415 research outputs found
Exploration and characterization of the conoid complex in <i>Plasmodium falciparum</i> merozoites
No full textPlasmodium falciparum, the deadliest malaria parasite, poses a significant global health threat. Belonging to the Apicomplexa phylum, Plasmodium parasites have an apical complex crucial for motility and host cell invasion. The conoid, a dynamic organelle of elusive function composed of spiraling tubulin fibers, was previously thought to be lost in Plasmodium. Recent evidence from the host laboratory challenges this belief, identifying conoid complex proteins and an apical tubulin ring (ATR) in the ookinete stage responsible for colonizing the mosquito midgut. Preliminary investigations suggest a further reduction of the conoid complex at the merozoite stage, responsible for invading human red blood cells. This master’s thesis explores the conoid complex in P. falciparum merozoites, examining the expression of key components shared with other apicomplexan parasites, such as Myosin B (MyoB), double-cortin domain (DCX), and apical annuli protein 4 (AAP4). Using expansion microscopy (U-ExM), we confirm the expression of a conoid complex by observing a MyoB-GFP ring. However, no tubulin ring is observed, suggesting a reductive evolution of the conoid complex at the merozoite stage. In addition, we provide evidence that DCX plays an unexpected role in a distinct noninvasive stage that does not express a conoid. Generating a mixed population of PfAAP4-DiCre-HA parasites marked a significant step in understanding AAP4's role in the conoid complex. Our findings reveal that the conoid complex in P. falciparum merozoites is minimally conserved and that conoid proteins might be repurposed in non-invasive stages.Plasmodium falciparum, le parasite responsable du paludisme le plus mortel, représente une menace majeure pour la santé mondiale. En tant que membre du phylum des apicomplexes, les parasites Plasmodium possèdent un complexe apical essentiel pour leur mobilité et leur capacité à envahir les cellules hôtes. Le conoïde, une structure dynamique composée de fibres de tubuline en spirale, a une fonction encore peu connue. Bien que traditionnellement considéré comme perdu chez Plasmodium, les recherches menées par le laboratoire de Mathieu Brochet remettent en question cette notion en identifiant des protéines du complexe conoïde et un anneau de tubuline apical (ATR) au stade ookinète, qui est responsable de la colonisation de l'intestin du moustique. Des investigations préliminaires suggèrent une réduction supplémentaire du complexe conoïde au stade mérozoïte, responsable de l'invasion des globules rouges humains. Cette thèse de master explore le complexe conoïde chez les mérozoïtes de P. falciparum en examinant l'expression de composants clés partagés avec d'autres parasites apicomplexes, tels que la Myosine B (MyoB), le domaine double-cortine (DCX) et la protéine annulaire apicale 4 (AAP4). Nos expériences de microscopie d'expansion (U-ExM) confirment l'expression d'un complexe conoïde par l'observation d'un anneau MyoB-GFP. Cependant, aucun anneau de tubuline n'est observé, suggérant une évolution réductive du complexe conoïde au stade mérozoïte. De plus, nous apportons des preuves que DCX joue un rôle inattendu dans un stade non invasif distinct qui n'exprime pas de conoïde. La génération d'une population mixte de parasites PfAAP4-DiCre-HA constitue une avancée significative dans la compréhension du rôle de AAP4 dans le complexe conoïde. Nos résultats indiquent que le complexe conoïde chez les mérozoïtes de P. falciparum est conservé de manière minimale et que certaines protéines associées au conoïde pourraient être réaffectées dans des stades non invasifs du parasite
Henri Brochet et le R.P. Émile Legault, c.s.c. : rencontre et correspondance
No full textCet article propose l’édition de 16 lettres qu’échangèrent le R.P. Émile Legault, c.s.c., et Henri Brochet, entre le 31 janvier 1938 et le 4 mai 1946. Ces lettres nous fournissent des renseignements intéressants sur le séjour d’Émile Legault en France, au lendemain de la visite de Henri Ghéon à Montréal, et sur les débuts des Compagnons de Saint-Laurent . Auteur prolifique de pièces de théâtre chrétien, acteur, metteur en scène, directeur des Compagnons de Jeux — dont s’inspirent les Compagnons de Saint-Laurent —, et ami de Henri Ghéon, Henri Brochet était aussi le fondateur de la revue Jeux, Tréteaux et Personnages, dont le premier numéro parut le 15 octobre 1930 et qu’il dirigea jusqu’à la fin.This article proposes the edition of 16 letters exchanged between Father Émile Legault, CSC, and Henri Brochet from January 31, 1938 to May 4, 1946. These letters offer interesting details on Émile Legault’s sojourn in France following the visit of Henri Ghéon to Montreal and on the beginnings of the Compagnons de Saint-Laurent. A prolific author of Christian plays, an actor, producer and director of the Compagnons de Jeux—which inspired the Compagnons de Saint-Laurent—and a friend of Henri Ghéon, Henri Brochet was also the founder of the journal Jeux, Tréteaux et Personnages, the first issue of which was published October 15, 1930 and which he edited until his death
