Abstract
Aurora B kinase plays essential roles in mitosis and cytokinesis in eukaryotes. In the procyclic form of Trypanosoma brucei, the Aurora B homolog TbAUK1 regulates mitosis and cytokinesis, phosphorylates the Tousled-like kinase TbTLK1, interacts with two mitotic kinesins TbKIN-A and TbKIN-B and forms a novel chromosomal passenger complex (CPC) with two novel proteins TbCPC1 and TbCPC2. Here we show with time-lapse video microscopy the time course of CPC trans-localization from the spindle midzone in late anaphase to the dorsal side of the cell where the anterior end of daughter cell is tethered, and followed by a glide toward the posterior end to divide the cell, representing a novel mode of cytokinesis in eukaryotes. The three subunits of CPC, TbKIN-B and TbTLK1 interact with one another suggesting a close association among the five proteins. An ablation of TbTLK1 inhibited the subsequent trans-localization of CPC and TbKIN-B, whereas a knockdown of CPC or TbKIN-B disrupted the spindle pole localization of TbTLK1 during mitosis. In the bloodstream form of T. brucei, the five proteins also play essential roles in chromosome segregation and cytokinesis and display subcellular localization patterns similar to that in the procyclic form. The CPC in bloodstream form also undergoes a trans-localization during cytokinesis similar to that in the procyclic form. All together, our results indicate that the five-protein complex CPC-TbTLK1-TbKIN-B plays key roles in regulating chromosome segregation in the early phase of mitosis and that the highly unusual mode of cytokinesis mediated by CPC occurs in both forms of trypanosomes.
Highlights
IntroductionIn the bloodstream form, inhibition of mitosis prevents cytokinesis, but not additional rounds of G1 re-entry and organelle replication resulting in giant polyploid cells with multiple kinetoplasts, basal bodies and flagella [5,6,7,8,9]
Trypanosoma brucei is an ancient unicellular protozoan parasite that causes sleeping sickness in human and nagana in cattle in subSahara Africa
We found that when TbTLK1 was fused to the Gal4 activation domain, it binds to TbCPC1 and TbAUK1 with strong affinity and to TbCPC2 and TbKIN-B with somewhat weaker affinity, but it does not bind to TbKIN-A (Fig. 2A)
Summary
In the bloodstream form, inhibition of mitosis prevents cytokinesis, but not additional rounds of G1 re-entry and organelle replication resulting in giant polyploid cells with multiple kinetoplasts, basal bodies and flagella [5,6,7,8,9]. It suggests that the procyclic form, but not the bloodstream form, lacks the checkpoint linking mitosis to cytokinesis, whereas the bloodstream form lacks a spindle assembly checkpoint. The molecular mechanisms behind these distinctions remain unclear at present and represent intriguing phenomena for further pursuit
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