This year, the BioMalPar conference took place for the 17th time, but the second time virtually. Three poster presenters stunned their peers with their visually attractive digital posters, presentations and research insights. Out of 90 posters, they received the best poster award by popular vote. Meet the winners!
Sex-specific genetic screens identify hundreds of Plasmodium fertility genes essential for the transmission of malaria parasites
Sexual reproduction of malaria parasites is essential for their transmission by mosquitoes. Biological processes required for Plasmodium fertility include the formation of gametocytes, their transformation into gametes in response to signals from the mosquito, fertilisation in the bloodmeal, meiosis, and the formation of an invasive ookinete. Stage-specific gene expression data suggest that hundreds of parasite genes are uniquely required for sexual reproduction, but previous gene knockout studies have merely scratched the surface of this important aspect of parasite biology. We have mutagenised P. berghei lines that make only fertile male or only fertile female gametocytes, with barcoded PlasmoGEM vectors to screen >1200 targetable genes for sex-specific phenotypes. Our screens identify hundreds of genes with sex-specific roles. The data recapitulate existing knowledge of Plasmodium fertility and assign functions to previously unannotated genes. For the first time, we are gaining an unbiased picture of the molecular mechanisms of Plasmodium fertility at genome-scale, which will lead to a deeper understanding of this novel biology that could serve as targets for transmission blocking drugs or vaccines.
ABCI3 confers pleiotropic drug resistance to antimalarial compounds
Understanding the mechanisms available to the malaria parasite for acquiring multidrug resistance will be important for predicting which genes may become important for clinical resistance in the future.
ABC transporters are an important protein family with roles in drug resistance across a variety of organisms, and mutations in PfMDR1 modulate sensitivity to multiple antimalarials. Several other ABC transporters are encoded in the Plasmodium genome, and we have identified mutations in ABCI3 that confer resistance to several experimental antimalarial compounds.
Using in vitro drug selection regimes with a set of four chemically related compounds (SY4, 10, 11, 13), we isolated 12 drug resistant lines that were subjected to whole genome sequencing. All contained either single nucleotide variants (SNVs) or copy number amplifications of abci3. The point mutations were located in or near predicted transmembrane domains, consistent with a role in modifying the substrate specificity of the transporter, and testing of these lines against other compounds chemically-unrelated to the SY series identified a subset to which sensitivity is also affected.
In addition, natural variants of ABCI3 are observed at or near to these putative resistance SNVs, and preliminary evidence indicates differing sensitivities to the SY compounds among field isolates and common lab strains that may be driven by variation in ABCI3.
This work suggests abci3 should be among the genes monitored for changes in prevalence in longitudinal sampling of field isolates.
Characterization of a new malaria vaccine candidate against Plasmodium vivax using genetically modified rodent malaria parasites
Malaria, a mosquito-borne disease caused by Plasmodium parasites, is the most prevalent parasitic infection worldwide. Despite considerable efforts, there is still no effective vaccine against human-infective Plasmodium parasites, of which P. falciparum (Pf) and P. vivax (Pv) are the clinically most significant. Whole-sporozoite (Wsp) vaccines, which induce efficient immune responses against the pre-erythrocytic (PE) stages of Plasmodium parasites, are among the most promising immunization strategies so far. Although most malaria vaccine research has focused on Pf infection, Pv continues to be the most widespread of the human-infective Plasmodium species, imposing significant health and economic burdens on affected countries. Importantly, Pv can originate dormant parasitic liver forms – hypnozoites – which may cause malaria relapses long after mosquito transmission. Recently, our lab developed a new Wsp based on the use of transgenic rodent P. berghei (Pb) parasites as a platform to deliver immunogens of human-infective Plasmodium parasites. Since our in silico studies predict that >60% of CD8+ T cell epitopes encoded in both the Pv and Pb proteomes are shared between these two parasites, we generated a new genetically modified Pb expressing the highly immunogenic circumsporozoite (CS) protein from Pv (PvCS), in addition to its endogenous CS, Pb(PvCS@UIS4), to be used as a vaccine candidate against Pv malaria. Our immunofluorescence microscopy studies confirmed that both the endogenous PbCS and the inserted PvCS are expressed during the PE stages of this transgenic parasite, and that its infectivity is similar to that of its wild-type (WT) counterpart. Specifically, the ability of Pb(PvCS@UIS4) to infect Anopheles stephensi mosquitoes, as measured by the number of oocysts or sporozoites formed, as well as its ability to infect and develop normally in mouse hepatocytes and red blood cells showed no significant differences from those observed for WT parasites. Subsequent studies showed that mice immunization with Pb(PvCS@UIS4) elicits the production of anti-PvCS antibodies that efficiently recognize and bind to Pv sporozoites. Considering the lack of efficient strategies to tackle Pv, this study represents a crucial step on the development of a new Wsp vaccine candidate against this parasite.