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A malaria membrane skeletal protein is essential for normal morphogenesis, motility, and infectivity of sporozoites.

Khater EI, Sinden RE, Dessens JT - J. Cell Biol. (2004)

Bottom Line: Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion.We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites.These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Imperail College London, London SW7 2AZ, England, UK.

ABSTRACT
Membrane skeletons are structural elements that provide mechanical support to the plasma membrane and define cell shape. Here, we identify and characterize a putative protein component of the membrane skeleton of the malaria parasite. The protein, named PbIMC1a, is the structural orthologue of the Toxoplasma gondii inner membrane complex protein 1 (TgIMC1), a component of the membrane skeleton in tachyzoites. Using targeted gene disruption in the rodent malaria species Plasmodium berghei, we show that PbIMC1a is involved in sporozoite development, is necessary for providing normal sporozoite cell shape and mechanical stability, and is essential for sporozoite infectivity in insect and vertebrate hosts. Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion. We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites. These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

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Characteristics of PbIMC1a-KO sporozoites. (A) Sporozoite shapes as observed by differential interference contrast (DIC). (B) Sporozoite shapes as observed by IFA staining for circumsporozoite protein (CSP, green) and DNA (red). (C) Western blot of oocyst sporozoites from WT and PbIMC1a-KO parasite clones 104 and 204. (D) Negative labeling of a PbIMC1a-KO sporozoite by IFA staining for PbIMC1a. (E) Cross section of sporulating oocysts. (F) Close-up view of E showing budding sporozoites. White arrowheads point at sporozoite budding sites. (G) Cross section of sporozoites. WT: wild-type, KO: PbIMC1a-KO, sb: sporoblast, sz: sporozoite, oc: oocyst wall, nu: nucleus, ap: apicoplast, mi: mitochondrion, pm: plasma membrane, imc: inner membrane complex, smt: subpellicular microtubules. Bars: 5 μm (E), 1 μm (F), 0.1 μm (G).
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fig4: Characteristics of PbIMC1a-KO sporozoites. (A) Sporozoite shapes as observed by differential interference contrast (DIC). (B) Sporozoite shapes as observed by IFA staining for circumsporozoite protein (CSP, green) and DNA (red). (C) Western blot of oocyst sporozoites from WT and PbIMC1a-KO parasite clones 104 and 204. (D) Negative labeling of a PbIMC1a-KO sporozoite by IFA staining for PbIMC1a. (E) Cross section of sporulating oocysts. (F) Close-up view of E showing budding sporozoites. White arrowheads point at sporozoite budding sites. (G) Cross section of sporozoites. WT: wild-type, KO: PbIMC1a-KO, sb: sporoblast, sz: sporozoite, oc: oocyst wall, nu: nucleus, ap: apicoplast, mi: mitochondrion, pm: plasma membrane, imc: inner membrane complex, smt: subpellicular microtubules. Bars: 5 μm (E), 1 μm (F), 0.1 μm (G).

Mentions: PbIMC1a-KO parasites developed normally in mice and were morphologically indistinguishable from WT parasites in Giemsa-stained blood films. Normal exflagellation and differentiation of gametocytes into ookinetes both in vitro and in vivo was observed (unpublished data). WT and PbIMC1a-KO parasite-infected Anopheles stephensi mosquitoes developed comparable numbers of oocysts in controlled experiments (Table I), indicating that the PbIMC1a-KO ookinetes are capable of normal midgut invasion and subsequent ookinete to oocyst transition. Oocysts in PbIMC1a-KO parasite-infected mosquitoes appeared to develop normally and formed large numbers of sporozoites (Table I). However, closer examination of these sporozoites revealed that they were of abnormal shape and some 20–30% smaller in size (Fig. 4, A and B). Each sporozoite possessed a single enlarged, protruding area associated with the position of the nucleus. The position of these protrusions varied between sporozoites from being located at the posterior end to being positioned near the middle of the sporozoite. Viability of oocyst and hemolymph sporozoites was comparable between WT and PbIMC1a-KO parasites (97–99%; n = 100), indicating that the abnormal cell shape was not the result of premature cell degeneration or death. This is supported by the fact that we did not observe sporozoites with normal morphology.


