherichia coli is a protein toxin (1024 amino acids) that targets eukaryotic cell membranes, causing loss of the permeability barrier. HlyA consists of two main regions, an N-terminal domain rich in amphipathic helices, and a C-terminal Ca(2+)-binding domain containing a Gly- and Asp-rich nonapeptide repeated in tandem 11-17 times. The latter is called the RTX domain and gives its name to the RTX protein family. It had been commonly assumed that membrane interaction occurred mainly if not exclusively through the amphipathic helix domain. However, we have cloned and expressed the C-terminal region of HlyA, containing the RTX domain plus a few stabilizing sequences, and found that it is a potent surface-active molecule. The isolated domain binds Ca(2+) with about the same affinity (apparent K(0.5) approximately 150 microM) as the parent protein HlyA, and Ca(2+) binding induces in turn a more compact folding with an increased proportion of beta-sheet structure. Both with and without Ca(2+) the C-terminal region of HlyA can interact with lipid monolayers spread at an air-water interface. However, the C-terminal domain by itself is devoid of membrane lytic properties. The present results can be interpreted in the light of our previous studies that involved in receptor binding a peptide in the C-terminal region of HlyA. We had also shown experimentally the distinction between reversible membrane adsorption and irreversible lytic insertion of the toxin. In this context, the present data allow us to propose that both major domains of HlyA are directly involved in membrane-toxin interaction, the nonapeptide repeat, calcium-binding RTX domain being responsible for the early stages of HlyA docking to the target membrane.     

Classical Xenopus laevis progesterone receptor associates to the plasma membrane through its ligand-binding domain

During the last decade, considerable evidence is accumulating that supports the view that the classic progesterone receptor (xPR-1) is mediating Xenopus laevis oocyte maturation through a non-genomic mechanism. Overexpression and depletion of oocyte xPR-1 have been shown to accelerate and to block progesterone-induced oocyte maturation, respectively. In addition, rapid inhibition of plasma membrane adenylyl cyclase (AC) by the steroid hormone, supports the idea that xPR-1 should be localized at the oocyte plasma membrane. To test this hypothesis, we transiently transfected xPR-1 cDNA into Cos-7 cells and analyzed its subcellular distribution. Through Western blot and immunofluorescence analysis, we were able to detect xPR-1 associated to the plasma membrane of transfected Cos-7 cells. Additionally, using Progesterone-BSA-FITC, we identified specific progesterone-binding sites at the cell surface of xPR-1 expressing cells. Finally, we found that the receptor ligand-binding domain displayed membrane localization, in contrast to the N-terminal domain, which expressed in similar levels, remained cytosolic. Overall, these results indicate that a fraction of xPR-1 expressed in Cos-7 cells, associates to the plasma membrane through its LBD.     

Effects of an African weaver ant, Oecophylla longinoda, in controlling mango fruit flies (Diptera: Tephritidae) in Benin

Six mango, Mangifera indica L., plantations around Parakou, northern Benin, were sampled at 2-wk intervals for fruit fly damage from early April to late May in 2005. Mean damage ranged from 1 to 24% with a weaver ant, Oecophylla longinoda (Latreille), being either abundant or absent. The fruit fly complex is made up of Ceratitis spp. and Bactrocera invadens Drew et al., a new invasive species in West Africa. In 2006, Ceratitis spp. peaked twice in the late dry season in early April and early May, whereas B. invadens populations quickly increased at the onset of the rains, from mid-May onward. Exclusion experiments conducted in 2006 with 'Eldon', 'Kent', and 'Gouverneur' confirmed that at high ant abundance levels, Oecophylla significantly reduced fruit fly infestation. Although fruit fly control methods are still at an experimental stage in this part of the world, farmers who tolerated weaver ants in their orchard were rewarded by significantly better fruit quality. Conservation biological control with predatory ants such as Oecophylla in high-value tree crops has great potential for African and Asian farmers. Implications for international research for development at the Consultative Group on International Agricultural Research level are discussed.     

Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper

Tomato and pepper are two Solanaceous fruit crops that display an enormous diversity in fruit morphology. In this review, we will present an overview of the history of tomato and pepper and discuss key plant traits that were specifically selected during domestication of the two species. The traits discussed are fruit weight, shape, colour, ripening, pungency and plant architecture. We will review these characteristics as well as the genetic loci or genes that control these features, questioning whether mutations at orthologous loci occurred independently in these two species or whether unique plant and fruit features resulted in selection at different genes.