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Characterization of trafficking pathways and membrane genesis in malaria-infected erythrocytes
B Pouvelle1, J A Gormley, T F Taraschi
1Department of Pathology and Cell Biology, Jefferson Medical College, Philadelphia, PA 19107.
Abstract:
The origin of membraneous structures in the cytoplasm of human erythrocytes infected with the malaria parasite, Plasmodium falciparum, was determined by confocal fluorescence imaging microscopy. When infectious merozoites invaded erythrocytes labeled with the fluorescent, lipophilic, non-exchangeable molecules DiIC16 or DiOC16, a ring of fluorescence was observed surrounding the internal parasite, indicating that the parasitophorous vacuolar membrane (PVM) is formed in part from the erythrocyte membrane. As the parasites matured, fluorescent vesicles were seen to be exported into the erythrocyte cytoplasm, beginning at 6 h post-invasion. During intraerythrocytic development, these dyes were transferred from the PVM to the parasite. When fluorescently labeled merozoites were released from these cells and invaded unlabeled erythrocytes, fluorescence was confined to the parasite throughout the entire erythrocytic cycle. Taken together, these results demonstrate that all vesicles/membranous compartments in the erythrocyte cytoplasm of parasitized erythrocytes (IRBC) contain membrane derived from the PVM. Based on this information, we define pathways that the parasite utilizes to export proteins and lipids to the host cell cytoplasm and surface membrane. When IRBC were labeled post-invasion with DiIC16 or DiOC16 and the parasites allowed to mature for one life cycle, the dyes were confined to the erythrocyte membrane, demonstrating that the host cell membrane of IRBC does not endocytose and there is no membrane exchange from the erythrocyte to the parasite. This investigation helps to resolve two long-standing controversies and provides new insights into the transport pathways that malaria parasites utilize during their development within host erythrocytes.
Insights
The malaria parasite Plasmodium falciparum forms essential membranes from the host erythrocyte membrane. These membranes are then trafficked within infected red blood cells, revealing parasite transport pathways.
Area of Science:
- Cell Biology
- Parasitology
- Malaria Research
Background:
- Human erythrocytes are infected by the malaria parasite Plasmodium falciparum.
- Understanding membrane dynamics during infection is crucial for malaria treatment.
- The origin of membranous structures within infected erythrocytes remains debated.
Purpose of the Study:
- To determine the origin of cytoplasmic membraneous structures in Plasmodium falciparum-infected human erythrocytes.
- To elucidate the pathways utilized by the parasite for protein and lipid export.
- To resolve controversies regarding membrane exchange between the host cell and parasite.
Main Methods:
- Confocal fluorescence imaging microscopy was employed.
- Lipophilic, non-exchangeable fluorescent dyes (DiIC16, DiOC16) were used to label membranes.
- Infected erythrocytes and merozoites were tracked throughout the intraerythrocytic cycle.
Main Results:
- The parasitophorous vacuolar membrane (PVM) is partially formed from the erythrocyte membrane.
- Fluorescent vesicles exported from the PVM into the erythrocyte cytoplasm were observed.
- Dyes transferred from the PVM to the parasite during development.
- Host cell membrane does not undergo endocytosis; no membrane exchange occurs from erythrocyte to parasite.
- All cytoplasmic vesicles in infected erythrocytes originate from the PVM.
Conclusions:
- The PVM serves as a source for cytoplasmic membranous compartments in infected erythrocytes.
- Defines pathways for parasite protein and lipid export to the host cell.
- Resolves long-standing questions about membrane trafficking and host-parasite interactions in malaria.