Biomorphometric characteristics of different types of sensilla detected on the antenna of Helicoverpa armigera by scanning electron microscopy

A morphometric study on H. armigera antenna showed four styles of sensilla, i.e., styloconica, chaetica, coeloconica, and trichodea, and their numbers were estimated. Sensilla trichodea detect inter and intraspecific communication signals and was the most numerous. They were divided into three types: type I, the longest, with a length of 34.04 ± 3.16 μm and about 2.16 to 2.42 μm in diameter at its base; 2) type II, intermediate, with a length of 22.58 ± 0.77 μm and basal diameter of 1.8–2.52 μm; 3) type III, the shortest sensilla trichodea, with a length of 7.62 ± 0.4 μm and a range in diameter similar to that of type II. The length of the female sensilla trichodea was longer than that of the male. The total number of sensilla trichodea was estimated to be 7520 on the antenna of the female, and 6831 on the male antenna. The lengths of the sensilla trichodea type I and type III were significantly different on male (t = 4.6881, P = 0.0034) and female antenna (t = 18.9852, P = 0.0001). An estimation of the predicted surface area of the most numerous type I on sampled segments between the 12th and 20th segments from a female of H. armigera showed a surface area of 5 × 10³ μm² and a sensillar density of 38 sensilla/10³ μm². The fraction of sensilla-occupied surface area was 0.4 μm².     

Impact of changing drug treatment and malaria endemicity on the heritability of malaria phenotypes in a longitudinal family-based cohort study

Despite considerable success of genome wide association (GWA) studies in identifying causal variants for many human diseases, their success in unraveling the genetic basis to complex diseases has been more mitigated. Pathogen population structure may impact upon the infectious phenotype, especially with the intense short-term selective pressure that drug treatment exerts on pathogens. Rigorous analysis that accounts for repeated measures and disentangles the influence of genetic and environmental factors must be performed. Attempts should be made to consider whether pathogen diversity will impact upon host genetic responses to infection.We analyzed the heritability of two Plasmodium falciparum phenotypes, the number of clinical malaria episodes (PFA) and the proportion of these episodes positive for gametocytes (Pfgam), in a family-based cohort followed for 19 years, during which time there were four successive drug treatment regimes, with documented appearance of drug resistance. Repeated measures and variance components analyses were performed with fixed environmental, additive genetic, intra-individual and maternal effects for each drug period. Whilst there was a significant additive genetic effect underlying PFA during the first drug period of study, this was lost in subsequent periods. There was no additive genetic effect for Pfgam. The intra-individual effect increased significantly in the chloroquine period.The loss of an additive genetic effect following novel drug treatment may result in significant loss of power to detect genes in a GWA study. Prior genetic analysis must be a pre-requisite for more detailed GWA studies. The temporal changes in the individual genetic and the intra-individual estimates are consistent with those expected if there were specific host-parasite interactions. The complex basis to the human response to malaria parasite infection likely includes dominance/epistatic genetic effects encompassed within the intra-individual variance component. Evaluating their role in influencing the outcome of infection through host genotype by parasite genotype interactions warrants research effort.     

Identity by descent mapping of founder mutations in cancer using high-resolution tumor SNP data

Dense genotype data can be used to detect chromosome fragments inherited from a common ancestor in apparently unrelated individuals. A disease-causing mutation inherited from a common founder may thus be detected by searching for a common haplotype signature in a sample population of patients. We present here FounderTracker, a computational method for the genome-wide detection of founder mutations in cancer using dense tumor SNP profiles. Our method is based on two assumptions. First, the wild-type allele frequently undergoes loss of heterozygosity (LOH) in the tumors of germline mutation carriers. Second, the overlap between the ancestral chromosome fragments inherited from a common founder will define a minimal haplotype conserved in each patient carrying the founder mutation. Our approach thus relies on the detection of haplotypes with significant identity by descent (IBD) sharing within recurrent regions of LOH to highlight genomic loci likely to harbor a founder mutation. We validated this approach by analyzing two real cancer data sets in which we successfully identified founder mutations of well-characterized tumor suppressor genes. We then used simulated data to evaluate the ability of our method to detect IBD tracts as a function of their size and frequency. We show that FounderTracker can detect haplotypes of low prevalence with high power and specificity, significantly outperforming existing methods. FounderTracker is thus a powerful tool for discovering unknown founder mutations that may explain part of the "missing" heritability in cancer. This method is freely available and can be used online at the FounderTracker website.     

