Passage Trypanosoma Brucei Is a Eukaryotic Parasite That Causes Sleeping Sickness

Passage
Trypanosoma brucei is a eukaryotic parasite that causes sleeping sickness in Sub-Saharan Africa.  The cell cycle of T. brucei differs from that of higher eukaryotes.  For example, the chromatin does not condense during mitosis, and the nuclear envelope remains intact.  In addition, the nucleus divides before cell division, and the cell divides along the longitudinal axis (Figure 1) .
Figure 1  Mitosis in T. bruceiA culture of T. brucei was arrested in S phase of the cell cycle by overnight incubation with the reversible inhibitor hydroxyurea.  The cells were then washed, and their progression through the cell cycle was monitored by flow cytometry and microscopy.  A subset of the culture was first exposed to the drug VX-680, which arrests cells upon completion of metaphase.  The results are shown in Figure 2.
Figure 2  Percentages of a population of T. brucei cells in each phase of the cell cycle, measured at different time points in the (A) absence and (B) presence of VX-680
Adapted from Li Z, Umeyama T, Wang CC. The Aurora Kinase in Trypanosoma brucei plays distinctive roles in metaphase-anaphase transition and cytokinetic initiation. PLoS Pathog. 2009;5(9) :e1000575.
-Why were T. brucei cells incubated with hydroxyurea overnight and washed afterward?

A) To ensure that most cells were in the same phase of the cell cycle at each time point measured
B) To determine how inhibition of DNA synthesis affects the progression of the cell cycle
C) To limit the size of the T. brucei cells prior to their entrance into mitosis
D) To promote synthesis of the proteins needed for entry into mitosis

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