The Origin of Intraspecific Variation of Virulence in an Eukaryotic Immune Suppressive Parasite

Occurrence of intraspecific variation in parasite virulence, a prerequisite for coevolution of hosts and parasites, has largely been reported. However, surprisingly little is known of the molecular bases of this variation in eukaryotic parasites, with the exception of the antigenic variation used by immune-evading parasites of mammals. The present work aims to address this question in immune suppressive eukaryotic parasites. In Leptopilina boulardi, a parasitic wasp of Drosophila melanogaster, well-defined virulent and avirulent strains have been characterized. The success of virulent females is due to a major immune suppressive factor, LbGAP, a RacGAP protein present in the venom and injected into the host at oviposition. Here, we show that an homologous protein, named LbGAPy, is present in the venom of the avirulent strain. We then question whether the difference in virulence between strains originates from qualitative or quantitative differences in LbGAP and LbGAPy proteins. Results show that the recombinant LbGAPy protein has an in vitro GAP activity equivalent to that of recombinant LbGAP and similarly targets Drosophila Rac1 and Rac2 GTPases. In contrast, a much higher level of both mRNA and protein is found in venom-producing tissues of virulent parasitoids. The F1 offspring between virulent and avirulent strains show an intermediate level of LbGAP in their venom but a full success of parasitism. Interestingly, they express almost exclusively the virulent LbGAP allele in venom-producing tissues. Altogether, our results demonstrate that the major virulence factor in the wasp L. boulardi differs only quantitatively between virulent and avirulent strains, and suggest the existence of a threshold effect of this molecule on parasitoid virulence. We propose that regulation of gene expression might be a major mechanism at the origin of intraspecific variation of virulence in immune suppressive eukaryotic parasites. Understanding this variation would improve our knowledge of the mechanisms of transcriptional evolution currently under active investigation

2.4 Les villages ecclésiaux dans le bassin de l'Aude

2.3 Ecclesiastical villages in the Aude basin D. BAUDREU, J.-P. CAZES A series of case studies illustrates the immediate surroundings of churches in the Aude basin located in western Languedoc. They show the relationship between settlements and places of worship during the Romanesque period. The generic term ecclesiastic village is used to define these sites which have various forms due to building materials, evolution over time, or to spatial organisation (open or circularly-enclosed settlement cores). The circular structures correspond to sacred perimeters, with a radius of thirty paces, which were given ecclesiastic immunity by the eleventh- century Peace of God councils. In the context of medieval village development, this first settlement concentration process preceded the castrai agglomerations which multiply during the XVIIth century at the expense of existing groups.2.4 Les villages ecclésiaux dans le bassin de l'Aude D. BAUDREU, J.-P. CAZES Une série de cas illustre l'environnement immédiat d'églises du bassin de l'Aude, en Languedoc occidental, et souligne l'articulation entre habitats et lieux de culte d'époque romane. Sous la diversité des formes due aux matériaux de construction, à l'évolution dans le temps ou à l'organisation spatiale (groupements ouverts, noyaux circulaires enclos), les sites sont définis par le terme générique de villages ecclésiaux. Les structures circulaires correspondent aux périmètres sacrés de trente pas de rayon dotés de l'immunité ecclésiastique par les conciles de la Paix de Dieu au XIe s. Replacé dans le contexte de la naissance du village médiéval, ce premier processus de concentration précède les agglomérations castrales qui se multiplient au XIIe s. au détriment des groupements existants.Baudreu Dominique, Cazes Jean-Paul. 2.4 Les villages ecclésiaux dans le bassin de l'Aude. In: L'environnement des églises et la topographie religieuse des campagnes médiévales. Actes du IIIe congrès international d'archéologie médiévale (Aix-en-Provence, 28-30 septembre 1989) Caen : Société d'Archéologie Médiévale, 1994. pp. 80-97. (Actes des congrès de la Société d'archéologie médiévale, 3