Mosquito survey in Mauritania: Detection of Rift Valley fever virus and dengue virus and the determination of feeding patterns

In Mauritania, several mosquito-borne viruses have been reported that can cause devastating diseases in animals and humans. However, monitoring data on their occurrence and local distribution are limited. Rift Valley fever virus (RVFV) is an arthropod-borne virus that causes major outbreaks throughout the African continent and the Arabian Peninsula. The first Rift Valley fever (RVF) epidemic in Mauritania occurred in 1987 and since then the country has been affected by recurrent outbreaks of the disease. To gain information on the occurrence of RVFV as well as other mosquito-borne viruses and their vectors in Mauritania, we collected and examined 4,950 mosquitoes, belonging to four genera and 14 species. The mosquitoes were captured during 2018 in the capital Nouakchott and in southern parts of Mauritania. Evidence of RVFV was found in a mosquito pool of female Anopheles pharoensis mosquitoes collected in December on a farm near the Senegal River. At that time, 37.5% of 16 tested Montbéliarde cattle on the farm showed RVFV-specific IgM antibodies. Additionally, we detected IgM antibodies in 10.7% of 28 indigenous cattle that had been sampled on the same farm one month earlier. To obtain information on potential RVFV reservoir hosts, blood meals of captured engorged mosquitoes were analyzed. The mosquitoes mainly fed on humans (urban areas) and cattle (rural areas), but also on small ruminants, donkeys, cats, dogs and straw-colored fruit bats. Results of this study demonstrate the circulation of RVFV in Mauritania and thus the need for further research to investigate the distribution of the virus and its vectors. Furthermore, factors that may contribute to its maintenance should be analyzed more closely. In addition, two mosquito pools containing Aedes aegypti and Culex quinquefasciatus mosquitoes showed evidence of dengue virus (DENV) 2 circulation in the city of Rosso. Further studies are therefore needed to also examine DENV circulation in Mauritania.     

The Bacillus thuringiensis Cry1Aa toxin: effects of trypsin and chymotrypsin site mutations on toxicity and stability

The objective of the present work was to create an active Cry1Aa toxin showing enhanced resistance to degradation by spruce budworm (Choristoneura fumiferana) midgut proteases by mutating potential chymotrypsin and trypsin sites. Fourteen Cry1Aa mutants were created in an Escherichia coli-Bacillus shuttle vector and expressed in a crystal minus Bacillus thuringiensis host. Using spruce budworm gut juice, commercial bovine trypsin and chymotrypsin we performed protease resistance assays with Cry1Aa wild type and mutant toxins. Although many mutants showed little or no change, several mutants showed a > 2-fold increase (R543S, R566G, and F570S) up to a > 4-fold increase in toxicity (F576S), in bioassay studies against C. fumiferana. The in vitro protease resistance assay results indicated a possible involvement of other gut juice components in toxin overdigestion.     

L’Observatoire hommes–milieux international Tessékéré (OHMi) : un outil de recherche pour étudier la complexité des écosystèmes arides du Sahel

In the Sahelian zone, the drought phenomenon, combined with anthropic factors (monoculture, bush fires, defect or deficit of manure, overgrazing, etc.), has seriously affected ecological great balances, involving a degradation of the natural resources as well as a fall in agricultural productions, pointing to a process of desertification. To face these challenges, in the course of the 8th ordinary session of the conference of the Heads of States of the African Union held in January 2007 in Addis Ababa (Ethiopia), 11 countries adopted the Panafrican project called the Green Great Wall (GGW). The total objective of the GGW is to contribute i) to the fight against the desert's advance, ii) to the development of the Saharan-Sahelian zones toward a durable management of the natural resources, and iii) to the fight against poverty. It deals with the construction of a set of zones of afforestation crossing the whole African continent in the long term (7000 km of which are in the west). Even if some decisions in the launching phase the GGW must be taken quickly, one cannot do without investment in interdisciplinary research. In particular, associating fundamental research and applied research will allow us to ensure the success in the medium and long term of such a large-scale reforestation project. Research segmented in compartmentalized knowledge fields needed to get adequate tools, among which OHMi Tessékéré, initiated by INNEE (Centre national de la recherche scientifique [CNRS]), in partnership with UCAD, constitutes an example. This suitable scientific tool, capable of action flexibility, of self-financing capacity, anchored in civil society, ready to implement a pragmatic and local interdisciplinarity founded currently on the concept of socio-ecological system (SES), is the one we chose to conduct our studies on the Ferlo arid ecosystems.     

