In the year 2014-2015, we continued to focus on three major research areas: 1) screening and characterizing drugs for combination therapy and transmission blocking; 2) studying the molecular mechanisms of malaria pathogenesis using Plasmodium yoelii/mouse model; 3) determining the molecular basis of an oocyst development defect. 1) In collaboration with scientists in NCATS, we synthesized and tested some derivatives of a promising compound that interacts with many current antimalarial drugs. Two of the derivatives showed higher potency (20 fold) in killing both sexual and asexual parasites. We are making and testing additional derivatives and are working towards bringing the compounds for animal and clinical trials. We have also been planning to test another compound (ketotifen) for transmission blocking in the field. Our manuscript from our combinational screening for antimalarial therapies has been submitted to Scientific Reports. 2) Using the rodent malaria parasite Plasmodium yoelii, we have made progresses in studying parasite-host interaction in several directions: I. Last year, we performed a genome-wide linkage analysis on host responses to infection of progeny from a P. yoelii genetic cross and identified hundreds of parasite genetic loci linked to responses of many host genes. We also clustered host genes based on their genome-wide patterns of LOD scores (GPLS) in response to parasite infections, which allowed accurate prediction of gene function. We then tested 15 genes (and verified 14) predicted to play a role in type I interferon response using various functional assays. This work developed a novel approach to predict host gene functions in response to parasite infection and a database with clusters of genes predicted to function in related pathways (Cell Rep 2015; 12: 661-672). II. We performed several additional crosses of P. y. negeriensis N67 and P. y. yoelii YM and have obtained 43 independent recombinant progeny. After characterizing the genotypes and phenotypes of the progeny, we identified some candidate genes linked to various phenotypes, including a gene encoding a putative E3 ubiquitin ligase. Although we have not been able to disrupt the gene in the parasite, we were able to insert a plasmid at 5 untranslated region (5UTR) and showed that the insertion changed the gene expression level and parasite growth pattern. We are performing additional experiments to modify the gene to better characterize the gene function. III. We also crossed P. berghei ANKA and P. berghei NK165 and obtained seven progeny to identify genes linked to cerebral malaria last year. We sequenced the genomes of the progeny and identified 20 polymorphisms. Additional progeny have been obtained and are being analyzed. IV. We are studying the molecular mechanism of apoptosis and necroptosis after P. yoelii infection. We are now focusing on pro-inflammatory responses mediated by IFN-gamma and are dissecting the molecular interactions and cell types contributing to inflammation after parasite infection. 3) We finished a project on mapping and functional characterization of a gene linked to an oocyst development defect. Through linkage mapping, gene knockout (KO) and gene complementation, we showed that the parasites sexual specific small subunit ribosomal RNA (D-ssu) plays an essential role in oocyst development. Additionally, we demonstrated that the P. yoelii D-ssu could regulate its oocyst development in a strain- and stage-specific manner, showing that ribosomal RNAs can regulate gene expression in addition to protein translation (mBio 2015, 6: e00117-15). Additionally, in collaboration with scientists and students at Xiamen University, China, we solved a century-old puzzle on a bird blood parasite Leucocytozoon sabrazesi. Because avian red blood cells have nuclei, and the parasite infection dramatically change the morphology of the host cells, it has been difficult to identify the infected cells. For a long time, the host cells invaded by Leucocytozoon gametocytes were believed to be red and/or white blood cells. Our recent study using cell type specific antibodies demonstrated that the Leucocytozoon gametocytes infect thrombocytes, a cell equivalent to human platelets, not other cell types (PLoS ONE 2015; 10: e0133478).
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