Regulation of <i>Plasmodium</i> Gametogenesis
No full textMalaria is a major public health issue, responsible for 400 000 deaths every year. It is caused by Plasmodium parasites that circulate between vertebrate hosts and mosquito vectors. During this thesis, I focused on gametogenesis, a fascinating developmental stage to study Ca2+ signalling and regulation of the cell cycle in Plasmodium. Within seconds of activation, the cGMP- dependent protein kinase G (PKG) leads to mobilization of intracellular Ca2+. This is followed by a cascade of signalling events that in the male gametocyte regulates cell cycle progression to produce eight flagellated male gametes within ~10-12 minutes of the initial activation. I have identified a cGMP signalling platform involved in sensing extracellular cues activating gametogenesis and discovered a putative Ca2+ channel. Altogether my work sheds light into how Plasmodium transitions between host and vector and how it integrates and transduces cues from its environment to time its development.</p
Sensing extracellular cues via cGMP signaling in <i>Plasmodium</i> parasites
No full textMalaria remains a major public health problem despite significant eradication efforts, killing more than half a million people every year and putting nearly half the world’s population at risk. It is caused by unicellular eukaryotic Plasmodium parasites, which are transmitted via mosquito bites and replicate through a complex life cycle with several distinct stages involving both the vertebrate and the insect hosts.
During their life cycle, Plasmodium parasites must continually adapt to changing environments for successful proliferation and transmission. However, how they sense their surroundings to adapt their development remains a mystery, as they lack known receptors but can yet respond to extracellular signals.
In this thesis, I investigated how extracellular signals modulate cGMP homeostasis during transmission of Plasmodium gametocytes. Our findings show that a protein UGO (Unique GC Organizer) plays a crucial role in upregulating activity of the guanylyl cyclase GCα in response to extracellular cues. We also demonstrate that a signaling linking factor (SLF) is required for full basal GCα activity and optimal upregulation, and identified temperature-dependent epistatic interactions among two phosphodiesterases, PDEα and PDEδ.
Furthermore, we could show that premature activation of gametocytes at 37°C leads to abortive gametogenesis. A medium-throughput screening of approximately 4,000 compounds in P. berghei gametocytes identified several molecules capable of activating gametocytes by phenocopying XA mode of action, with the antidepressant sertraline showing particularly promising results. Interestingly, sertraline also shows a fast-killing activity against P. falciparum asexual blood stages in vitro. While the mode of action of sertraline in asexual blood stages remains to be identified, characterizing its target can pave the way for the development of novel multistage anti-Plasmodium molecules.</p
Cell cycle, motility and invasion: CDPK4 is a pleiotropic regulator across the lifecycle of parasites causing malaria
No full textIn Plasmodium, calcium-dependent protein kinase 4 (CDPK4) is essential for the process of male gametogenesis, where eight flagellated male gametes are produced from a single male gametocyte in ten minutes. This thesis characterised the molecular roles of CDPK4 during male gametogenesis and identified substrates of CDPK4 which mediate the respective molecular processes. CDPK4 mediates the initiation of DNA replication and promotes mitotic spindle formation through SOC1 and SOC2, and initiates axoneme motility through SOC3. A subsequent study uncovered a functional interaction network involving CDPK4, the cGMP-dependent protein kinase (PKG) and another CDPK of the same family, CDPK1, persevered in multiple life cycle stages. Upstream PKG mobilises intracellular calcium and subsequently activates CDPK4 and CDPK1, which mediate erythrocyte invasion and parasite motility in the mosquito gut. A substrate of CDPK4, SOC6 which mediates the aforementioned processes is equally involved in erythrocytic and mosquito stages
