Large-scale use of mosquito larval source management for malaria control in Africa: a cost analysis

Background

At present, large-scale use of two malaria vector control methods, long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) is being scaled up in Africa with substantial funding from donors. A third vector control method, larval source management (LSM), has been historically very successful and is today widely used for mosquito control globally, except in Africa. With increasing risk of insecticide resistance and a shift to more exophilic vectors, LSM is now under re-evaluation for use against afro-tropical vector species. Here the costs of this intervention were evaluated.

Methods

The 'ingredients approach' was used to estimate the economic and financial costs per person protected per year (pppy) for large-scale LSM using microbial larvicides in three ecologically diverse settings: (1) the coastal metropolitan area of Dar es Salaam in Tanzania, (2) a highly populated Kenyan highland area (Vihiga District), and (3) a lakeside setting in rural western Kenya (Mbita Division). Two scenarios were examined to investigate the cost implications of using alternative product formulations. Sensitivity analyses on product prices were carried out.

Results

The results show that for programmes using the same granular formulation larviciding costs the least pppy in Dar es Salaam (US$0.94), approximately 60% more in Vihiga District (US$1.50) and the most in Mbita Division (US$2.50). However, these costs are reduced substantially if an alternative water-dispensable formulation is used; in Vihiga, this would reduce costs to US$0.79 and, in Mbita Division, to US$1.94. Larvicide and staff salary costs each accounted for approximately a third of the total economic costs per year. The cost pppy depends mainly on: (1) the type of formulation required for treating different aquatic habitats, (2) the human population density relative to the density of aquatic habitats and (3) the potential to target the intervention in space and/or time.

Conclusion

Costs for LSM compare favourably with costs for IRS and LLINs, especially in areas with moderate and focal malaria transmission where mosquito larval habitats are accessible and well defined. LSM presents an attractive tool to be integrated in ongoing malaria control effort in such settings. Further data on the epidemiological health impact of larviciding is required to establish cost effectiveness.     

Structure of cytochrome c6A, a novel dithio-cytochrome of Arabidopsis thaliana, and its reactivity with plastocyanin: implications for function

Cytochrome c6A is a unique dithio-cytochrome present in land plants and some green algae. Its sequence and occurrence in the thylakoid lumen suggest that it is derived from cytochrome c6, which functions in photosynthetic electron transfer between the cytochrome b6f complex and photosystem I. Its known properties, however, and a strong indication that the disulfide group is not purely structural, indicate that it has a different, unidentified function. To help in the elucidation of this function the crystal structure of cytochrome c6A from Arabidopsis thaliana has been determined in the two redox states of the heme group, at resolutions of 1.2 A (ferric) and 1.4 A (ferrous). These two structures were virtually identical, leading to the functionally important conclusion that the heme and disulfide groups do not communicate by conformational change. They also show, however, that electron transfer between the reduced disulfide and the heme is feasible. We therefore suggest that the role of cytochrome c6A is to use its disulfide group to oxidize dithiol/disulfide groups of other proteins of the thylakoid lumen, followed by internal electron transfer from the dithiol to the heme, and re-oxidation of the heme by another thylakoid oxidant. Consistent with this model, we found a rapid electron transfer between ferro-cytochrome c6A and plastocyanin, with a second-order rate constant, k2=1.2 x 10(7) M(-1) s(-1).     

Why do asthmatic subjects respond so strongly to inhaled adenosine?

