Modulation of flagellum attachment zone protein FLAM3 and regulation of the cell shape in Trypanosoma brucei life cycle transitions.

Jack D Sunter,Julius Lukeš,Paul G Mckean,Keith Gull,Corinna Benz,Michael L Ginger,Sarah Whipple,Jane Andre

doi:10.1242/jcs.171645

Abstract

ABSTRACTThe cell shape of Trypanosoma brucei is influenced by flagellum-to-cell-body attachment through a specialised structure – the flagellum attachment zone (FAZ). T. brucei exhibits numerous morphological forms during its life cycle and, at each stage, the FAZ length varies. We have analysed FLAM3, a large protein that localises to the FAZ region within the old and new flagellum. Ablation of FLAM3 expression causes a reduction in FAZ length; however, this has remarkably different consequences in the tsetse procyclic form versus the mammalian bloodstream form. In procyclic form cells FLAM3 RNAi results in the transition to an epimastigote-like shape, whereas in bloodstream form cells a severe cytokinesis defect associated with flagellum detachment is observed. Moreover, we demonstrate that the amount of FLAM3 and its localisation is dependent on ClpGM6 expression and vice versa. This evidence demonstrates that FAZ is a key regulator of trypanosome shape, with experimental perturbations being life cycle form dependent. An evolutionary cell biology explanation suggests that these differences are a reflection of the division process, the cytoskeleton and intrinsic structural plasticity of particular life cycle forms.

Highlights

Trypanosoma brucei is a unicellular eukaryotic parasite that causes human African trypanosomiasis
To determine the localisation of FLAM3, T. brucei SMOXP9 cells with an allele of FLAM3 tagged at the N-terminus with eYFP were created. eYFP::FLAM3 localised to the flagellum and the signal partially overlapped with the paraflagellar rod, an extra-axonemal structure; eYFP::FLAM3 was not evenly distributed along the length of the flagellum (Fig. 1B)
The FLAM3 signal was stronger in the part of the flagellum that was attached to the cell body by the flagellum attachment zone (FAZ), and much reduced in the unattached flagellum that extends beyond the anterior end of the cell body (Fig. 1B)

Summary

Introduction

Trypanosoma brucei is a unicellular eukaryotic parasite that causes human African trypanosomiasis. T. brucei has a complex life cycle, with stages in both a mammalian host and insect vector, and adopts numerous different morphologies, each adapted to the ecological niche the cell is occupying at that given point in the life cycle (Matthews, 2011; Ooi and Bastin, 2013; Sharma et al, 2009). T. brucei is found either as a trypomastigote with the kinetoplast posterior to the nucleus or as an epimastigote with the kinetoplast anterior to the nucleus In both cell forms the flagellum is attached to the cell body

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Conclusion