During normal growth and division, cells double in mass and divide into two equally-sized daughters. All cell constituents must be duplicated and then segregated equally during mitosis. For some constituents, such as the chromosomes, the underlying principles and the mechanistic details are relatively clear. For membrane-bound organelles, such as the Golgi, the principles and mechanism have been controversial. The primary aim of our research work is to understand how the cell creates another copy of the Golgi during the cell cycle and partitions them equally between the two daughter cells, thereby ensuring that this organelle is propagated through successive generations.

The Golgi lies at the heart of the secretory pathway receiving the entire output of newly-synthesized cargo proteins from the endoplasmic reticulum, modifying any bound oligosaccharides, and then sorting them to their final destinations. Typically comprising a stack of closely-apposed and flattened cisternae, the Golgi presents a complex architecture that needs to be duplicated and partitioned every cell cycle. Most studies have focused on the partitioning of the Golgi during mitosis in mammalian cells and most studies suggest that the Golgi undergoes a dramatic conversion to thousands of small vesicles that can then be stochastically distributed between daughter cells. This conversion is triggered by mitotic kinases acting on structural proteins such as GRASPs and golgins.

Golgi duplication has been more difficult to study since most mammalian cells have several hundred copies, subsumed into a ribbon-like structure next to the centrosomes and often the nucleus. This precludes facile observation of the duplication process. We have solved this problem by focusing on organisms that have only a single Golgi that undergoes duplication during the cell cycle and partitioning during mitosis. Protozoan parasites are the best model systems since many have had their genomes sequenced and a variety of molecular biological techniques are available to manipulate protein levels.

Trypanosoma brucei is the causative agent of sleeping sickness in sub-Saharan Africa, and provides a highly-simplified and organized secretory system that is ideal for studying the process of Golgi biogenesis. The duplication of the single Golgi can be observed using GFP-tagged Golgi proteins, and video fluorescence microscopy shows that the old Golgi is involved in the construction of the new. Furthermore, both are located on a novel bilobe structure that appears to act as a template, determining both the size of the Golgi and its inheritance. The composition and duplication of this bilobe are presently under investigation as is the molecular mechanism that generates the new Golgi.