| dc.description.abstract | In order for life to continue, proper segregation of genetic materials by the process of mitosis is essential. Mitosis is facilitated by a bipolar spindle, usually composed of a symmetrical array of microtubules (MTs). MTs consist of Tubulin polymers, and are generated in vivo with the aid of nucleators. The most predominant nucleator is the γ-Tubulin Ring Complex (γ-TuRC). During mitosis, multiple pathways contribute to proper spindle formation, including centrosome-dependent, kinetochore-dependent, and a recently discovered pathway in which new MTs are nucleated from the sides of existing MTs. This last pathway relies on the Augmin complex, a template-dependent MT nucleator which recruits γ-TuRC to the spindle. Mitotic cells lacking Augmin have weak spindles due to a lower density of MTs and in human cells, Augmin reduction also causes centrosome fragmentation. To date, very little is known about the functional properties of Augmin. I have purified individual Augmin subunits and examined their properties in vitro. I show that the Augmin subunits Dgt4 and Wac are responsible for interaction with MTs and that Dgt6, Dgt3 and Dgt5 interact with the γ-TuRC subunit Dgp71WD. I have also shown that Wac protects MTs from destabilisation. Interestingly, the Augmin complex promotes MT assembly in the absence of γ-TuRC, suggesting a novel function for Augmin. I have also successfully purified intact Augmin complex. With this, I determined some of the relationships between Augmin subunits and generated a model of how Augmin might recruit γ-TuRC to MTs. Lastly, I have determined that at least one subunit, Wac, plays a role in MT organisation beyond mitosis. This work significantly improves our understanding of the Augmin complex and provides an excellent complement of tools for further investigation. | en_GB |
