Investigating Synaptic Growth Through Live Imaging and Genetics.

University Of California-San Francisco, San Francisco CA

Investigators

Abstract

Dr. Davis will combine live imaging techniques with Drosophila genetics to visualize synapse remodeling in vivo and analyze the underlying molecular mechanisms that control synapse remodeling in real time. Synaptic connections are the sites of communication between neurons. The precise modification of synapses is essential to the correct wiring of neuronal circuitry during development and to the modification of neural circuits during adult plasticity. Despite the identification of myriad synaptic proteins, the mechanisms that control synaptic bouton formation, stabilization and retraction are still poorly understood. Dr. Davis will characterize, with fine temporal resolution, the sequence of events by which new synapses are assembled, stabilized and disassembled. Combined with a genetic analysis, these studies aim to identify important molecular mechanisms underlying the events of synapse remodeling. In previously published studies, Dr. Davis has demonstrated that mutations in the cell adhesion molecule Fasciclin II and the microtubule associated protein Futsch impair synaptic growth. Dr. Davis will now examine how these and other molecules affect synapse growth in real time. Preliminary data from Dr. Davis demonstrate that new presynaptic varicosities can be added to the nerve terminal as rapidly as 2 to 5 minutes and can be eliminated during normal development. These data challenge previous hypotheses regarding synaptic growth at this synapse, the Drosophila NMJ, that suggest that synaptic boutons are added slowly over the course of hours and, once added, are not eliminated. Dr. Davis now hypothesizes that presynaptic varicosities can form very rapidly, but only a subset of the newly formed varicosities become stabilized to form functional boutons. Dr. Davis further hypothesizes that, once stabilized, synaptic boutons are rarely eliminated. Thus, an essential growth regulatory event may be the determination of whether a new presynaptic varicosity is stabilized. The live imaging experiments proposed in this study will address this possibility in detail. Dr. Davis will also investigate the molecular mechanisms that determine whether newly formed synaptic boutons are stabilized or retracted. Preliminary data implicate the dynactin protein complex as an important regulator of synapse stabilization. Inhibition the dynactin complex causes the elimination of synaptic terminals at the NMJ. Live imaging combined with genetic analysis will precisely define how synapse elimination occurs in the dynactin mutations. Finally, Dr. Davis will use well characterized mutations that alter nerve and muscle activity to determine the roles of pre- and postsynaptic activity in the process of synaptic growth and elimination using live, in vivo imaging.