Proper brain function requires the establishment and maintenance of effective neural circuits. Neural circuit development entails axon guidance, synaptic target selection, synapse formation, and synaptic growth and remodeling in response to developmental and environmental cues. Large protein complexes in both the pre- and post-synaptic cells act to coordinate synapse maturation, which involves clustering and aligning of the pre-synaptic neurotransmitter-releasing machinery with neurotransmitter receptors and signaling proteins. Evidence suggests that once formed, synapses are maintained over the lifetime of an organism. While mechanisms of axon guidance and synapse development have been well studied, little is known about the mechanisms involved in axon and synapse maintenance. Our lab is using genetic screens in Drosophila to uncover the molecular mechanisms that form and maintain synapse integrity. One of the most interesting mutations we've uncovered in the type of screen mentioned above is in With No Lysine [K] (wnk), a conserved serine-threonine kinase that has been implicated in a number of human diseases including hypertension, hereditary neuropathy and cancer. Although Wnk is highly expressed in the nervous system, its function there has not been described. We found that wnk mutant flies have defects in axon transport of synaptotagmin, a protein involved in calcium-dependent vesicle release. Interestingly, Wnk mutants also show significant synaptic retraction, indicating that mechanisms of synapse stability are compromised. In addition, we uncovered a novel interaction between Wnk and the Rab3-GEF, an activator of the Rab3 GTPase involved in vesicle and protein trafficking at the synapse.
We aim to define the mechanism by which WNK controls axon and synapse maintenance using Drosophila as a model. We will identify the domains that are critical for WNK function at the synapse and determine the sub-cellular localization of WNK. We will also define the novel interaction between WNK and Rab3-GEF that we've discovered and identify proteins in the WNK signaling pathway. In addition, we aim to extend our findings to mammalian sensory neurons by using mouse dorsal root ganglion (DRG) cultures to study axon integrity and synapse formation in the absence of WNK. Results from these studies will lead to novel insights into how WNK shapes the development and maintenance of the synapse. In addition, because the mammalian orthologs of WNK have been implicated in hereditary sensory and autonomic neuropathy type II (HSANII), study of the WNK signaling pathway may also yield novel insights into this and other neuropathic disease, including identification of therapeutic candidates.
Axon and synapse development are crucial for establishing and maintaining neuronal circuits and brain function throughout life. Defining the molecular mechanisms that control these processes is therefore critical to our understanding or normal brain function as well as how dysfunction occurs. We plan to characterize the role of the serine/threonine kinase Wnk and delineate its role in regulating axon and synapse development and maintenance. The results of these experiments will not only provide novel and fundamental insights into mechanisms regulating the control of synaptic maintenance, but also lead to possible therapeutic targets for human diseases, including neuropathies such as hereditary sensory and autonomic neuropathy type II (HSANII).