An exhaustive, non-euclidean, non-parametric data mining tool for unraveling the complexity of biological systems--novel insights into malaria

Complex, high-dimensional data sets pose significant analytical challenges in the post-genomic era. Such data sets are not exclusive to genetic analyses and are also pertinent to epidemiology. There has been considerable effort to develop hypothesis-free data mining and machine learning methodologies. However, current methodologies lack exhaustivity and general applicability. Here we use a novel non-parametric, non-euclidean data mining tool, HyperCube®, to explore exhaustively a complex epidemiological malaria data set by searching for over density of events in m-dimensional space. Hotspots of over density correspond to strings of variables, rules, that determine, in this case, the occurrence of Plasmodium falciparum clinical malaria episodes. The data set contained 46,837 outcome events from 1,653 individuals and 34 explanatory variables. The best predictive rule contained 1,689 events from 148 individuals and was defined as: individuals present during 1992–2003, aged 1–5 years old, having hemoglobin AA, and having had previous Plasmodium malariae malaria parasite infection ≤10 times. These individuals had 3.71 times more P. falciparum clinical malaria episodes than the general population. We validated the rule in two different cohorts. We compared and contrasted the HyperCube® rule with the rules using variables identified by both traditional statistical methods and non-parametric regression tree methods. In addition, we tried all possible sub-stratified quantitative variables. No other model with equal or greater representativity gave a higher Relative Risk. Although three of the four variables in the rule were intuitive, the effect of number of P. malariae episodes was not. HyperCube® efficiently sub-stratified quantitative variables to optimize the rule and was able to identify interactions among the variables, tasks not easy to perform using standard data mining methods. Search of local over density in m-dimensional space, explained by easily interpretable rules, is thus seemingly ideal for generating hypotheses for large datasets to unravel the complexity inherent in biological systems.     

Diversity of Toxoplasma gondii strains shaped by commensal communities of small mammals

Commensal rodent species are key reservoirs for Toxoplasma gondii in the domestic environment. In rodents, different T. gondii strains show variable patterns of virulence according to host species. Toxoplasma gondii strains causing non-lethal chronic infections in local hosts will be more likely to persist in a given environment, but few studies have addressed the possible role of these interactions in shaping the T. gondii population structure. In addition, the absence of validated techniques for upstream detection of T. gondii chronic infection in wild rodents hinders exploration of this issue under natural conditions. In this study, we took advantage of an extensive survey of commensal small mammals in three coastal localities of Senegal, with a species assemblage constituted of both native African species and invasive species. We tested 828 individuals for T. gondii chronic infection using the modified agglutination test for antibody detection in serum samples and a quantitative PCR assay for detection of T. gondii DNA in brain samples. The infecting T. gondii strains were genotyped whenever possible by the analysis of 15 microsatellite markers. We found (i) a very poor concordance between molecular detection and serology in the invasive house mouse, (ii) significantly different levels of prevalence by species and (iii) the autochthonous T. gondii Africa 1 lineage strains, which are lethal for laboratory mice, only in the native African species of commensal small mammals. Overall, this study highlights the need to reconsider the use of MAT serology in natural populations of house mice and provides the first known data about T. gondii genetic diversity in invasive and native species of small mammals from Africa. In light of these results, we discuss the role of invasive and native species, with their variable adaptations to different T. gondii strains, in shaping the spatial structure of T. gondii genetic diversity in Africa.     

Contemporary variations of immune responsiveness during range expansion of two invasive rodents in Senegal

Biological invasions provide unique opportunities for studying life history trait changes over contemporary time scales. As spatial spread may be related to changes in parasite communities, several hypotheses (such as the evolution of increased competitive ability (EICA) or EICA‐refined hypotheses) suggest immune changes in invasive species along invasion gradients. Although native hosts may be subject to similar changes in parasite selection pressures, their immune responses have been rarely investigated in invasion contexts. In this study, we evaluated immune variations for invasive house mice Mus musculus domesticus, invasive black rats Rattus rattus and native rodents Mastomys erythroleucus and Mastomys natalensis along well‐characterised invasion gradients in Senegal. We focused on antibody‐mediated (natural antibodies and complement) and inflammatory (haptoglobin) responses. One invasion route was considered for each invasive species, and environmental conditions were recorded. Natural‐antibody mediated responses increased between sites of long‐established invasion and recently invaded sites only in house mice. Both invasive species exhibited higher inflammatory responses at the invasion front than in sites of long‐established invasion. The immune responses of native species did not change with the presence of invasive species. These patterns of immune variations do not support the EICA and EICA refined hypotheses, and they rather suggest a higher risk of exposure to parasites on the invasion front. Altogether, these results provide a first basis to further assess the role of immune changes in invasion success.     

