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The Plasmodium berghei Ca(2+)/H(+) exchanger, PbCAX, is essential for tolerance to environmental Ca(2+) during sexual development.

Guttery DS, Pittman JK, Frénal K, Poulin B, McFarlane LR, Slavic K, Wheatley SP, Soldati-Favre D, Krishna S, Tewari R, Staines HM - PLoS Pathog. (2013)

Bottom Line: Furthermore, genetically disrupted parasites failed to develop further from "round" form zygotes, suggesting that PbCAX is essential for ookinete development and differentiation.Therefore, PbCAX provides a mechanism for free living parasites to multiply within the ionic microenvironment of the mosquito midgut.Ca(2+) homeostasis mediated by PbCAX is critical and suggests plasmodial CAXs may be targeted in approaches designed to block parasite transmission.

View Article: PubMed Central - PubMed

Affiliation: Centre for Genetics and Genomics, School of Biology, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom.

ABSTRACT
Ca(2+) contributes to a myriad of important cellular processes in all organisms, including the apicomplexans, Plasmodium and Toxoplasma. Due to its varied and essential roles, free Ca(2+) is tightly regulated by complex mechanisms. These mechanisms are therefore of interest as putative drug targets. One pathway in Ca(2+) homeostatic control in apicomplexans uses a Ca(2+)/H(+) exchanger (a member of the cation exchanger family, CAX). The P. falciparum CAX (PfCAX) has recently been characterised in asexual blood stage parasites. To determine the physiological importance of apicomplexan CAXs, tagging and knock-out strategies were undertaken in the genetically tractable T. gondii and P. berghei parasites. In addition, a yeast heterologous expression system was used to study the function of apicomplexan CAXs. Tagging of T. gondii and P. berghei CAXs (TgCAX and PbCAX) under control of their endogenous promoters could not demonstrate measureable expression of either CAX in tachyzoites and asexual blood stages, respectively. These results were consistent with the ability of parasites to tolerate knock-outs of the genes for TgCAX and PbCAX at these developmental stages. In contrast, PbCAX expression was detectable during sexual stages of development in female gametocytes/gametes, zygotes and ookinetes, where it was dispersed in membranous networks within the cytosol (with minimal mitochondrial localisation). Furthermore, genetically disrupted parasites failed to develop further from "round" form zygotes, suggesting that PbCAX is essential for ookinete development and differentiation. This impeded phenotype could be rescued by removal of extracellular Ca(2+). Therefore, PbCAX provides a mechanism for free living parasites to multiply within the ionic microenvironment of the mosquito midgut. Ca(2+) homeostasis mediated by PbCAX is critical and suggests plasmodial CAXs may be targeted in approaches designed to block parasite transmission.

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Δpbcax parasite phenotype.(A) Bar graph illustrating exflagellation in wild-type (WT) and Δpbcax cl9 parasites. Exflagellation is presented as the numbers of exflagellation centres in 8 fields of view (magnification, ×40). Bars represent the mean ± SEM of 3 independent experiments. (B) Bar graph illustrating ookinete conversion in wild-type (WT or WT GFP) and Δpbcax cl9 and cl5 gfp parasites. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3–4 independent experiments except for WT GFP, where the bar represents the mean ± range (n = 2). (C) Ookinete conversion after crossing Δpbcax cl9 parasites with female-defective nek2 and nek4 mutants (Δpbnek2/4) and a male-defective map2 mutant (Δpbmap2). Wild-type parasites (WT) were used as a control. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3 independent experiments. (D) Bar graph illustrating the mean ± SEM numbers of oocysts per midgut (20 analysed) of wild-type (WT or WT GFP) and either Δpbcax cl9 or cl5 gfp infected mosquitoes in three independent experiments.
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ppat-1003191-g005: Δpbcax parasite phenotype.(A) Bar graph illustrating exflagellation in wild-type (WT) and Δpbcax cl9 parasites. Exflagellation is presented as the numbers of exflagellation centres in 8 fields of view (magnification, ×40). Bars represent the mean ± SEM of 3 independent experiments. (B) Bar graph illustrating ookinete conversion in wild-type (WT or WT GFP) and Δpbcax cl9 and cl5 gfp parasites. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3–4 independent experiments except for WT GFP, where the bar represents the mean ± range (n = 2). (C) Ookinete conversion after crossing Δpbcax cl9 parasites with female-defective nek2 and nek4 mutants (Δpbnek2/4) and a male-defective map2 mutant (Δpbmap2). Wild-type parasites (WT) were used as a control. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3 independent experiments. (D) Bar graph illustrating the mean ± SEM numbers of oocysts per midgut (20 analysed) of wild-type (WT or WT GFP) and either Δpbcax cl9 or cl5 gfp infected mosquitoes in three independent experiments.

Mentions: Next, the in vitro sexual development of mutant parasite clones was studied [19]. Firstly, the ability of male gametocytes to undergo exflagellation was tested by adding gametocyte containing blood to “activation” ookinete medium (see Methods and Materials) and counting exflagellation centres. Figure 5A presents data, using cl9 Δpbcax parasites, in which no statistical difference was determined between the number of exflagellation centres produced by wild-type parasites compared with the mutant line (8.4±0.6 versus 9.5±0.3; mean ± SEM; n = 3; p = 0.2, unpaired, two-tailed Student's t-test). Apparently normal exflagellation was also observed for cl5 gfp Δpbcax parasites (not tested quantitatively).


The Plasmodium berghei Ca(2+)/H(+) exchanger, PbCAX, is essential for tolerance to environmental Ca(2+) during sexual development.

