The transcriptome of Plasmodium vivax reveals divergence and diversity of transcriptional regulation in malaria parasites

Statistical estimation of cell-cycle progression and lineage commitment in Plasmodium falciparum reveals a homogeneous pattern of transcription in ex vivo culture

We have cultured Plasmodium falciparum directly from the blood of infected individuals to examine patterns of mature-stage gene expression in patient isolates. Analysis of the transcriptome of P. falciparum is complicated by the highly periodic nature of gene expression because small variations in the stage of parasite development between samples can lead to an apparent difference in gene expression values. To address this issue, we have developed statistical likelihood-based methods to estimate cell cycle progression and commitment to asexual or sexual development lineages in our samples based on microscopy and gene expression patterns. In cases subsequently matched for temporal development, we find that transcriptional patterns in ex vivo culture display little variation across patients with diverse clinical profiles and closely resemble transcriptional profiles that occur in vitro. These statistical methods, available to the research community, assist in the design and interpretation of P. falciparum expression profiling experiments where it is difficult to separate true differential expression from cell-cycle dependent expression. We reanalyze an existing dataset of in vivo patient expression profiles and conclude that previously observed discrete variation is consistent with the commitment of a varying proportion of the parasite population to the sexual development lineage.

The pathophysiology of vivax malaria

Long considered a benign infection, Plasmodium vivax is now recognized as a cause of severe and fatal malaria, despite its low parasite biomass, the increased deformability of vivax-infected red blood cells and an apparent paucity of parasite sequestration. Severe anemia is associated with recurrent bouts of hemolysis of predominantly uninfected erythrocytes with increased fragility, and lung injury is associated with inflammatory increases in alveolar-capillary membrane permeability. Although rare, vivax-associated coma challenges our understanding of pathobiology caused by Plasmodium spp. Host and parasite factors contribute to the risk of severe disease, and comorbidities might contribute to vivax mortality. In this review, we discuss potential mechanisms underlying the syndromes of uncomplicated and severe vivax malaria, identifying key areas for future research.

Reality check for malaria proteomics

Post-translationally modified protein isoforms are common in red blood cell stages of the malaria parasite.

New studies highlight the wide diversity of post-translational protein modifications in the intra-erythrocytic stages of the malaria parasite, raising new avenues for inquiry.

Rapid changes in transcription profiles of the Plasmodium yoelii yir multigene family in clonal populations: lack of epigenetic memory?

The pir multigene family, found in the genomes of Plasmodium vivax, P. knowlesi and the rodent malaria species, encode variant antigens that could be targets of the immune response. Individual parasites of the rodent malaria Plasmodium yoelii, selected by micromanipulation, transcribe only 1 to 3 different pir (yir) suggesting tight transcriptional control at the level of individual cells. Using microarray and quantitative RT-PCR, we show that despite this very restricted transcription in a single cell, many yir genes are transcribed throughout the intra-erythrocytic asexual cycle. The timing and level of transcription differs between genes, with some being more highly transcribed in ring and trophozoite stages, whereas others are more highly transcribed in schizonts. Infection of immunodeficient mice with single infected erythrocytes results in populations of parasites each with transcriptional profiles different from that of the parent parasite population and from each other. This drift away from the original 'set' of transcribed genes does not appear to follow a preset pattern and "epigenetic memory" of the yir transcribed in the parent parasite can be rapidly lost. Thus, regulation of pir gene transcription may be different from that of the well-characterised multigene family, var, of Plasmodium falciparum.

Plasmodium vivax: who cares?

More attention is being focused on malaria today than any time since the world's last efforts to achieve eradication over 40 years ago. The global community is now discussing strategies aimed at dramatically reducing malarial disease burden and the eventual eradication of all types of malaria, everywhere. As a consequence, Plasmodium vivax, which has long been neglected and mistakenly considered inconsequential, is now entering into the strategic debates taking place on malaria epidemiology and control, drug resistance, pathogenesis and vaccines. Thus, contrary to the past, the malaria research community is becoming more aware and concerned about the widespread spectrum of illness and death caused by up to a couple of hundred million cases of vivax malaria each year. This review brings these issues to light and provides an overview of P. vivax vaccine development, then and now. Progress had been slow, given inherent research challenges and minimal support in the past, but prospects are looking better for making headway in the next few years. P. vivax, known to invade the youngest red blood cells, the reticulocytes, presents a strong challenge towards developing a reliable long-term culture system to facilitate needed research. The P. vivax genome was published recently, and vivax researchers now need to coordinate efforts to discover new vaccine candidates, establish new vaccine approaches, capitalize on non-human primate models for testing, and investigate the unique biological features of P. vivax, including the elusive P. vivax hypnozoites. Comparative studies on both P. falciparum and P. vivax in many areas of research will be essential to eradicate malaria. And to this end, the education and training of future generations of dedicated "malariologists" to advance our knowledge, understanding and the development of new interventions against each of the malaria species infecting humans also will be essential.

Plasmodium vivax and the importance of the subtelomeric multigene vir superfamily

Plasmodium vivax is responsible for more than 100 million clinical cases yearly. Unlike P. falciparum, in which infected red blood cells cytoadhere via variant proteins, avoiding passage through the spleen, P.-vivax-infected reticulocytes seem not to cytoadhere. However, a variant subtelomeric multigene vir family has been identified in P. vivax. Thus, questions remain about how P. vivax circulates through the spleen and the role of Vir proteins. In this review, the importance of the vir multigene superfamily is reviewed in the light of the completion of the entire genome sequence of P. vivax and from data gathered from experimental infections in reticulocyte-prone non-lethal malaria parasites and natural P. vivax infections.

The Plasmodium vivax Pv41 surface protein: identification and characterization

Recently, Plasmodium vivax has been related to nearly 81% of malaria cases reported in Central America and the Mediterranean. Due to the difficulty of culturing this parasite species in vitro, most studies on P. vivax have focused on the identification of new antigens by homology comparison with P. falciparum vaccine candidate proteins. In this study, we have identified and characterized a Pf41 homologue in P. vivax, hence named Pv41, by following such approach and using web-available bioinformatics databases, molecular techniques and immunochemistry assays. Pv41 protein is a 384-amino-acid-long antigen encoded by a single exon that exhibits two s48/45 domains characteristic of gametocyte surface proteins. We have also demonstrated Pv41 transcription and expression during late intra-erythrocytic parasite stages and defined its subcellular localization on the parasite surface.