Bronchospasm induced by adenosine is blocked by representatives of all the major classes of drugs used in the treatment of asthma. Understanding the mechanism of this bronchospasm may help understand the way these drugs work. Clinical studies have suggested involvement of neural pathways, mast-like cells and mediators such as histamine, serotonin and lipoxygenase products. There is a strong link between responsiveness to adenosine and eosinophilia. In different animal models A1, A2b and A3 adenosine receptor subclasses have all been implicated in inducing bronchospasm. whilst occupation of the A2a receptor generally has no, or the opposite effect. At least two different mechanisms, both involving neural pathways, exist. One, involving the adenosine A1 receptor, functions in mast cell depleted animals; the other requires interaction with a population of mast-like cells activated over A2b or A3 receptors. Not only histamine but also serotonin and lipoxygenase products released from the mast-like cells are potential mediators. In animal models good reactivity to adenosine receptor agonists is generally only found when the animals are first sensitized and exposed to allergen in ways likely to induce an allergic inflammation. An exception is the BDE rat, which reacts to adenosine receptor agonists such as APNEA or NECA even without allergen exposure. This rat strain does however show evidence of spontaneous eosinophilic inflammation in the lung even without immunization. As mast cells both release adenosine and respond to adenosine, adenosine provides a non-specific method of amplifying specific signals resulting from IgE/antigen interaction. This mechanism may not only have a pathological significance in asthma; it may be part of a normal bodily defense response that in asthmatic subjects is inappropriately activated.     

The effects of intracellular calcium depletion on insulin signaling in 3T3-L1 adipocytes

We have examined the requirement for intracellular calcium (Ca(2+)) in insulin signal transduction in 3T3-L1 adipocytes. Using the Ca(2+) chelator 1,2- bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, sodium (BAPTA-AM), we find both augmentation and inhibition of insulin signaling phenomena. Pretreatment of cells with 50 microM BAPTA-AM did not affect tyrosine phosphorylation of insulin receptor substrate (IRS)1/2 or insulin receptor (IR)beta. The decreased mobility of IRS1 normally observed after chronic stimulation with insulin, due to serine phosphorylation, was completely eliminated by Ca(2+) chelation. Correlating with decreased insulin-induced serine phosphorylation of IRS1, phosphotyrosine-mediated protein-protein interactions involving p85, IRS1, IRbeta, and phosphotyrosine-specific antibody were greatly enhanced by pretreatment of cells with BAPTA-AM. As a result, insulin-mediated, phosphotyrosine-associated PI3K activity was also enhanced. BAPTA-AM pretreatment inhibited other insulin-induced phosphorylation events including phosphorylation of Akt, MAPK (ERK1 and 2) and p70 S6K. Phosphorylation of Akt on threonine-308 was more sensitive to Ca(2+) depletion than phosphorylation of Akt on serine-473 at the same insulin dose (10 nM). In vitro 3'-phosphatidylinositol-dependent kinase 1 activity was unaffected by BAPTA-AM. Insulin-stimulated insulin-responsive glucose transporter isoform translocation and glucose uptake were both inhibited by calcium depletion. In summary, these data demonstrate a positive role for intracellular Ca(2+) in distal insulin signaling events, including initiation/maintenance of Akt phosphorylation, insulin-responsive glucose transporter isoform translocation, and glucose transport. A negative role for Ca(2+) is also indicated in proximal insulin signaling steps, in that, depletion of intracellular Ca(2+) blocks IRS1 serine/threonine phosphorylation and enhances insulin-stimulated protein-protein interaction and PI3K activity.     

Functional studies of signaling pathways in peri-implantation development of the mouse embryo by RNAi

Background

Studies of gene function in the mouse have relied mainly on gene targeting via homologous recombination. However, this approach is difficult to apply in specific windows of time, and to simultaneously knock-down multiple genes. Here we report an efficient method for dsRNA-mediated gene silencing in late cleavage-stage mouse embryos that permits examination of phenotypes at post-implantation stages.

Results

We show that introduction of Bmp4 dsRNA into intact blastocysts by electroporation recapitulates the genetic Bmp4 null phenotype at gastrulation. It also reveals a novel role for Bmp4 in the regulation the anterior visceral endoderm specific gene expression and its positioning. We also show that RNAi can be used to simultaneously target several genes. When applied to the three murine isoforms of Dishevelled, it leads to earlier defects than previously observed in double knock-outs. These include severe delays in post-implantation development and defects in the anterior midline and neural folds at headfold stages.

