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Developmental variation in Rab11-dependent trafficking in Trypanosoma brucei
Belinda S Hall1, Emma Smith, Wolfram Langer
1Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, United Kingdom. mcf34@cam.ac.uk
Eukaryotic Cell
|May 10, 2005
Summary
The small GTPase TbRAB11 is crucial for Trypanosoma brucei viability in both mammalian and insect stages, regulating endocytosis and protein recycling with stage-specific functions.
Area of Science:
- Cell Biology
- Parasitology
- Molecular Biology
Background:
- Endocytosis in Trypanosoma brucei is developmentally regulated, with higher activity in the mammalian stage for immune evasion.
- The small GTPase TbRAB11 is highly expressed in the mammalian stage, involved in recycling GPI-anchored proteins and trafficking internalized molecules.
- The function of TbRAB11 in the procyclic (insect) stage of Trypanosoma brucei remained unassigned.
Purpose of the Study:
- To investigate the essentiality and function of TbRAB11 in both bloodstream (mammalian) and procyclic (insect) forms of Trypanosoma brucei.
- To elucidate the specific roles of TbRAB11 in endocytosis, protein trafficking, and recycling across different life stages of the parasite.
Main Methods:
- RNA interference (RNAi) was employed to suppress TbRAB11 expression in both bloodstream and procyclic forms.
- Cell morphology, flagellar pocket size, and various endocytic processes (lectin uptake, transferrin uptake/export, fluid-phase endocytosis) were analyzed.
- Localization of internalized proteins, such as VSG and transferrin, was examined in relation to TbRAB11 suppression.
Main Results:
- TbRAB11 suppression was rapidly lethal in bloodstream forms, causing cell rounding and flagellar pocket enlargement.
- In procyclic forms, TbRAB11 suppression was also lethal but slower, leading to cell rounding without affecting the flagellar pocket.
- Bloodstream forms showed inhibited transferrin export and a block in post-endosomal transport, while procyclic forms exhibited blocked fluid-phase endocytosis and surface protein internalization.
Conclusions:
- TbRAB11 is essential for the viability of Trypanosoma brucei in both life stages, demonstrating developmental stage-specific functions.
- The primary role of TbRAB11 shifts from regulating recycling and post-endosomal transport in bloodstream forms to controlling initial endocytosis in procyclic forms.
- These findings highlight the adaptability of TbRAB11-mediated pathways to the distinct physiological demands of different parasite life stages.