Role of egg-laying behavior, virulence and local adaptation in a parasitoid's chances of reproducing in a new host.

Understanding the ability of parasitoid insects to succeed in new host populations is a relevant question for biological control and adaptive mechanisms. Cotesia typhae is an African parasitoid specialized on the moth Sesamiae nonagrioides, also called the Mediterranean corn borer. Two Kenyan strains of C. typhae differ in their virulence against a new host population from France. We explored behavioral and physiological hypotheses about this differentiation. Cotesia genus belongs to a group of Hymenoptera in which females inject a domesticated virus in their host to overcome its resistance. Since viral particles are injected along with eggs and since the strain with the higher virulence injects more eggs, we hypothesized that virulence could be explained by the quantity of virus injected. To test this assumption, we measured the injected quantities of eggs and viral particles (estimated by viral DNA segments) of each parasitoid strain along several ovipositions, to vary these quantities. Unexpectedly, results showed that virulence against the French host was not correlated to the injected quantities of eggs or viral segments, indicating that virulence differentiation is explained by other causes. The virulence against the respective natural hosts of the two C. typhae strains was also measured, and results suggest that local adaptation to a more resistant natural host may explain the pre-adaptation of one strain to the new host population. We also identified a differentiation of oviposition strategy and subsequent offspring number between the parasitoid strains, which is important in a biocontrol perspective.

Relationship between oviposition, virulence gene expression and parasitism success in Cotesia typhae nov. sp. parasitoid strains.

Studying mechanisms that drive host adaptation in parasitoids is crucial for the efficient use of parasitoids in biocontrol programs. Cotesia typhae nov. sp. (Fernández-Triana) (Hymenoptera: Braconidae) is a newly described parasitoid of the Mediterranean corn borer Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae). Braconidae are known for their domesticated bracovirus, which is injected with eggs in the host larva to overcome its resistance. In this context, we compared reproductive success traits of four Kenyan strains of C. typhae on a French and a Kenyan populations of its host. Differences were found between the four strains and the two most contrasted ones were studied more thoroughly on the French host population. Parasitoid offspring size was correlated with parasitism success and the expression of bracovirus virulence genes (CrV1 and Cystatin) in the host larva after parasitism. Hybrids between these two parasitoid strains showed phenotype and gene expression profiles similar to the most successful parental strain, suggesting the involvement of dominant alleles in the reproductive traits. Ovary dissections revealed that the most successful strain injected more eggs in a single host larva than the less successful one, despite an equal initial ovocyte number in ovaries. It can be expected that the amount of viral particles increase with the number of eggs injected. The ability to bypass the resistance of the allopatric host may in consequence be related to the oviposition behaviour (eggs allocation). The influence of the number of injected eggs on parasitism success and on virulence gene expression was evaluated by oviposition interruption experiments.

Comparing de novo and reference-based transcriptome assembly strategies by applying them to the blood-sucking bug Rhodnius prolixus.

High Throughput Sequencing capabilities have made the process of assembling a transcriptome easier, whether or not there is a reference genome. But the quality of a transcriptome assembly must be good enough to capture the most comprehensive catalog of transcripts and their variations, and to carry out further experiments on transcriptomics. There is currently no consensus on which of the many sequencing technologies and assembly tools are the most effective. Many non-model organisms lack a reference genome to guide the transcriptome assembly. One question, therefore, is whether or not a reference-based genome assembly gives better results than de novo assembly. The blood-sucking insect Rhodnius prolixus-a vector for Chagas disease-has a reference genome. It is therefore a good model on which to compare reference-based and de novo transcriptome assemblies. In this study, we compared de novo and reference-based genome assembly strategies using three datasets (454, Illumina, 454 combined with Illumina) and various assembly software. We developed criteria to compare the resulting assemblies: the size distribution and number of transcripts, the proportion of potentially chimeric transcripts, how complete the assembly was (completeness evaluated both through CEGMA software and R. prolixus proteome fraction retrieved). Moreover, we looked for the presence of two chemosensory gene families (Odorant-Binding Proteins and Chemosensory Proteins) to validate the assembly quality. The reference-based assemblies after genome annotation were clearly better than those generated using de novo strategies alone. Reference-based strategies revealed new transcripts, including new isoforms unpredicted by automatic genome annotation. However, a combination of both de novo and reference-based strategies gave the best result, and allowed us to assemble fragmented transcripts.

De novo transcriptome assembly for a non-model species, the blood-sucking bug Triatoma brasiliensis, a vector of Chagas disease.

