Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
* Author for correspondence (e-mail: keith.gull{at}path.ox.ac.uk)
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Introduction |
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Flagellum functions: morphogenesis to pathogenicity |
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The trypanosome flagellum is now recognized as a major contributor to
pathogenicity of these parasites. In this context, it contributes motility
functions important in moving both the trypanosome and surface molecules,
sensory recognition of the host/vector environment and, finally, recognition
and attachment necessary for immobilizing the parasite at vector surfaces at
certain critical life-cycle stages (Borst
and Fairlamb, 1998; Gull,
1999
).
The intrinsic feature of the trypanosome flagellum is that the existing
flagellum is maintained and a new flagellum is produced during each cell
cycle. Given that many of the trypanosome organelles exist as single copies,
the basic issue facing the cell is a problem of coordinated duplication and
segregation of structures and organelles, some in a conservative and some in a
semi-conservative manner (Gull,
1999).
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Flagellum structure |
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The flagellum and cell morphogenesis |
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Essentially three processes encapsulate the morphological events involved
in cell proliferation and cell differentiation in T. brucei
duplication, positioning and segregation. The earliest morphological events in
cell proliferation occur with duplication of the basal bodies, formation of
the new flagellum and other connected cytoskeletal elements. The precise
duplication and positioning of these cytoskeletal elements are crucial to
ensure correct segregation to the two daughter cells
(Gull, 1999). These early
events occur in a strict temporal order and are coordinated with the periodic
kinetoplast S-phase to ensure that the duplicated mitochondrial genome is
connected to the duplicated basal bodies, securing its inheritance and
segregation to the two new daughter cells
(Robinson and Gull, 1991
).
Once duplication and positioning of the new flagellum and connected
elements are achieved, the process of building a new subpellicular array of
microtubules begins. This occurs by the insertion of new microtubules between
old microtubules, such that the complex is segregated semi-conservatively to
each daughter trypanosome (Sherwin and
Gull, 1989b). Details of these events vary slightly between the
bloodstream and vector forms of the parasite. The details below, poster and
movie (see
http://jcs.biologists.org/supplemental)
describe the events of the procyclic (tsetse midgut) form of the parasite.
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Spatial patterning and the flagellum |
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Spatial organisation is an important aspect to our understanding of many cellular processes that are of interest to cell biologists (e.g. mitotic spindle assembly/disassembly, cell division, centrosome duplication and cell polarity). The complexity of cytoskeletal construction and remodelling within the confines of the intact cytoskeleton of T. brucei is an example of the difficulties faced in attempting to understand and explain spatial organisation. Construction of the 3D spatial models in this poster and the accompanying movie resulted from a collaboration between laboratory scientists and computer graphic artists. The requirements of providing a distinct spatial blue-print to the graphic artists proved to be an excellent test of the laboratory scientist's knowledge. It led to the formulation of a number of new research programmes and highlighted the lack of real 3D detail in the descriptions of many cell biological systems. The use of new computer technology to enable 3D spatial organisation of different types of cell biological data to be documented, visualized and analysed at high resolution has increasing relevance. However, our experience is that when developed in an interactive manner, it not only facilitates visualisation of complicated events, but also highlights data limitations and enables formulation of new questions.
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Acknowledgments |
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Footnotes |
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References |
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Borst, P. and Fairlamb, A. (1998). Surface receptors and transporters of Trypanosoma brucei. Annu. Rev. Microbiol. 52,745 -778.[CrossRef][Medline]
Gull, K. (1999). The cytoskeleton of Trypanosomatid Parasites. Annu. Rev. Microbiol. 53,629 -655.[CrossRef][Medline]
Moreira-Leite, F. F., Sherwin, T., Kohl, L. and Gull, K. (2001). A trypanosome structure involved in transmitting cytoplasmic information during cell division. Science 294,601 -602.
Robinson, D. R. and Gull, K. (1991). Basal body movement as a mechanism for mitochondrial genome segregation in the trypanosome cell cycle. Nature 352,731 -734.[CrossRef][Medline]
Sherwin, T. and Gull, K. (1989a). The cell-division cycle of Trypanosoma brucei brucei timing of event markers and cytoskeletal modulation. Phil. Trans. R. Soc. London Ser B. 323,573 -588.[Medline]
Sherwin, T. and Gull, K. (1989b). Visualisation of detyrosination along single microtubules reveals novel mechanisms of assembly during cytoskeletal duplication in trypanosomes. Cell 57,211 -221.[Medline]
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