| Neurons are unique cells with complex and diverse morphologies reflective of their function as the information processors of the nervous system. How do neurons transform from morphologically simple cells to neurons bearing elaborate axons and dendrites? The process of sculpting and maintaining the morphology of a neuron shares the common requirement of regulating the neurons' cytoskeleton. One of the main regulators of cytoskeleton, particularly the actin cytoskeleton, is the Rho family of small GTPases.; My thesis centers around understanding how the regulation of the Rho GTPases shapes the neuron. I have approached this question by two distinct methods. First, through direct manipulation of the Rho GTPases' activity, I examined the role of two RhoGTPases, Rac1 and RhoA, in neurons with established dendritic trees. By introducing dominant negative and active forms of Rac1 and RhoA, I found that they have differential functions to regulate the stability of the dendritic arbor and the formation of the post-synaptic specialization, the dendritic spine.; Second, through the use of Drosophila genetics, I examined the neuronal function of the positive and negative regulators of the Rho GTPases, the RhoGEFs and RhoGAPs. To identify RhoGEFs essential for neuronal morphogenesis, I conducted two transgenic RNAi screens. The first screen identified three RhoGEFs whose knockdown lead to disruption of normal axon projections. The second screen identified two RhoGEFs whose activity oppose the axon stabilizing activity of p190 RhoGAP. The identification of these five RhoGEFs allows for future comprehensive examination of how they function in the context of neuronal development and their opposition to p190 RhoGAP activity.; Finally, I conducted an in depth analysis of Tumbleweed, a RhoGAP similarly identified in a RNAi screen for RhoGAPs involved in neuronal morphogenesis. Through this work, I found that the RhoGAP activity of Tumbleweed is necessary for its ability to limit axon outgrowth, but is not necessary for its function in cytokinesis.; Taken together, these results demonstrate how the differential functions of the Rho GTPases allow for the generation of complex neuronal morphologies and how genome-wide approaches offers grounds for understanding how the Rho GTPases are regulated to build a neuron. |