Guttery DS, Pittman JK, Frénal K, Poulin B, McFarlane LR, Slavic K, Wheatley SP, Soldati-Favre D, Krishna S, Tewari R, Staines HM - PLoS Pathog. (2013)

Δpbcax parasite phenotype.(A) Bar graph illustrating exflagellation in wild-type (WT) and Δpbcax cl9 parasites. Exflagellation is presented as the numbers of exflagellation centres in 8 fields of view (magnification, ×40). Bars represent the mean ± SEM of 3 independent experiments. (B) Bar graph illustrating ookinete conversion in wild-type (WT or WT GFP) and Δpbcax cl9 and cl5 gfp parasites. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3–4 independent experiments except for WT GFP, where the bar represents the mean ± range (n = 2). (C) Ookinete conversion after crossing Δpbcax cl9 parasites with female-defective nek2 and nek4 mutants (Δpbnek2/4) and a male-defective map2 mutant (Δpbmap2). Wild-type parasites (WT) were used as a control. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3 independent experiments. (D) Bar graph illustrating the mean ± SEM numbers of oocysts per midgut (20 analysed) of wild-type (WT or WT GFP) and either Δpbcax cl9 or cl5 gfp infected mosquitoes in three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

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ppat-1003191-g005: Δpbcax parasite phenotype.(A) Bar graph illustrating exflagellation in wild-type (WT) and Δpbcax cl9 parasites. Exflagellation is presented as the numbers of exflagellation centres in 8 fields of view (magnification, ×40). Bars represent the mean ± SEM of 3 independent experiments. (B) Bar graph illustrating ookinete conversion in wild-type (WT or WT GFP) and Δpbcax cl9 and cl5 gfp parasites. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3–4 independent experiments except for WT GFP, where the bar represents the mean ± range (n = 2). (C) Ookinete conversion after crossing Δpbcax cl9 parasites with female-defective nek2 and nek4 mutants (Δpbnek2/4) and a male-defective map2 mutant (Δpbmap2). Wild-type parasites (WT) were used as a control. The conversion rate is the percentage of P28-positive parasites that had successfully differentiated into elongated ‘banana-shaped’ ookinetes. Bars represent the mean ± SEM of 3 independent experiments. (D) Bar graph illustrating the mean ± SEM numbers of oocysts per midgut (20 analysed) of wild-type (WT or WT GFP) and either Δpbcax cl9 or cl5 gfp infected mosquitoes in three independent experiments.
Mentions: Next, the in vitro sexual development of mutant parasite clones was studied [19]. Firstly, the ability of male gametocytes to undergo exflagellation was tested by adding gametocyte containing blood to “activation” ookinete medium (see Methods and Materials) and counting exflagellation centres. Figure 5A presents data, using cl9 Δpbcax parasites, in which no statistical difference was determined between the number of exflagellation centres produced by wild-type parasites compared with the mutant line (8.4±0.6 versus 9.5±0.3; mean ± SEM; n = 3; p = 0.2, unpaired, two-tailed Student's t-test). Apparently normal exflagellation was also observed for cl5 gfp Δpbcax parasites (not tested quantitatively).

Bottom Line: Furthermore, genetically disrupted parasites failed to develop further from "round" form zygotes, suggesting that PbCAX is essential for ookinete development and differentiation.Therefore, PbCAX provides a mechanism for free living parasites to multiply within the ionic microenvironment of the mosquito midgut.Ca(2+) homeostasis mediated by PbCAX is critical and suggests plasmodial CAXs may be targeted in approaches designed to block parasite transmission.

View Article: PubMed Central - PubMed

Affiliation: Centre for Genetics and Genomics, School of Biology, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom.

ABSTRACT
Ca(2+) contributes to a myriad of important cellular processes in all organisms, including the apicomplexans, Plasmodium and Toxoplasma. Due to its varied and essential roles, free Ca(2+) is tightly regulated by complex mechanisms. These mechanisms are therefore of interest as putative drug targets. One pathway in Ca(2+) homeostatic control in apicomplexans uses a Ca(2+)/H(+) exchanger (a member of the cation exchanger family, CAX). The P. falciparum CAX (PfCAX) has recently been characterised in asexual blood stage parasites. To determine the physiological importance of apicomplexan CAXs, tagging and knock-out strategies were undertaken in the genetically tractable T. gondii and P. berghei parasites. In addition, a yeast heterologous expression system was used to study the function of apicomplexan CAXs. Tagging of T. gondii and P. berghei CAXs (TgCAX and PbCAX) under control of their endogenous promoters could not demonstrate measureable expression of either CAX in tachyzoites and asexual blood stages, respectively. These results were consistent with the ability of parasites to tolerate knock-outs of the genes for TgCAX and PbCAX at these developmental stages. In contrast, PbCAX expression was detectable during sexual stages of development in female gametocytes/gametes, zygotes and ookinetes, where it was dispersed in membranous networks within the cytosol (with minimal mitochondrial localisation). Furthermore, genetically disrupted parasites failed to develop further from "round" form zygotes, suggesting that PbCAX is essential for ookinete development and differentiation. This impeded phenotype could be rescued by removal of extracellular Ca(2+). Therefore, PbCAX provides a mechanism for free living parasites to multiply within the ionic microenvironment of the mosquito midgut. Ca(2+) homeostasis mediated by PbCAX is critical and suggests plasmodial CAXs may be targeted in approaches designed to block parasite transmission.

Show MeSH
Related in: MedlinePlus