cGMP Signalling: Malarial Guanylyl Cyclase Leads the Way
No full textWhen ingested by a mosquito, the malaria parasite relies on an unusual form of gliding motility to escape from the rapidly deteriorating blood meal. A new study on an atypical malaria guanylyl cyclase reveals the importance of spatiotemporal regulation of cGMP production in this process
Végétation propice à la reproduction de la perchaude et du grand brochet et gestion des prairies dans la plaine inondable du lac Saint-Pierre
No full textLe lac Saint-Pierre, qui contient la plus vaste plaine d’inondation du fleuve Saint-Laurent, procure d’importants habitats pour la faune durant la crue printanière. Les terres agricoles cultivées dans sa plaine inondable sont dominées par des cultures de maïs et de soya, qui ont engendré des pertes d’habitat et contribué au déclin de la perchaude (Perca flavescens) et du grand brochet (Esox lucius). Afin d’améliorer les pratiques agricoles en bordure du lac Saint-Pierre, la présente étude visait à caractériser le couvert végétal utilisé par ces 2 espèces pour la fraie et à identifier la période de fauche des prairies cultivées permettant de recréer les caractéristiques propices à leur reproduction. Les sites de ponte étaient composés majoritairement d’alpiste roseau (Phalaris arundinacea) et d’autres plantes herbacées dressées au port rigide. Un modèle conçu pour estimer la probabilité de trouver des oeufs au printemps affichait des valeurs de 50 à 95 % lorsque la hauteur de la végétation se situait entre 50 et 90 cm l’automne précédent. L’aménagement de prairies naturelles ou cultivées de façon extensive, à raison d’une récolte réalisée entre la mi-juillet et la fin-juillet, produirait des habitats pour la perchaude et pour le grand brochet tout en protégeant la nidification des oiseaux champêtres. La présente étude suggère qu’avec des usages plus extensifs, une conciliation entre les besoins de la faune et une exploitation agricole de la plaine inondable du lac Saint-Pierre est possible.The Lac Saint-Pierre (Lake Saint-Pierre) (Québec, Canada) includes the largest floodplain of the St. Lawrence River and provides important wildlife habitat, particularly during spring flooding. Corn and soybean now dominate agricultural production throughout the floodplain, which has caused habitat loss for, and contributed to the decline of, yellow perch (Perca flavescens) and northern pike (Esox lucius). The present study aimed to provide scientific data to help improve agricultural practices in the floodplain to favour these 2 species by characterizing the plant cover used for spawning and identifying the mowing regime of cultivated grasslands that helped retain these characteristics. Spawning sites were composed mostly of reed canary grass (Phalaris arundinacea) and other rigid upright herbaceous plants. The probability of finding eggs during spring floods was 50% to 95% when the vegetation height the previous fall was between 50 cm and 90 cm. The restoration of natural meadows or extensively managed grasslands with a single hay harvest done in the second half of July, would provide spring spawning habitat for yellow perch and northern pike, and protect nesting grassland birds. This study suggests that with more extensive management, it should be possible to reconcile the needs of wildlife and agriculture in the Lac Saint-Pierre floodplain
Characterising two P. falciparum transporters essential for life cycle progression
No full textMalaria-Parasiten nutzen ein komplexes Repertoire aus Transportern, um sich durch ihren Lebenszyklus hindurch mit Nährstoffen aus Wirtszellen zu versorgen. Der Großteil der 144 Transporter von P. falciparum ist als essenziell für asexuelles Blutwachstum klassifiziert. Meine Hypothese war, dass ein Teil der bisher nicht untersuchten Transporter eine spezifische und essenzielle Rolle in den sexuellen Blutstadien von P. falciparum übernimmt und als Angriffspunkt dienen könnte, um die Transmission der Parasiten zu blockieren. Aus dem Transportom von P. falciparum wurden vielversprechende Gene identifiziert und durch experimentell-genetische Verfahren untersucht. Auf diesem Weg konnte ich einen Defekt bestätigen, der durch Fehlen von PfGEP1 hervorgerufen und bereits in der verwandten Spezies P. yoelii beschrieben wurde. Weder männliche noch weibliche Gametozyten konnten ohne GEP1 in der Lage Gameten bilden. Dies deutet auf eine zentrale Rolle für GEP1 in der Gametozyten-Aktivierung hin. Entsprechend groß ist das Potential, durch spezifische Inhibition von GEP1 die Übertragung von Malaria-Parasiten effizient zu unterbinden. Unterbrechung eines zweiten Gens namens MCP2 hatte keinen Effekt auf die Gametozyten von