BOH1 cooperates with Polo-like kinase to regulate flagellum inheritance and cytokinesis initiation in Trypanosoma brucei

Abstract

Trypanosoma brucei possesses a motile flagellum that determines cell morphology and the cell division plane. Inheritance of the newly assembled flagellum during the cell cycle is controlled by the Polo-like kinase homolog TbPLK, which also regulates cytokinesis initiation. How TbPLK is targeted to its subcellular locations remains poorly understood. Here we report the trypanosome-specific protein BOH1 that cooperates with TbPLK to regulate flagellum inheritance and cytokinesis initiation in the procyclic form of T. brucei. BOH1 localizes to an unusual sub-domain in the flagellum-associated hook complex, bridging the hook complex, the centrin arm and the flagellum attachment zone. Depletion of BOH1 disrupts hook-complex morphology, inhibits centrin-arm elongation and abolishes flagellum attachment zone assembly, leading to flagellum mis-positioning and detachment. Further, BOH1 deficiency impairs the localization of TbPLK and the cytokinesis regulator CIF1 to the cytokinesis initiation site, providing a molecular mechanism for its role in cytokinesis initiation. These findings reveal the roles of BOH1 in maintaining hookcomplex morphology and regulating flagellum inheritance, and establish BOH1 as an upstream regulator of the TbPLK-mediated cytokinesis regulatory pathway.

Maintenance of hook complex integrity and centrin arm assembly facilitates flagellum inheritance in Trypanosoma brucei

“…The first evidence to demonstrate the involvement of the hook complex in flagellum inheritance was obtained from the functional characterization of a hook complex-localizing protein named TbLRRP1, which showed that knockdown of TbLRRP1 abolished FAZ assembly and caused flagellum detachment (8). Further evidence to support this notion came from the study of BOH1, which localizes to the hooked part of the hook complex and maintains hook complex morphology to control flagellum inheritance (22). In the current work, we identified BOH2, which co-localizes with BOH1 to the hooked part of the hook complex, and demonstrated its essential role in flagellum inheritance, thus providing additional evidence for the involvement of the hook complex in flagellum inheritance.…”

“…This notion is supported by the distinct defects on the hook complex and the centrin arm exerted by the knockdowns of BOH1 and BOH2. Depletion of BOH1 distorted the overall morphology of the hook complex and impaired the elongation of the centrin arm (22), whereas RNAi of BOH2 disrupted the integrity of the hook complex and inhibited the formation of the centrin arm (Figs. 4 and 5).…”

“…The hooked part of the hook complex sits atop the TbBILBO1-labeled FPC and runs alongside the specialized quartet microtubules, and the shank part of the hook complex and the centrin arm flank the FAZ filament (19). Although the precise functions of the hook complex and the centrin arm remain largely unknown, functional characterizations of some hook complex-localizing proteins indicated that proteins localized to different sub-domains of the hook complex might play distinct functions (8,21,22). Knockdown of TbLRRP1 suggests that the hook complex is involved in FAZ assembly and flagellum attachment (8).…”

“…Knockdown of TbSmee1, which localizes to the shank part of the hook complex and the new FAZ tip, disrupts hook complex morphology (21). Knockdown of BOH1, which localizes to the fishhook part of the hook complex resembling a fishing bait hung on a fishhook, impairs flagellum inheritance and cytokinesis initiation (22). Through proximitydependent biotinylation (BioID) using TbMORN1 as bait (23) and proteome-wide protein localization (24), more than 50 proteins have been localized to the hook complex.…”

Gene Co-Expression Network Analysis of Trypanosoma brucei in Tsetse Fly Vector

“…2 and 3) was functionally enriched for GO terms such as DNA replication and chromosome organization, and KEGG pathway term homologous recombination indicating that its genes are involved in the progression of cell cycle (Additional le 11: Figure S5 and Table 1). Additionally, the red module has some genes involved in cytokinesis such as BOH1 (Tb927.10.12720), that cooperates with TbPLK to initiate cytokinesis and agellum inheritance [42], and Cytokinesis Initiation Factor 2 (CIF2) (Tb927.9.14290) which is involved in initiation of cytokinesis [43] (Additional le 6). Other genes assigned to this module were in concordance with the enriched functions.…”