Ultrastructural study of Golgi duplication in Trypanosoma brucei.

Golgi duplication in the protozoan parasite Trypanosoma brucei has been tracked using serial thin section three-dimensional reconstructions of transmission electron micrographs. The old Golgi maintains a constant size (approximately 0.060 microm(3)) throughout the cell cycle. A morphologically identifiable new Golgi appears at approximately 0.20 of the cell cycle (defined by the size of the nucleus and lasting about 9 h) and grows from approximately 0.018 microm(3) until it is the same size as the old Golgi (by approximately 0.55 of the cell cycle). Morphologically identifiable late Golgi appear at approximately 0.58 of the cell cycle, but their volume ( approximately 0.036 microm(3)) did not change significantly. Cryoimmunoelectron microscopy was used to identify candidates for the earliest new Golgi structures, and these comprised clusters of vesicles containing Golgi reassembly stacking protein (GRASP) near an endoplasmic reticulum exit site. These results, combined with earlier fluorescence data, suggest that the new Golgi begins functioning before cisternal stacks are formed.

Centrin4 coordinates cell and nuclear division in T. brucei.

Centrins are Ca(2+)-binding proteins that have been implicated in a number of biological processes, including organelle duplication, mRNA export, DNA repair and signal transduction. In the protozoan parasite Trypanosoma brucei we have previously described TbCentrin2, which is present on a bi-lobed structure, and involved in the duplication and segregation of the Golgi complex. Recently, another centrin, TbCentrin4, was also found at the bi-lobe and has been implicated in organelle segregation and cytokinesis. We now show that cytokinesis is not inhibited, but that a dysregulation of nuclear and cell division leads to the production of zoids - daughter siblings that contain all organelles except the nucleus. Our results, therefore, suggest that TbCentrin4 is involved in processes that coordinate karyokinesis and cytokinesis.