P. falciparum. Stattdessen wies P. berghei nach Fehlen von MCP2 einen Defekt bei der Sporozoitenbildung im Mitteldarm der Mücke auf. Nur in vereinzelten Oozysten konnten Sporozoiten gefunden werden und die Speicheldrüsen der infizierten Mücken enthielten kaum Sporozoiten. Somit hat die MCP2-Deletion keinen direkten Einfluss auf die Transmission vom Säugetierwirt auf die Mücke, jedoch erscheint MCP2 nötig für die Komplettierung des Lebenszyklus. Zusammenfassend bestätigen meine Daten die These, dass Transporterproteine in mindestens einem Stadium des Lebenszyklus von Plasmodium eine essenzielle Rolle spielen und liefern weitere Einblicke in die Funktion dieser Proteine.During life cycle progression, Plasmodium parasites rely on a complex repertoire of transporter proteins to supply them with nutrients obtained from their host. Of the 144 transporter proteins annotated in Plasmodium falciparum, the majority has already been deemed likely essential for asexual blood growth. In this thesis, I hypothesized that a part of the unassigned parasitic transportome will be specifically essential to the sexual gametocyte stages and thus could contain transmission blocking targets for future application. The transportome of P. falciparum was screened in silico for potential candidates and the most promising genes were then targeted via a Crispr-Cas9-based disruption approach. Through this, I was able to confirm a defect in gametogenesis caused by disruption of PfGEP1 previously observed in P. yoelii. Both male and female gametocytes lacking GEP1 were unable to produce gametes. Overall, my data indicates that GEP1 plays a central role in the activation process, making it a promising transmission blocking target. Disruption of a second candidate gene called MCP2 did not affect P. falciparum asexual and sexual blood stages. Deletion of its P. berghei ortholog instead resulted in impaired sporozoite formation in the mosquito vector. While parasites lacking PbMCP2 were able to infect mosquito midguts and form oocysts, only few of them appeared to produce midgut sporozoites. Consequently, very few sporozoites colonized mosquito salivary glands. While lack of MCP2 does not seem to affect vertebrate-to-mosquito transmission as anticipated, it appears necessary for life cycle progression. Together, the findings presented here underline the importance of transporter proteins for Plasmodium parasites throughout their life cycle and contribute to our understanding of their roles in the different life cycle stages of malarial parasites
Expansion microscopy of Plasmodium gametocytes reveals the molecular architecture of a bipartite microtubule organisation centre coordinating mitosis with axoneme assembly
No full textTransmission of malaria-causing parasites to mosquitoes relies on the production of gametocyte stages and their development into gametes. These stages display various microtubule cytoskeletons and the architecture of the corresponding microtubule organisation centres (MTOC) remains elusive. Combining ultrastructure expansion microscopy (U-ExM) with bulk proteome labelling, we first reconstructed in 3D the subpellicular microtubule network which confers cell rigidity to Plasmodium falciparum gametocytes. Upon activation, as the microgametocyte undergoes three rounds of endomitosis, it also assembles axonemes to form eight flagellated microgametes. U-ExM combined with Pan-ExM further revealed the molecular architecture of the bipartite MTOC coordinating mitosis with axoneme formation. This MTOC spans the nuclear membrane linking cytoplasmic basal bodies to intranuclear bodies by proteinaceous filaments. In P. berghei, the eight basal bodies are concomitantly de novo assembled in a SAS6- and SAS4-dependent manner from a deuterosome-like structure, where centrin, γ-tubulin, SAS4 and SAS6 form distinct subdomains. Basal bodies display a fusion of the proximal and central cores where centrin and SAS6 are surrounded by a SAS4-toroid in the lumen of the microtubule wall. Sequential nucleation of axonemes and mitotic spindles is associated with a dynamic movement of γ-tubulin from the basal bodies to the intranuclear bodies. This dynamic architecture relies on two non-canonical regulators, the calcium-dependent protein kinase 4 and the serine/arginine-protein kinase 1. Altogether, these results provide insights into the molecular organisation of a bipartite MTOC that may reflect a functional transition of a basal body to coordinate axoneme assembly with mitosis
Génomique des populations et flux géniques au sein de l espèce streptococcus agalactiae
No full textPARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
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