A malaria membrane skeletal protein is essential for normal morphogenesis, motility, and infectivity of sporozoites.

Khater EI, Sinden RE, Dessens JT - J. Cell Biol. (2004)

Characteristics of PbIMC1a-KO sporozoites. (A) Sporozoite shapes as observed by differential interference contrast (DIC). (B) Sporozoite shapes as observed by IFA staining for circumsporozoite protein (CSP, green) and DNA (red). (C) Western blot of oocyst sporozoites from WT and PbIMC1a-KO parasite clones 104 and 204. (D) Negative labeling of a PbIMC1a-KO sporozoite by IFA staining for PbIMC1a. (E) Cross section of sporulating oocysts. (F) Close-up view of E showing budding sporozoites. White arrowheads point at sporozoite budding sites. (G) Cross section of sporozoites. WT: wild-type, KO: PbIMC1a-KO, sb: sporoblast, sz: sporozoite, oc: oocyst wall, nu: nucleus, ap: apicoplast, mi: mitochondrion, pm: plasma membrane, imc: inner membrane complex, smt: subpellicular microtubules. Bars: 5 μm (E), 1 μm (F), 0.1 μm (G).
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Related In: Results  -  Collection

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fig4: Characteristics of PbIMC1a-KO sporozoites. (A) Sporozoite shapes as observed by differential interference contrast (DIC). (B) Sporozoite shapes as observed by IFA staining for circumsporozoite protein (CSP, green) and DNA (red). (C) Western blot of oocyst sporozoites from WT and PbIMC1a-KO parasite clones 104 and 204. (D) Negative labeling of a PbIMC1a-KO sporozoite by IFA staining for PbIMC1a. (E) Cross section of sporulating oocysts. (F) Close-up view of E showing budding sporozoites. White arrowheads point at sporozoite budding sites. (G) Cross section of sporozoites. WT: wild-type, KO: PbIMC1a-KO, sb: sporoblast, sz: sporozoite, oc: oocyst wall, nu: nucleus, ap: apicoplast, mi: mitochondrion, pm: plasma membrane, imc: inner membrane complex, smt: subpellicular microtubules. Bars: 5 μm (E), 1 μm (F), 0.1 μm (G).
Mentions: PbIMC1a-KO parasites developed normally in mice and were morphologically indistinguishable from WT parasites in Giemsa-stained blood films. Normal exflagellation and differentiation of gametocytes into ookinetes both in vitro and in vivo was observed (unpublished data). WT and PbIMC1a-KO parasite-infected Anopheles stephensi mosquitoes developed comparable numbers of oocysts in controlled experiments (Table I), indicating that the PbIMC1a-KO ookinetes are capable of normal midgut invasion and subsequent ookinete to oocyst transition. Oocysts in PbIMC1a-KO parasite-infected mosquitoes appeared to develop normally and formed large numbers of sporozoites (Table I). However, closer examination of these sporozoites revealed that they were of abnormal shape and some 20–30% smaller in size (Fig. 4, A and B). Each sporozoite possessed a single enlarged, protruding area associated with the position of the nucleus. The position of these protrusions varied between sporozoites from being located at the posterior end to being positioned near the middle of the sporozoite. Viability of oocyst and hemolymph sporozoites was comparable between WT and PbIMC1a-KO parasites (97–99%; n = 100), indicating that the abnormal cell shape was not the result of premature cell degeneration or death. This is supported by the fact that we did not observe sporozoites with normal morphology.

Bottom Line: Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion.We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites.These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Imperail College London, London SW7 2AZ, England, UK.

ABSTRACT
Membrane skeletons are structural elements that provide mechanical support to the plasma membrane and define cell shape. Here, we identify and characterize a putative protein component of the membrane skeleton of the malaria parasite. The protein, named PbIMC1a, is the structural orthologue of the Toxoplasma gondii inner membrane complex protein 1 (TgIMC1), a component of the membrane skeleton in tachyzoites. Using targeted gene disruption in the rodent malaria species Plasmodium berghei, we show that PbIMC1a is involved in sporozoite development, is necessary for providing normal sporozoite cell shape and mechanical stability, and is essential for sporozoite infectivity in insect and vertebrate hosts. Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion. We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites. These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

Show MeSH
Related in: MedlinePlus