Conclusion

Our results indicate that the BMP4 signalling pathway contributes to the development of the anterior visceral endoderm, and reveal an early functional redundancy between the products of the murine Dishevelled genes. The proposed approach constitutes a powerful tool to screen the functions of genes that govern the development of the mouse embryo.     

Crystal structure of the C‐terminal domain of the Salmonella type III secretion system export apparatus protein InvA

InvA is a prominent inner‐membrane component of the Salmonella type III secretion system (T3SS) apparatus, which is responsible for regulating virulence protein export in pathogenic bacteria. InvA is made up of an N‐terminal integral membrane domain and a C‐terminal cytoplasmic domain that is proposed to form part of a docking platform for the soluble export apparatus proteins notably the T3SS ATPase InvC. Here, we report the novel crystal structure of the C‐terminal domain of Salmonella InvA which shows a compact structure composed of four subdomains. The overall structure is unique although the first and second subdomains exhibit structural similarity to the peripheral stalk of the A/V‐type ATPase and a ring building motif found in other T3SS proteins respectively.     

Germ band retraction as a landmark in glucose metabolism during <Emphasis Type="Italic">Aedes aegypti</Emphasis> embryogenesis

Background  

The mosquito A. aegypti is vector of dengue and other viruses. New methods of vector control are needed and can be achieved by a better understanding of the life cycle of this insect. Embryogenesis is a part of A. aegypty life cycle that is poorly understood. In insects in general and in mosquitoes in particular energetic metabolism is well studied during oogenesis, when the oocyte exhibits fast growth, accumulating carbohydrates, lipids and proteins that will meet the regulatory and metabolic needs of the developing embryo. On the other hand, events related with energetic metabolism during A. aegypti embryogenesis are unknown.     

Interaction of yeast iso-1-cytochrome c with cytochrome c peroxidase investigated by [15N, 1H] heteronuclear NMR spectroscopy

The interaction of yeast iso-1-cytochrome c with its physiological redox partner cytochrome c peroxidase has been investigated using heteronuclear NMR techniques. Chemical shift perturbations for both 15N and 1H nuclei arising from the interaction of isotopically enriched 15N cytochrome c with cytochrome c peroxidase have been observed. For the diamagnetic, ferrous cytochrome c, 34 amides are affected by binding, corresponding to residues at the front face of the protein and in agreement with the interface observed in the 1:1 crystal structure of the complex. In contrast, for the paramagnetic, ferric protein, 56 amides are affected, corresponding to residues both at the front and toward the rear of the protein. In addition, the chemical shift perturbations were larger for the ferric protein. Using experimentally observed pseudocontact shifts the magnetic susceptibility tensor of yeast iso-1-cytochrome c in both the free and bound forms has been calculated with HN nuclei as inputs. In contrast to an earlier study, the results indicate that there is no change in the geometry of the magnetic axes for cytochrome c upon binding to cytochrome c peroxidase. This leads us to conclude that the additional effects observed for the ferric protein arise either from a difference in binding mode or from the more flexible overall structure causing a transmittance effect upon binding.     

Pollen maturation: Where ubiquitin is not required?

A recent paper⁽¹⁾ describing the stage-specific loss of ubiquitin (UBQ) and ubiquitinated proteins (UBQ-Ps) during pollen development has raised some interesting questions regarding our understanding of the regulation of protein turnover during cellular differentiation and the specialized development of the pollen grain. The authors, Callis and Bedinger⁽¹⁾, describe experiments in which the profiles of free and protein-conjugated ubiquitin were examined during pollen development. UBQ and UBQ-Ps were immunologically detected in extracts of microspores and maturing pollen of maize at six developmental stages. Their results remarkably demonstrate that UBQ and UBQ-Ps decline to barely detectable levels during the final stages of pollen development.