Neurexin-Neuroligin Trans-synaptic Interaction: Learning-related Synaptic Growth

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DESCRIPTION (provided by applicant): Studies in a variety of memory systems have suggested that the storage of long-term memory is associated with altered gene expression, the synthesis of new proteins, and the growth of new synaptic connections. However, little is known about molecular mechanisms that initiate and maintain the structural changes associated with long-term memory. A particularly useful system for delineating these molecular mechanisms is the gill-withdrawal reflex in Aplysia. Long-term sensitization of this reflex gives rise to robust increase in growth of new synaptic connections. Recently, initial attempts have been made in identifying some molecules important for do novo synaptic formation in the developing nervous system. Specifically, synaptic cell adhesion molecules, beta-neurexin (localized at the pre-synaptic neurons) and neuroligin (localized at the postsynaptic neurons), via trans-synaptic interaction with each other, have been found to be involved in synapse formation during development. These molecules may be also involved in the synaptic growth associated with the storage of long-term memory. CASK, a pre-synaptic scaffolding protein that interacts with beta-neurexin, can translocate to the nucleus and thereby regulates gene expression. Given the requirement of altered gene expression in the storage of long-term memory, CASK as a putative retrograde signal from the synapse to the nucleus triggered by beta-neurexin-neuroligin trans-synaptic interaction is an intriguing idea. The candidate will investigate the role of neuroligin, beta-neurexin, and CASK in the synaptic growth associated with the storage of long-term memory by exploiting the experimental accessibility of the Aplysia sensory-motor neuron co-culture preparation where the pre-synaptic structural changes associated with long-term synaptic plasticity are particularly robust and easy to study. Molecular cloning, gene transfer techniques using over-expression of synaptic marker proteins, time-lapse confocal imaging of individual, fluorescently-labeled pre-synaptic sensory neuron varicosities and physiological recording of the same sensory-motor neuron co-cultures will be used for the project. The training activities will enable the candidate to acquire the skills and experience necessary to become an independent neuroscientist equipped with the latest molecular and cellular biological techniques to investigate the learning-related synaptic growth and to develop novel therapeutic approaches to the sequel of synaptic dysfunction. Results from these studies should enhance understanding of a bidirectional signaling pathway from the synapse to the nucleus that regulates synaptic growth associated with the storage of long-term memory. In addition, it may provide some clues to the causes of postnatal developmental disorders such as autism that may be caused by disruption of synaptic plasticity and perhaps suggest novel therapeutic strategies for synaptic repair and remodeling leading recovery of function after various neurological insults.