SAS-4 Protein in Trypanosoma brucei Controls Life Cycle Transitions by Modulating the Length of the Flagellum Attachment Zone Filament

Huiqing Hu,Qing Zhou,Ziyin Li

doi:10.1074/jbc.m115.694109

Abstract

The evolutionarily conserved centriole/basal body protein SAS-4 regulates centriole duplication in metazoa and basal body duplication in flagellated and ciliated organisms. Here, we report that the SAS-4 homolog in the flagellated protozoan Trypanosoma brucei, TbSAS-4, plays an unusual role in controlling life cycle transitions by regulating the length of the flagellum attachment zone (FAZ) filament, a specialized cytoskeletal structure required for flagellum adhesion and cell morphogenesis. TbSAS-4 is concentrated at the distal tip of the FAZ filament, and depletion of TbSAS-4 in the trypomastigote form disrupts the elongation of the new FAZ filament, generating cells with a shorter FAZ associated with a longer unattached flagellum and repositioned kinetoplast and basal body, reminiscent of epimastigote-like morphology. Further, we show that TbSAS-4 associates with six additional FAZ tip proteins, and depletion of TbSAS-4 disrupts the enrichment of these FAZ tip proteins at the new FAZ tip, suggesting a role of TbSAS-4 in maintaining the integrity of this FAZ tip protein complex. Together, these results uncover a novel function of TbSAS-4 in regulating the length of the FAZ filament to control basal body positioning and life cycle transitions in T. brucei.

Highlights

Trypanosoma brucei, a flagellated protozoan and the causative agent of human sleeping sickness, does not have centrosomes, but it possesses the basal body as its microtubule-orga
The T. brucei SAS-4 Homolog Is Concentrated at the Distal Tip of the flagellum attachment zone (FAZ) Filament—Previous comprehensive analyses of centriole/basal body components conserved in eukaryotes [1, 37] showed that the T. brucei genome encodes a conserved SAS-4 homolog (Tb927.11.3300), which we named TbSAS-4, but the function of TbSAS-4 is unknown
Control and TbSAS-4 RNAi cells were co-immunostained with anti-TbSAS-6, which stains the mature basal body and the probasal body, and YL

Summary

Introduction

Trypanosoma brucei, a flagellated protozoan and the causative agent of human sleeping sickness, does not have centrosomes, but it possesses the basal body as its microtubule-orga-. We immunostained the control and TbSAS-4 RNAi cells with anti-CC2D antibody [12], the 1B41 antibody [34], and the L8C4 (anti-PFR2) antibody [33] to label the FAZ filament, the FAZ-associating quartet microtubules, and the flagellum, respectively (Fig. 3, A and B).

Results

Conclusion