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Biogenesis of the trypanosome endo-exocytotic organelle is cytoskeleton mediated.

Bonhivers M, Nowacki S, Landrein N, Robinson DR - PLoS Biol. (2008)

Bottom Line: Remarkably, RNA interference (RNAi)-mediated ablation of BILBO1 in insect procyclic-form parasites prevents FP biogenesis and induces vesicle accumulation, Golgi swelling, the aberrant repositioning of the new flagellum, and cell death.Cultured bloodstream-form parasites are also nonviable when subjected to BILBO1 RNAi.These results provide the first molecular evidence for cytoskeletally mediated FP biogenesis.

View Article: PubMed Central - PubMed

Affiliation: Microbiologie Cellulaire et Moléculaire et Pathogénicité, UMR-CNRS 5234, University Bordeaux 2, Bordeaux, Cedex France.

ABSTRACT
Trypanosoma brucei is a protozoan parasite that is used as a model organism to study such biological phenomena as gene expression, protein trafficking, and cytoskeletal biogenesis. In T. brucei, endocytosis and exocytosis occur exclusively through a sequestered organelle called the flagellar pocket (FP), an invagination of the pellicular membrane. The pocket is the sole site for specific receptors thus maintaining them inaccessible to components of the innate immune system of the mammalian host. The FP is also responsible for the sorting of protective parasite glycoproteins targeted to, or recycling from, the pellicular membrane, and for the removal of host antibodies from the cell surface. Here, we describe the first characterisation of a flagellar pocket cytoskeletal protein, BILBO1. BILBO1 functions to form a cytoskeleton framework upon which the FP is made and which is also required and essential for FP biogenesis and cell survival. Remarkably, RNA interference (RNAi)-mediated ablation of BILBO1 in insect procyclic-form parasites prevents FP biogenesis and induces vesicle accumulation, Golgi swelling, the aberrant repositioning of the new flagellum, and cell death. Cultured bloodstream-form parasites are also nonviable when subjected to BILBO1 RNAi. These results provide the first molecular evidence for cytoskeletally mediated FP biogenesis.

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Related in: MedlinePlus

A Schematic Diagram That Describes the Normal Procyclic T. brucei Cell Division Cycle and the Fate of Induced BILBO1 RNAi CellsThis schematic shows the organisation of the flagellum, function of the FP, and location of the FPC in a WT cell (A). The lower half of (A) illustrates the normal division cycle of the FP, Golgi, and flagellum in WT cells, whereas the drastically altered morphology of an induced BILBO1 RNAi cell (B) shows the absence of a FP and the loss of new flagellum-to-cell body attachment. The lower half of (B) shows an example of the major phenotype formed resulting from BILBO1 RNAi knockdown in procyclic cells. BILBO1 RNAi prevents FPC and FP biogenesis, disrupts endo-exocytosis, initiates cytokinesis block, and induces new flagellum cell body detachment and relocation to the posterior of the cell.
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pbio-0060105-g007: A Schematic Diagram That Describes the Normal Procyclic T. brucei Cell Division Cycle and the Fate of Induced BILBO1 RNAi CellsThis schematic shows the organisation of the flagellum, function of the FP, and location of the FPC in a WT cell (A). The lower half of (A) illustrates the normal division cycle of the FP, Golgi, and flagellum in WT cells, whereas the drastically altered morphology of an induced BILBO1 RNAi cell (B) shows the absence of a FP and the loss of new flagellum-to-cell body attachment. The lower half of (B) shows an example of the major phenotype formed resulting from BILBO1 RNAi knockdown in procyclic cells. BILBO1 RNAi prevents FPC and FP biogenesis, disrupts endo-exocytosis, initiates cytokinesis block, and induces new flagellum cell body detachment and relocation to the posterior of the cell.

Mentions: The FPC remains intact and attached to flagella after detergent and salt extraction. The FPC thus most likely consists of a complex of proteins in addition to BILBO1, because BILBO1 itself does not appear to have any obvious membrane-targeting domains, but it does have a large coiled-coil domain consistent with protein–protein interactions. One function of the FPC complex is to physically link the flagellum to the neck of the FP and the cell body. More precisely, this link would produce an intimate bridge between the FP membrane, pellicular membrane, and the flagellum membrane. This bridge complex forms a barrier or an adherens junction-like plaque between the flagellum and the subpellicular cytoskeleton. It is well documented that the trypanosome axoneme exits the FP via the FPC, but little data have been published on the organisation of this structure. It follows that structural homologs are likely to be present in many organisms in order to define and localise the exit site of cilia or axonemes. A schematic diagram of the positioning of the FPC and its role in noninduced or induced cells is shown in Figure 7. This figure also illustrates the distribution and organisation of organelles before and after BILBO1 RNAi knockdown.


