Elucidating the roles of aurora B kinase in neurons

To reveal molecular determinates that underlie the intrinsic molecular pathways within neurons that support regeneration after injury, a DNA microarray study was performed on axotomized neuronal clusters that were maintained in culture and free from glial and astrocytes contamination. The microarray data indicated that post-injury regenerative sprouting requires two distinct pathways; a cell survival response to protect against pernicious secondary processes and a regenerative response driven by modulation of the neuronal cytoskeleton. From the transcriptomic data, cell cycle associated aurora B kinase (Aurkb), which was significantly up-regulated but never investigated in the context of neurons, was identified for further work. Immunohistochemical studies revealed that Aurkb is expressed extensively and cell-specifically in neurons of certain brain structures such as the cortex, hippocampus and amygdala. Its elevated expression in the embryonic brain cortex as compared to that of an adult implies that it may be involved in the process of brain maturation. Interestingly, the changing localization of Aurkb within developing cultured neurons and particularly its localisation outside of the nucleus at various stages of neuronal maturation further suggests that it may have direct roles neurite outgrowth. Indeed, impairing Aurkb activity in cultured neurons via different experimental approaches resulted in several key neuronal deficits. Generally, neurons with inactive Aurkb were found to have either shorter or no elaborated axons. They also possessed abnormally swollen cell bodies. Enlargement of the cell body, independent of nucleus size, was related to a substantial increase in microtubule mass within the area between the nucleus and axon hillock region. Furthermore, their expanded cell bodies are bordered by several aberrant, thin, frayed and highly disorganised neuritic processes. Next, yeast 2 hybrid identified INCENP as a binding partner of Aurkb in neurons. Subsequent phosphoproteomics studies coupled with functional analysis of protein associations have further revealed that inhibition of neuronal Aurkb affected a cluster of proteins and kinases that are major players of neuronal cytoskeleton regulation and organisation. In conclusion, this is the first comprehensive study of Aurkb in the brain and neurons. Specifically, the phosphoproteomic, pharmacological and molecular knockin and knockout studies provided considerable evidence that Aurkb has key roles in neurite cytoskeleton modulation. Taken together, the work in this thesis has clearly identified a novel and alternate cell cycle independent function of Aurkb in post-mitotic neurons.