Investigating the role of a conserved serine/threonine kinase, SAX-1, in higher-order dendrite pruning

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PROJECT SUMMARY Neurite remodeling is a highly conserved process that refines and establishes a mature nervous system. A failure in neurite remodeling leads to neurological and neurodevelopmental disorders. While developmental dendritic pruning, a means of neurite remodeling, has been extensively studied, the cell-biological mechanisms that control pruning remain poorly understood. Specifically, there is a fundamental gap in understanding how neurons can selectively prune specific dendritic branches while leaving sister branches intact. The long-term goal is to identify and understand the cell-biological mechanisms that direct branch-specific pruning. The nematode Caenorhabditis elegans inner labial 2 (IL2) neurons, upon entering a developmental diapause, extend a stereotypical dendritic arbor that is pruned when development is resumed – leaving primary dendrites intact. The stereotypic remodeling of IL2 neurons allows experimental access to elucidate the cell-biological mechanisms that confer selective pruning. The central hypothesis is that SAX-1, an evolutionarily conversed serine/threonine kinase, functions in a molecular pathway that links calcium signaling to cytoskeletal dynamics in higher-order dendrite branches to direct selective pruning. The rationale for this proposal is that studying the role SAX-1 during IL2 remodeling will offer a framework to understand how local regulation of the cytoskeleton confers branch-specific pruning. The central hypothesis will be tested by the following specific aims: 1) determine how SAX-1 directs pruning of higher-order IL2 dendrite branches; and 2) identify the genetic pathway in which SAX- 1 acts to regulate the cytoskeleton during pruning. The research proposal is innovative because it will 1) be the first to establish C. elegans as a model system for studying pruning, 2) elucidate a novel role for SAX-1 in dendritic pruning, and 3) determine how the cytoskeleton is locally regulated during pruning. The proposed research is significant because elucidating the fundamental cell-biological mechanisms of branch-specific pruning will significantly advance our understanding of developmental neurite remodeling. This understanding is a critical to inform us about how neurodevelopmental processes go awry in disorders such as Down Syndrome.