Flagellum elongation is required for correct structure, orientation and function of the flagellar pocket in Trypanosoma brucei

153

SummaryTrypanosoma brucei, a flagellated protozoan parasite causing human sleeping sickness, relies on a subpellicular microtubule array for maintenance of cell morphology. The flagellum is attached to the cell body through a poorly understood flagellum attachment zone (FAZ), and regulates cell morphogenesis using an unknown mechanism. Here we identified a new FAZ component, CC2D, which contains coiled-coil motifs followed by a C-terminal C2 domain. T. brucei CC2D is present on the FAZ filament, FAZ-juxtaposed ER membrane and the basal bodies. Depletion of CC2D inhibits the assembly of a new FAZ filament, forming a FAZ stub with a relatively fixed size at the base of a detached, but otherwise normal, flagellum. Inhibition of new FAZ formation perturbs subpellicular microtubule organization and generates short daughter cells. The cell length shows a strong linear correlation with FAZ length, in both control cells and in cells with inhibited FAZ assembly. Together, our data support a direct function of FAZ assembly in determining new daughter cell length by regulating subpellicular microtubule synthesis.

Section: Discussionmentioning

confidence: 99%

A coiled-coil- and C2-domain-containing protein is required for FAZ assembly and cell morphology in Trypanosoma brucei

Zhou

Liu

Sun

et al. 2011

153

“…The first stage of this process is maturation of the probasal body, which gains the capacity to nucleate a new flagellum (Lacomble et al, 2010). This maturation can be tracked with antibodies against trypanosome basal body component (TBBC) protein, a coiled coil protein shown to associate selectively with mature basal bodies (Dilbeck et al, 1999;Absalon et al, 2008). After maturation, the two basal bodies assemble new probasal bodies, completing the duplication cycle (Sherwin and Gull, 1989).…”

Section: Tbplk Depletion Does Not Affect Basal Body Duplication or Mamentioning

confidence: 99%

Polo-like kinase is necessary for flagellum inheritance in Trypanosoma brucei

Ikeda¹,

Graffenried²

2012

SummaryPolo-like kinases play an important role in a variety of mitotic events in mammalian cells, ranging from centriole separation and chromosome congression to abscission. To fulfill these roles, Polo-like kinase homologs move to different cellular locations as the cell cycle progresses, starting at the centrosome, progressing to the spindle poles and then the midbody. In the protist parasite Trypanosoma brucei, the single polo-like kinase homolog T. brucei PLK (TbPLK) is essential for cytokinesis and is necessary for the correct duplication of a centrin-containing cytoskeletal structure known as the bilobe. We show that TbPLK has a dynamic localization pattern during the cell cycle. The kinase localizes to the basal body, which nucleates the flagellum, and then successively localizes to a series of cytoskeletal structures that regulate the position and attachment of the flagellum to the cell body. The kinase localizes to each of these structures as they are duplicating. TbPLK associates with a specialized set of microtubules, known as the microtubule quartet, which might transport the kinase during its migration. Depletion of TbPLK causes defects in basal body segregation and blocks the duplication of the regulators that position the flagellum, suggesting that its presence on these structures might be necessary for their proper biogenesis. TbPLK migrates throughout the cell in T. brucei, but the specific locations to which it targets and its functions are geared towards the inheritance of a properly positioned and attached flagellum.

“…In intraflagellar transport mutants, where the growth of a new axoneme is prevented, basal body segregation still occurs to some extent (Absalon et al, 2008;Davidge et al, 2006). Indeed, after segregation, a flagellar sleeve representing an 'empty' new flagellum lies on the correct posterior side of the old flagellum (Davidge et al, 2006).…”

Section: Basal Body Migration and Cell Morphogenesismentioning

confidence: 99%

Basal body movements orchestrate membrane organelle division and cell morphogenesis inTrypanosoma brucei

Lacomble

Vaughan

Gadelha

et al. 2010

144

SummaryThe defined shape and single-copy organelles of Trypanosoma brucei mean that it provides an excellent model in which to study how duplication and segregation of organelles is interfaced with morphogenesis of overall cell shape and form. The centriole or basal body of eukaryotic cells is often seen to be at the centre of such processes. We have used a combination of electron microscopy and electron tomography techniques to provide a detailed three-dimensional view of duplication of the basal body in trypanosomes. We show that the basal body duplication and maturation cycle exerts an influence on the intimately associated flagellar pocket membrane system that is the portal for secretion and uptake from this cell. At the start of the cell cycle, a probasal body is positioned anterior to the basal body of the existing flagellum. At the G1-S transition, the probasal body matures, elongates and invades the pre-existing flagellar pocket to form the new flagellar axoneme. The new basal body undergoes a spectacular anti-clockwise rotation around the old flagellum, while its short new axoneme is associated with the pre-existing flagellar pocket. This rotation and subsequent posterior movements results in division of the flagellar pocket and ultimately sets parameters for subsequent daughter cell morphogenesis.