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Clinical malaria is associated with the proliferation of Plasmodium parasites in human erythrocytes. The coordinated processes of parasite egress from and invasion into erythrocytes are rapid and tightly regulated. We have found that the plant-like calcium-dependent protein kinase PfCDPK5, which is expressed in invasive merozoite forms of Plasmodium falciparum, was critical for egress. Parasites deficient in PfCDPK5 arrested as mature schizonts with intact membranes, despite normal maturation of egress proteases and invasion ligands. Merozoites physically released from stalled schizonts were capable of invading new erythrocytes, separating the pathways of egress and invasion. The arrest was downstream of cyclic guanosine monophosphate-dependent protein kinase (PfPKG) function and independent of protease processing. Thus, PfCDPK5 plays an essential role during the blood stage of malaria replication.

A fundamental problem in systems biology and whole genome sequence analysis is how to infer functions for the many uncharacterized proteins that are identified, whether they are conserved across organisms of different phyla or are phylum-specific. This problem is especially acute in pathogens, such as malaria parasites, where genetic and biochemical investigations are likely to be more difficult. Here we perform comparative expression analysis on Plasmodium parasite life cycle data derived from P. falciparum blood, sporozoite, zygote and ookinete stages, and P. yoelii mosquito oocyst and salivary gland sporozoites, blood and liver stages and show that type II fatty acid biosynthesis genes are upregulated in liver and insect stages relative to asexual blood stages. We also show that some universally uncharacterized genes with orthologs in Plasmodium species, Saccharomyces cerevisiae and humans show coordinated transcription patterns in large collections of human and yeast expression data and that the function of the uncharacterized genes can sometimes be predicted based on the expression patterns across these diverse organisms. We also use a comprehensive and unbiased literature mining method to predict which uncharacterized parasite-specific genes are likely to have roles in processes such as gliding motility, host-cell interactions, sporozoite stage, or rhoptry function. These analyses, together with protein-protein interaction data, provide probabilistic models that predict the function of 926 uncharacterized malaria genes and also suggest that malaria parasites may provide a simple model system for the study of some human processes. These data also provide a foundation for further studies of transcriptional regulation in malaria parasites.

A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont.

The biodiversity of insect trypanosomes is largely unknown, resulting in significant gaps in the understanding of pathogen evolution. A culture-independent preliminary survey of trypanosomatid fauna was conducted for the parasites of Heteroptera (Hemiptera) from several localities in Costa Rica. Trypanosomatid infections were detected by light microscopy of smeared gut contents. Out of 257 insects representing 6 families, infections were found in 62 cases; cultures were obtained for 29 new isolates. Gut material from infected hosts was preserved in the field using an SDS-EDTA buffer solution for subsequent DNA extraction in the laboratory. PCR amplification of the trypanosomatid-specific spliced leader (SL) RNA gene repeats was successful for 60 field samples. Eighteen distinct SL RNA typing units were identified in a set of 28 samples analysed in detail. Cluster analysis indicated that these typing units were unique and thus could represent new species and, in some cases, new genera. This study reveals only a minor fraction of the trypanosomatid biodiversity, which is anticipated to be high.