Biogenesis of the trypanosome endo-exocytotic organelle is cytoskeleton mediated.

Bonhivers M, Nowacki S, Landrein N, Robinson DR - PLoS Biol. (2008)

A Schematic Diagram That Describes the Normal Procyclic T. brucei Cell Division Cycle and the Fate of Induced BILBO1 RNAi CellsThis schematic shows the organisation of the flagellum, function of the FP, and location of the FPC in a WT cell (A). The lower half of (A) illustrates the normal division cycle of the FP, Golgi, and flagellum in WT cells, whereas the drastically altered morphology of an induced BILBO1 RNAi cell (B) shows the absence of a FP and the loss of new flagellum-to-cell body attachment. The lower half of (B) shows an example of the major phenotype formed resulting from BILBO1 RNAi knockdown in procyclic cells. BILBO1 RNAi prevents FPC and FP biogenesis, disrupts endo-exocytosis, initiates cytokinesis block, and induces new flagellum cell body detachment and relocation to the posterior of the cell.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2365980&req=5

pbio-0060105-g007: A Schematic Diagram That Describes the Normal Procyclic T. brucei Cell Division Cycle and the Fate of Induced BILBO1 RNAi CellsThis schematic shows the organisation of the flagellum, function of the FP, and location of the FPC in a WT cell (A). The lower half of (A) illustrates the normal division cycle of the FP, Golgi, and flagellum in WT cells, whereas the drastically altered morphology of an induced BILBO1 RNAi cell (B) shows the absence of a FP and the loss of new flagellum-to-cell body attachment. The lower half of (B) shows an example of the major phenotype formed resulting from BILBO1 RNAi knockdown in procyclic cells. BILBO1 RNAi prevents FPC and FP biogenesis, disrupts endo-exocytosis, initiates cytokinesis block, and induces new flagellum cell body detachment and relocation to the posterior of the cell.
Mentions: The FPC remains intact and attached to flagella after detergent and salt extraction. The FPC thus most likely consists of a complex of proteins in addition to BILBO1, because BILBO1 itself does not appear to have any obvious membrane-targeting domains, but it does have a large coiled-coil domain consistent with protein–protein interactions. One function of the FPC complex is to physically link the flagellum to the neck of the FP and the cell body. More precisely, this link would produce an intimate bridge between the FP membrane, pellicular membrane, and the flagellum membrane. This bridge complex forms a barrier or an adherens junction-like plaque between the flagellum and the subpellicular cytoskeleton. It is well documented that the trypanosome axoneme exits the FP via the FPC, but little data have been published on the organisation of this structure. It follows that structural homologs are likely to be present in many organisms in order to define and localise the exit site of cilia or axonemes. A schematic diagram of the positioning of the FPC and its role in noninduced or induced cells is shown in Figure 7. This figure also illustrates the distribution and organisation of organelles before and after BILBO1 RNAi knockdown.

Bottom Line: Remarkably, RNA interference (RNAi)-mediated ablation of BILBO1 in insect procyclic-form parasites prevents FP biogenesis and induces vesicle accumulation, Golgi swelling, the aberrant repositioning of the new flagellum, and cell death.Cultured bloodstream-form parasites are also nonviable when subjected to BILBO1 RNAi.These results provide the first molecular evidence for cytoskeletally mediated FP biogenesis.

View Article: PubMed Central - PubMed

Affiliation: Microbiologie Cellulaire et Moléculaire et Pathogénicité, UMR-CNRS 5234, University Bordeaux 2, Bordeaux, Cedex France.

ABSTRACT
Trypanosoma brucei is a protozoan parasite that is used as a model organism to study such biological phenomena as gene expression, protein trafficking, and cytoskeletal biogenesis. In T. brucei, endocytosis and exocytosis occur exclusively through a sequestered organelle called the flagellar pocket (FP), an invagination of the pellicular membrane. The pocket is the sole site for specific receptors thus maintaining them inaccessible to components of the innate immune system of the mammalian host. The FP is also responsible for the sorting of protective parasite glycoproteins targeted to, or recycling from, the pellicular membrane, and for the removal of host antibodies from the cell surface. Here, we describe the first characterisation of a flagellar pocket cytoskeletal protein, BILBO1. BILBO1 functions to form a cytoskeleton framework upon which the FP is made and which is also required and essential for FP biogenesis and cell survival. Remarkably, RNA interference (RNAi)-mediated ablation of BILBO1 in insect procyclic-form parasites prevents FP biogenesis and induces vesicle accumulation, Golgi swelling, the aberrant repositioning of the new flagellum, and cell death. Cultured bloodstream-form parasites are also nonviable when subjected to BILBO1 RNAi. These results provide the first molecular evidence for cytoskeletally mediated FP biogenesis.

Show MeSH
Related in: MedlinePlus