The primary means by which nerve cells communicate with each other is through the release of neurotransmitter at chemical synapses. The ability of the brain to process information depends on synaptic connections forming precisely and reliably between many different types of neurons. This proposal is directed towards developing a molecular understanding of the signaling between synaptic partners that regulate synaptogenesis. It is well established that even in simple metazoans like the worm C. elegans changes in synaptic activity induce compensatory changes in synaptic strength and structure. We propose to use a combination of genetics, cell biology, molecular biology and live imaging to identify and characterize the role of molecular components of the signaling pathways that coordinate synaptic development at nerve-nerve synapses. First, we aim to describe the order of cellular events in nascent synapse formation by visualizing the recruitment of fluorescent-tagged components to newly forming synapses. We will define the order in which mitochondria, synaptic vesicles, active zone components and adhesion molecules appear at synaptic sites. We will also define the cellular mechanisms that mediate subsequent growth of the presynaptic specializations. Second, we will define the role of novel molecular components that were identified as mutants that fail to form synapses. Using a variety of molecular, genetic and protein interaction studies we will position the genes within the current molecular models of synapse assembly. Third, we will use genetic approaches to isolate and characterize genes which disrupt signaling between mechanosensory neurons and their synaptic partners in C. elegans using a novel synaptic tag which can be easily detected in live animals under a fluorescent dissecting scope. Together these approaches will help define mechanisms that cells use to identify and communicate with one another during the process of synapse formation and synaptic maintenance. While synaptogenesis is undoubtedly less complex in C. elegans than in vertebrates, it is already clear that similar pathways operate in both systems. Thus, analysis of the molecules participating in the process in C. elegans should help define a set of general and likely conserved principles that are common to synaptogenesis mechanisms in general. PUBLIC HEALTH RELEVANCE: Synaptic connections are the primary neuronal communication structures in the brain. In Alzheimer's disease, it is now well established that changes in synaptic density (i.e. loss of synaptic connections) correlate better with cognitive impairment that the hallmark plaque and tangle lesions that are also associated with the disease. Our work is focused on understanding how synaptic connections are formed. Such basic scientific understanding of brain development and function will aid in developing therapies that intervene early in disease hence slowing or arresting synaptic loss. [unreadable] [unreadable]