Throughout the nervous system there is evidence that the refinement and modulation of neural circuitry is driven not only by synapse formation, but also by the regulated disassembly of previously functional synaptic connections. Very little is known about the molecular mechanisms that regulate and achieve synapse disassembly in the nervous system of any organism. We have developed high-throughput assays for synapse disassembly that, combined with a newly synthesized genome-scale dsRNA collection, will allow us to screen the genome for the molecules that are involved in synapse disassembly. Using this strategy we hope to define the core cellular program that controls synapse stability versus disassembly. To date we have identified three genes that cause a dramatic increase in synapse disassembly when these genes are mutated or knocked-down using dsRNA. Our work on one of these genes has been published. The two other genes implicate the TGFb signaling pathway and the spectrin-based cytoskeleton in the mechanisms of synapse stabilization and disassembly. A second major focus of this grant will be the analysis of these two newly isolated genes. Finally, a third major focus of this grant is to place these three genes into a broader signaling context in order to gain insight into how synapse disassembly is regulated during normal development and, possibly, during neuro-degenerative disease. Importantly, one of the signaling pathways that we are studying has been implicated in diverse neurological disease states. We have documented synapse disassembly in a mutation that disrupts the multi-protein dynactin complex and the retrograde motor dynein. These molecules have been implicated in the etiology of amyotrophic lateral sclerosis (ALS) in mice and human. ALS is a debilitating progressive neurodegenerative motoneuron disease. Dynactin has also been demonstrated to bind Lis1, the protein product of the disrupted gene causing type 1 Lysencephaly. A more detailed understanding of the subcellular functions of dynein and dynactin may broaden our understanding of these debilitating diseases. More generally, our identification of other interacting signaling pathways that specify how dynamic synaptic connections are regulated and stabilized mat impact our understanding of a broad range of neurological disorders ranging from developmental diseases, to learning deficits and neurodegenerative disease.
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