The parasitic protozoa, Trypanosoma brucei spp., are the causative pathogens of African sleeping sickness in humans and nagana in cattle. They are a family of deeply branched eukaryotes that exhibit many unique features during their cell cycle progression. Due to the presence of a single mitochondrion in each cell, the nuclear cycle and mitochondrial cycle in T. brucei have to be coordinated for a fruitful cell division, suggesting also that cytokinesis could be controlled by either of the two cycles. Our studies indicated that cytokinesis is primarily regulated by the mitochondrion in the insect (procyclic) form but by the nucleus in the bloodstream form of T. brucei. We also observed that a block of mitosis achieves genuine mitotic arrest in the procylic form but not in the bloodstream form, which continues with re-entries into a new G1 phase and nonstop nuclear DNA synthesis. The bloodstream form is thus apparently lacking the spindle assembly checkpoint, which is present and functioning in the procyclic form. These unusual changes in command, never observed among any other eukaryotes previously, prompted us to examine some of the protein kinases in T. brucei known to control both mitosis and cytokinesis in other eukaryotes. The Polo-like kinase (TbPLK) turns out regulating only cytokinesis and localizing to the flagellum attachment zone (FAZ) in T. brucei. The Aurora-like kinase (TbAUK1) resides in a novel chromosomal passenger complex (CPC) that trans-localizes from the central spindle midzone in late anaphase across the nuclear envelope to the FAZ and then transcends down from the anterior to the posterior end along the FAZ to separate the cell into two. This is a most unusual mode of cytokinesis. We plan to pursue it further by tracing the CPC trans-localization with time-lapse imaging and dissecting the specific roles of TbPLK and TbAUK1 and their potential interactions during this fascinating process with the eventual goal of establishing the cell regulation in T. brucei a useful model system for advanced basic research as well as a potential target for anti-trypanosomiasis chemotherapy.

Public Health Relevance

African trypanosomes, the Trypanosoma brucei spp., are parasitic protozoa causing sleeping sickness in humans and nagana in cattle in Sub-Sahara Africa. They are ancient organisms bearing unique features in cell division. A single mitochondrion in each trypanosome cell requires a coordinated mitochondrial and nuclear division for successful cell growth. Theoretically, either the mitochondrion or the nucleus alone could signal the cell to divide. In our studies, we found that the insect form of T. brucei divides under the control of mitochondrion whereas the bloodstream form is regulated by its nucleus. This ready change of command on cell division in the same organism has never been observed previously, because cell division is always tightly controlled by mitosis in other organisms. We have since examined in T. brucei the Polo-like kinase (TbPLK) and Aurora-like kinase (TbAUK1), known to play pivotal roles in controlling both mitosis and cell division in other organisms, to find out how they function in T. brucei. TbPLK turns out playing no role at all in mitosis. It controls only cell division and localizes outside the nucleus. TbAUK1 resides in a novel protein complex and trans-localizes at the completion of mitosis from the nuclear spindle to the dorsal side of the cell and transcends down from the anterior to the posterior end of the cell to divide it into two. This is a novel pattern of cell division. We plan to look into the detailed mechanism behind it, delineate the functions of TbPLK and TbAUK1 in conducting this unique event and develop it into a potential target for anti-sleeping sickness chemotherapy.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI021786-26
Application #
8197149
Study Section
Pathogenic Eukaryotes Study Section (PTHE)
Program Officer
Mcgugan, Glen C
Project Start
1984-12-01
Project End
2013-11-30
Budget Start
2011-12-01
Budget End
2013-11-30
Support Year
26
Fiscal Year
2012
Total Cost
$382,388
Indirect Cost
$134,888
Name
University of California San Francisco
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Bessat, Mohamed; Knudsen, Giselle; Burlingame, Alma L et al. (2013) A minimal anaphase promoting complex/cyclosome (APC/C) in Trypanosoma brucei. PLoS One 8:e59258
Sun, Lu; Wang, Ching C (2011) The structural basis of localizing polo-like kinase to the flagellum attachment zone in Trypanosoma brucei. PLoS One 6:e27303
Li, Zhi; Umeyama, Takashi; Li, Ziyin et al. (2010) Polo-like kinase guides cytokinesis in Trypanosoma brucei through an indirect means. Eukaryot Cell 9:705-16
Gourguechon, Stephane; Wang, Ching C (2009) CRK9 contributes to regulation of mitosis and cytokinesis in the procyclic form of Trypanosoma brucei. BMC Cell Biol 10:68
Li, Ziyin; Umeyama, Takashi; Wang, C C (2009) The Aurora Kinase in Trypanosoma brucei plays distinctive roles in metaphase-anaphase transition and cytokinetic initiation. PLoS Pathog 5:e1000575
Li, Ziyin; Lee, Ju Huck; Chu, Feixia et al. (2008) Identification of a novel chromosomal passenger complex and its unique localization during cytokinesis in Trypanosoma brucei. PLoS One 3:e2354
Li, Ziyin; Umeyama, Takashi; Wang, Ching C (2008) The chromosomal passenger complex and a mitotic kinesin interact with the Tousled-like kinase in trypanosomes to regulate mitosis and cytokinesis. PLoS One 3:e3814
Li, Ziyin; Lindsay, Megan E; Motyka, Shawn A et al. (2008) Identification of a bacterial-like HslVU protease in the mitochondria of Trypanosoma brucei and its role in mitochondrial DNA replication. PLoS Pathog 4:e1000048
Li, Ziyin; Wang, Ching C (2008) KMP-11, a basal body and flagellar protein, is required for cell division in Trypanosoma brucei. Eukaryot Cell 7:1941-50
Gourguechon, Stephane; Savich, Jason M; Wang, Ching C (2007) The multiple roles of cyclin E1 in controlling cell cycle progression and cellular morphology of Trypanosoma brucei. J Mol Biol 368:939-50

Showing the most recent 10 out of 38 publications