High throughput sequencing (HTS) provides new research opportunities for work on non-model organisms, such as differential expression studies between populations exposed to different environmental conditions. However, such transcriptomic studies first require the production of a reference assembly. The choice of sampling procedure, sequencing strategy and assembly workflow is crucial. To develop a reliable reference transcriptome for Triatoma brasiliensis, the major Chagas disease vector in Northeastern Brazil, different de novo assembly protocols were generated using various datasets and software. Both 454 and Illumina sequencing technologies were applied on RNA extracted from antennae and mouthparts from single or pooled individuals. The 454 library yielded 278 Mb. Fifteen Illumina libraries were constructed and yielded nearly 360 million RNA-seq single reads and 46 million RNA-seq paired-end reads for nearly 45 Gb. For the 454 reads, we used three assemblers, Newbler, CAP3 and/or MIRA and for the Illumina reads, the Trinity assembler. Ten assembly workflows were compared using these programs separately or in combination. To compare the assemblies obtained, quantitative and qualitative criteria were used, including contig length, N50, contig number and the percentage of chimeric contigs. Completeness of the assemblies was estimated using the CEGMA pipeline. The best assembly (57,657 contigs, completeness of 80 %, <1 % chimeric contigs) was a hybrid assembly leading to recommend the use of (1) a single individual with large representation of biological tissues, (2) merging both long reads and short paired-end Illumina reads, (3) several assemblers in order to combine the specific advantages of each.

Intravenous infusion of donor apoptotic leukocytes before transplantation delays allogeneic islet graft rejection through regulatory T cells.

AIM: This study describes the ability of intravenous donor apoptotic leukocyte infusion before islet transplantation to delay allogeneic graft rejection and implicates regulatory T cells (T(reg)) in the effect. METHODS: Allogeneic FVB (Friend virus B-type) islet transplants were placed under the kidney capsule of BALB/c recipient mice rendered diabetic by streptozotocin. Apoptotic donor leukocytes were infused intravenously 7 days before transplantation. Foxp3/DTR/GFP transgenic C57BL/6 mice were used as recipients to show depletion of T(reg) after apoptotic cell infusion. Control mice received islet transplants without apoptotic cells. RESULTS: The graft median survival time (MST) in recipient mice was 15±1.5 days when apoptotic cells were infused 7 days prior to transplantation of a 1000-islet-containing allograft and 6±0.5 days in the control mice (P<0.01). The same effect was observed using a 500-islet allograft, with an MST of 9±1.1 days vs. 3±0.8 days with and without (controls) apoptotic cells, respectively (P<0.01). This immunomodulatory effect was not observed when apoptotic cell administration was performed on the day of transplantation. Specific T(reg) depletion in Foxp3/DTR/GFP recipient mice inhibited the beneficial effect of apoptotic cell infusion with an MST of 8±1.5 days after apoptotic cell infusion vs. 2±0.2 days when T(reg) were depleted (P<0.01). Furthermore, T(reg) were specifically detected in the islet grafts of mice infused with apoptotic cells prior to islet transplantation. CONCLUSION: Infusion of donor apoptotic cells 7 days before allogeneic transplantation delays islet allograft rejection through a process involving T(reg).

The potential role of glucagon-like peptide-1 or its analogues in enhancing glycaemic control in critically ill adult patients.

Intravenous insulin therapy is the gold standard therapy for glycaemic control in hyperglycaemic critically ill adult patients. However, hypoglycaemia remains a major concern in critically ill patients, even in some populations who are not receiving infused insulin. Furthermore, the influence of factors such as glycaemic variability and nutritional support may conceal any benefit of strict glycaemic control on morbidity and mortality in these patients. The recently revised guidelines of the American Diabetic Association/American College of Clinical Endocrinologists no longer advocate very tight glycaemic control or normalization of glucose levels in all critically ill patients. In the light of various concerns over the optimal glucose level and means to achieve such control, the use of glucagon-like peptide-1 or its analogues administered intravenously may represent an interesting therapeutic option.

Methylaminolaevulinate photodynamic therapy in patients with multiple basal cell carcinomas in the setting of Gorlin-Goltz syndrome or after radiotherapy.

