Re-writing Connections in the Living Brain

Recent advances in Neuroscience are demonstrating how the introduction of a new technique (such asviral tracing or optogenetics) makes it now possible to answer fundamental questions that have long been recalcitrant to traditional approaches. Mapping the structure and function of neural circuits is an important prerequisite to understand how groups of interconnected neurons produce perceptions and drive behavior. One existing challenge is to unambiguously identify both the activity and functional significance of specific connections (synapses) within a circuit. To begin addressing this problem, we recently developed a new transgenic activity-dependent, multi-color system to label synapses based on their activity (i.e. through trans-synaptic reconstitution of fluorescent proteins, X-RASP1). This system greatly facilitated our study of thermosensory and hygrosensory circuits2,3, is now widely used in the field 2,4-16, and still represents the only approach for retrospective labelling of synapses (rather than whole neurons), based on their activity, in living animals1. We now propose to develop new methods to reengineer the connectivity of brain circuits, by adding or removing specific connections to test hypotheses on their significance. We propose to develop a new generation of tools which will combine functional intracellular domains for synaptic pruning or stabilization with our X-RASP toolkit (and other synthetic ligand-receptor strategies). These transgenic tools will allow us to developmentally re-wire connections in the intact brain to test specific hypotheses on circuit dynamics and behavior. As before, we will use the fruit fly Drosophila as a versatile platform to demonstrate their use in vivo. Our unique mix of molecular engineering and in vivo work in Drosophila has the potential to significantly accelerate the development of innovative technologies that can later be applied to any genetic model system, and to expand our mechanistic understanding of how