2.4 Les villages ecclésiaux dans le bassin de l'Aude

2.3 Ecclesiastical villages in the Aude basin D. BAUDREU, J.-P. CAZES A series of case studies illustrates the immediate surroundings of churches in the Aude basin located in western Languedoc. They show the relationship between settlements and places of worship during the Romanesque period. The generic term ecclesiastic village is used to define these sites which have various forms due to building materials, evolution over time, or to spatial organisation (open or circularly-enclosed settlement cores). The circular structures correspond to sacred perimeters, with a radius of thirty paces, which were given ecclesiastic immunity by the eleventh- century Peace of God councils. In the context of medieval village development, this first settlement concentration process preceded the castrai agglomerations which multiply during the XVIIth century at the expense of existing groups.2.4 Les villages ecclésiaux dans le bassin de l'Aude D. BAUDREU, J.-P. CAZES Une série de cas illustre l'environnement immédiat d'églises du bassin de l'Aude, en Languedoc occidental, et souligne l'articulation entre habitats et lieux de culte d'époque romane. Sous la diversité des formes due aux matériaux de construction, à l'évolution dans le temps ou à l'organisation spatiale (groupements ouverts, noyaux circulaires enclos), les sites sont définis par le terme générique de villages ecclésiaux. Les structures circulaires correspondent aux périmètres sacrés de trente pas de rayon dotés de l'immunité ecclésiastique par les conciles de la Paix de Dieu au XIe s. Replacé dans le contexte de la naissance du village médiéval, ce premier processus de concentration précède les agglomérations castrales qui se multiplient au XIIe s. au détriment des groupements existants.Baudreu Dominique, Cazes Jean-Paul. 2.4 Les villages ecclésiaux dans le bassin de l'Aude. In: L'environnement des églises et la topographie religieuse des campagnes médiévales. Actes du IIIe congrès international d'archéologie médiévale (Aix-en-Provence, 28-30 septembre 1989) Caen : Société d'Archéologie Médiévale, 1994. pp. 80-97. (Actes des congrès de la Société d'archéologie médiévale, 3

Extracellular superoxide dismutase in insects: characterization, function and interspecific variation in parasitoid wasps' venom

International audienceEndoparasitoid wasps inject venom proteins with their eggs to protect them from the host immune response and ensure successful parasitism. Here, we report identification of intracellular (SOD1) and extracellular (SOD3) Cu,Zn superoxide dismutase transcripts in the venom apparatus of two Leptopilina species, parasitoids of Drosophila. Leptopilina SODs show sequence and structure similarity to human SODs, but phylogenetic analyses indicate that the extracellular SODs are more related to cytoplasmic vertebrate SODs than to extracellular ones, a feature shared by predicted insect extracellular SODs. We demonstrate that L. boulardi SOD3 (LbSOD3) is indeed secreted and active as monomeric glycosylated forms in venom. Our results also evidence quantitative variation in SOD3 venom contents between closely related parasitoid species since sod3 is 100-fold less expressed in L. heterotoma venom apparatus and no protein and SOD activity are detected in its venom. Leptopilina recombinant SOD3s as well as a mammalian SOD in vitro inhibit the Drosophila phenoloxidase activity in a dose-dependent manner, demonstrating that SODs may interfere with the Drosophila melanization process and therefore with production of cytotoxic compounds. Although the recombinant LbSOD3 quantity needed to observe this effect precludes a systemic effect of the wasp venom SOD3, it is still consistent with a local action at oviposition. This work provides the first demonstration that insect extracellular SODs are indeed secreted and active in an insect fluid and can be used as virulence factors to counteract the host immune response, a strategy largely used by bacterial and fungal pathogens but also protozoan parasites during infectio

A serpin from the parasitoid wasp Leptopilina boulardi targets the Drosophila phenoloxidase cascade

International audienceThe insect phenoloxidase (PO) cascade is known to be tightly regulated by serine proteases and serine protease inhibitors of the serpin family. As a key component of the insect immune system, it is also suspected to be inhibited by several endoparasitoid wasps, insects that develop inside other arthropods as hosts. However, the underlying mechanisms of this inhibition are largely undescribed. Here, we report the characterization of a gene encoding a serpin, LbSPNy, highly expressed in the venom of the wasp Leptopilina boulardi (ISy type), and we show that either the venom or the recombinant LbSPNy inhibit the PO cascade in the hemolymph of Drosophila yakuba host larva. Altogether, our results identify the first serpin used as a virulence factor by a parasitoid wasp and show that it disrupts the activation pathway of the PO in the Drosophila host

Closely related parasites targeting the same host can show extensive venom variation: the case of Leptopilina parasitoids of Drosophila

National audienc

Closely related parasites targeting the same host can show extensive venom variation: the case of Leptopilina parasitoids of Drosophila

National audienc