Dual fluorescent labelling of the human malaria parasite Plasmodium falciparum for the analysis of the ABC type transporter pfmdr2

Trio fluorophore-based phenotypic assay for the detection of artemisinin-induced growth-arrested Plasmodium falciparum in human erythrocytes

Artemisinin combination therapy remains effective for the treatment of falciparum malaria. However, Plasmodium falciparum can escape the effects of artemisinin by arresting their growth. The growth-arrested parasites cannot be distinguished from nonviable parasites with standard microscopy techniques due to their morphological similarities. Here, we demonstrated the efficacy of a new laboratory assay that is compatible with the artemisinin susceptibility test. As a result of the differential cell permeabilities of two DNA-binding fluorophores, growth-arrested P. falciparum can be distinguished from parasites killed by artemisinin, since the latter lose cell membrane permeability. This fluorescence-based assay increased the sensitivity and specificity of the ring survival assay in the assessment of artemisinin susceptibility. When combined with a third fluorophore-conjugated anti-human leukocyte antibody, this trio fluorophore assay became more useful in identifying growth-arrested parasites in mock human blood samples. This novel assay is a simple and rapid technique for monitoring artemisinin resistance with greater sensitivity and accuracy compared with morphology-based observations under a light microscope.

The transportome of the malaria parasite

Membrane transport proteins, also known as transporters, control the movement of ions, nutrients, metabolites, and waste products across the membranes of a cell and are central to its biology. Proteins of this type also serve as drug targets and are key players in the phenomenon of drug resistance. The malaria parasite has a relatively reduced transportome, with only approximately 2.5% of its genes encoding transporters. Even so, assigning functions and physiological roles to these proteins, and ascertaining their contributions to drug action and drug resistance, has been very challenging. This review presents a detailed critique and synthesis of the disruption phenotypes, protein subcellular localisations, protein functions (observed or predicted), and links to antimalarial drug resistance for each of the parasite's transporter genes. The breadth and depth of the gene disruption data are particularly impressive, with at least one phenotype determined in the parasite's asexual blood stage for each transporter gene, and multiple phenotypes available for 76% of the genes. Analysis of the curated data set revealed there to be relatively little redundancy in the Plasmodium transportome; almost two-thirds of the parasite's transporter genes are essential or required for normal growth in the asexual blood stage of the parasite, and this proportion increased to 78% when the disruption phenotypes available for the other parasite life stages were included in the analysis. These observations, together with the finding that 22% of the transportome is implicated in the parasite's resistance to existing antimalarials and/or drugs within the development pipeline, indicate that transporters are likely to serve, or are already serving, as drug targets. Integration of the different biological and bioinformatic data sets also enabled the selection of candidates for transport processes known to be essential for parasite survival, but for which the underlying proteins have thus far remained undiscovered. These include potential transporters of pantothenate, isoleucine, or isopentenyl diphosphate, as well as putative anion-selective channels that may serve as the pore component of the parasite's 'new permeation pathways'. Other novel insights into the parasite's biology included the identification of transporters for the potential development of antimalarial treatments, transmission-blocking drugs, prophylactics, and genetically attenuated vaccines. The syntheses presented herein set a foundation for elucidating the functions and physiological roles of key members of the Plasmodium transportome and, ultimately, to explore and realise their potential as therapeutic targets.

Coral cell separation and isolation by fluorescence-activated cell sorting (FACS)

BACKGROUND

Generalized methods for understanding the cell biology of non-model species are quite rare, yet very much needed. In order to address this issue, we have modified a technique traditionally used in the biomedical field for ecological and evolutionary research. Fluorescent activated cell sorting (FACS) is often used for sorting and identifying cell populations. In this study, we developed a method to identify and isolate different cell populations in corals and other cnidarians.

METHODS

Using fluorescence-activated cell sorting (FACS), coral cell suspension were sorted into different cellular populations using fluorescent cell markers that are non-species specific. Over 30 different cell markers were tested. Additionally, cell suspension from Aiptasia pallida was also tested, and a phagocytosis test was done as a downstream functional assay.

RESULTS

We found that 24 of the screened markers positively labeled coral cells and 16 differentiated cell sub-populations. We identified 12 different cellular sub-populations using three markers, and found that each sub-population is primarily homogeneous. Lastly, we verified this technique in a sea anemone, Aiptasia pallida, and found that with minor modifications, a similar gating strategy can be successfully applied. Additionally, within A. pallida, we show elevated phagocytosis of sorted cells based on an immune associated marker.

CONCLUSIONS

In this study, we successfully adapted FACS for isolating coral cell populations and conclude that this technique is translatable for future use in other species. This technique has the potential to be used for different types of studies on the cellular stress response and other immunological studies.

Membrane transport in the malaria parasite and its host erythrocyte

As it grows and replicates within the erythrocytes of its host the malaria parasite takes up nutrients from the extracellular medium, exports metabolites and maintains a tight control over its internal ionic composition. These functions are achieved via membrane transport proteins, integral membrane proteins that mediate the passage of solutes across the various membranes that separate the biochemical machinery of the parasite from the extracellular environment. Proteins of this type play a key role in antimalarial drug resistance, as well as being candidate drug targets in their own right. This review provides an overview of recent work on the membrane transport biology of the malaria parasite-infected erythrocyte, encompassing both the parasite-induced changes in the membrane transport properties of the host erythrocyte and the cell physiology of the intracellular parasite itself.