Mutations in Domain I Interhelical Loops Affect the Rate of Pore Formation by the Bacillus thuringiensis Cry1Aa Toxin in Insect Midgut Brush Border Membrane Vesicles

Pore formation in the apical membrane of the midgut epithelial cells of susceptible insects constitutes a key step in the mode of action of Bacillus thuringiensis insecticidal toxins. In order to study the mechanism of toxin insertion into the membrane, at least one residue in each of the pore-forming-domain (domain I) interhelical loops of Cry1Aa was replaced individually by cysteine, an amino acid which is normally absent from the activated Cry1Aa toxin, using site-directed mutagenesis. The toxicity of most mutants to Manduca sexta neonate larvae was comparable to that of Cry1Aa. The ability of each of the activated mutant toxins to permeabilize M. sexta midgut brush border membrane vesicles was examined with an osmotic swelling assay. Following a 1-h preincubation, all mutants except the V150C mutant were able to form pores at pH 7.5, although the W182C mutant had a weaker activity than the other toxins. Increasing the pH to 10.5, a procedure which introduces a negative charge on the thiol group of the cysteine residues, caused a significant reduction in the pore-forming abilities of most mutants without affecting those of Cry1Aa or the I88C, T122C, Y153C, or S252C mutant. The rate of pore formation was significantly lower for the F50C, Q151C, Y153C, W182C, and S252C mutants than for Cry1Aa at pH 7.5. At the higher pH, all mutants formed pores significantly more slowly than Cry1Aa, except the I88C mutant, which formed pores significantly faster, and the T122C mutant. These results indicate that domain I interhelical loop residues play an important role in the conformational changes leading to toxin insertion and pore formation.Once ingested by susceptible insect larvae, the insecticidal crystal proteins of Bacillus thuringiensis are solubilized and converted to their toxic form by midgut proteases. The activated toxins bind to specific receptors on the surface of the luminal membrane of midgut columnar cells, insert into the membrane, and form pores that abolish transmembrane ionic gradients and osmotic balance, leading to the disruption of the epithelium and death of the insect (47, 51). Members of the B. thuringiensis Cry toxin family for which the atomic structure has been reported share a similar three-domain organization in which domain I is composed of a bundle of six amphipathic α-helices surrounding a hydrophobic helix (α5), and domains II and III are formed mostly of β-sheets (7, 8, 18, 26, 37, 38, 43). While domains II and III are thought to be involved in receptor binding and toxin specificity (47), domain I is believed to play a major role in membrane insertion and pore formation (51). Toxin fragments corresponding to domain I of Cry1Ac (62), Cry3Aa (53), and Cry3Ba (61) or to the first five α-helices of Cry4B (48) have been shown to form pores in model membranes. Pore formation in artificial membranes has also been demonstrated with synthetic peptides corresponding to α5 of Cry1Ac (13) and Cry3Aa (19, 21) and to the α4-loop-α5 segment of Cry3Aa (23). Spectroscopic studies have also revealed that while synthetic peptides corresponding to α4 and α5 can coassemble within a lipid bilayer, those corresponding to α2, α3, α6, and α7 adopt a membrane surface orientation (20, 22). In agreement with these findings, α4 was shown to line the lumen of the pores (42). On the other hand, convincing evidence supporting previous suggestions that most of the toxin molecule may become imbedded in the membrane (3, 39, 60) has recently been reported (44, 45).Thus, several models have been proposed for the mechanism of toxin insertion and pore formation (4, 9, 28, 32, 39, 44, 52, 56). Although these models differ in the identities of the toxin segments that are suggested to insert into the membrane, they all imply that the toxin undergoes conformational changes following binding to the membrane surface. Even though such changes imply rotations about the polypeptide backbone in domain I interhelical loops, little attention has been devoted so far to the role of domain I loop residues in pore formation.In the present study, amino acid residues strategically located within each of these loops in Cry1Aa were replaced by a cysteine using site-directed mutagenesis. The resulting mutant toxins were assayed with Manduca sexta midgut brush border membrane vesicles using a light-scattering technique. Mutations mapping within several of these loops altered the functional properties of Cry1Aa, suggesting the involvement of most domain I α-helices in the pore-forming process.