BACKGROUND: The naevoid basal cell carcinoma syndrome (NBCCS) is a therapeutic challenge due to the multiplicity of cutaneous tumours. Photodynamic therapy (PDT) is increasingly used as an alternative treatment for superficial and in some countries nodular basal cell carcinomas (BCC). OBJECTIVE: To study the safety and efficiency of PDT in NBCCS. METHODS: We reviewed retrospectively the evolution of 62 lesions from patients with multiple BCC treated with PDT. RESULTS: The initial response rate (85.4%, 53/62) and recurrence rate (7.5%) appeared comparable to literature values in NBCCS and to those reported in the treatment of sporadic BCC. The clearance rate without recurrence was 79% (49/62), during a mean follow-up period of 13 months. The cosmetic outcome was excellent. Recurrences were found almost 2 years after treatment. CONCLUSION: PDT is a suitable therapeutic option in the management of NBCCS patients but requires a strict and long follow-up.

Genomic choice of codons in 16 microbial species.

We study the codon usage over whole set of ORFs of 16 unicellular microbial species: eight archaebacteria, seven eubacteria, and one eukarya. We first try to define, for each species, the neutral expected codon usage to better approach subsequently the influence of selection. Overlapping triplets counted from the complete DNA genomic sequence and mean amino acid composition of ORFs allow us to build satisfying expected codon usage for each species. Within species deviation from this neutral model is then studied through Correspondence Analysis and characterization with bias index, N(C)' (effective number of codons reported to neutral model). Our results are compared to previously published ones for three species and let appear good agreement in spite of very different methods. We thus propose set of codons probably preferred by selection for nine other species. In the four last species, no clear preference can be evidenced. Finally, we characterize variation of codon usage over functional categories. We propose that the high degree of bias of proteins involved in translation, ribosomal structure and biogenesis has a positive influence on overexpression of the corresponding genes under optimum growth conditions and is a negative regulator of the same genes when amino acids become limited resources.

Stationary distributions of microsatellite loci between divergent population groups of the European rabbit (Oryctolagus cuniculus).

Previous analysis of mitochondrial DNA polymorphism in the native range of the European rabbit (Oryctolagus cuniculus) demonstrated the occurrence of two highly divergent (2 Myr) maternal lineages with a well-defined geographical distribution. Analysis of both protein and immunoglobulin polymorphisms are highly concordant with this pattern of differentiation. However, the present analysis of nine polymorphic microsatellite loci (with a total of 169 alleles) in 24 wild populations reveals severe allele-size homoplasy which vastly underestimates divergence between the main groups of populations in Iberia. Nonetheless, when applied to more recent historical phenomena, this same data set not only confirms the occurrence of a strong bottleneck associated with the colonization of Mediterranean France but also suggests a two-step dispersal scenario that began with gene flow from northern Spain through the Pyrenean barrier and subsequent range expansion into northern France. The strength and appropriateness of applying microsatellites to more recent evolutionary questions is highlighted by the fact that both mtDNA and protein markers lacked the allelic diversity necessary to properly evaluate the colonization of France. The well-documented natural history of European rabbit populations provides an unusually comprehensive framework within which one can appraise the advantages and limitations of microsatellite markers in revealing patterns of genetic differentiation that have occurred across varying degrees of evolutionary time. The degree of size homoplasy presented in our data should serve as a warning to those drawing conclusions from microsatellite data sets which lack a set of complementary comparative markers, or involve long periods of evolutionary history, even within a single species.

Absence of a genetic bottleneck in a wild rabbit (Oryctolagus cuniculus) population exposed to a severe viral epizootic.

Infectious diseases and their demographic consequences are thought to influence the genetic diversity of populations. In Europe, during the last 50 years, the European rabbit (Oryctolagus cuniculus) has suffered two important viral epizootics: myxomatosis and rabbit viral haemorraghic disease (RVHD). Although mortality rates were very high, the impact of these diseases on genetic diversity has never been assessed directly. The subject of this paper is a wild rabbit population in France, which has been studied since the beginning of the 1980s. The first outbreak of RVHD occurred in 1995 and provoked a demographic crash. The population, sampled for the first time in 1982 and 1994, was sampled again at the end of 1996 to examine the impact of the epizootic on genetic diversity. In spite of the observed high mortality rate ( approximately 90%), analysis of 14 polymorphic loci (allozymes and microsatellites) showed no loss in genetic diversity after the epizootic. Determination of temporal changes in allele frequencies indicated that the population evolved under genetic drift. The temporal method of Waples demonstrated a significant decrease in the effective population size (Ne) correlated with the demographic crash due to the epizootic. However, the population had only been studied for two generations after the epizootic and the remnant population size probably stayed high enough ( approximately 50 individuals) to keep its genetic diversity at the precrash level. These results suggest that, contrary to what is usually thought and in spite of the subsequent high mortality rates, past epizootics (especially myxomatosis) may have had little effect on the genetic diversity of wild rabbit populations in Europe.