A central goal in neuroscience is to understand behavior in terms of the activity and connectivity of specific neurons. Anatomical tracings have revealed the mesoscale connections in the brain, but this dataset lacks functional utility without the ability to behaviorally study neurons with specific connections to other brain regions. Recently, a number of technological advances have enabled these types of experiments, including re-engineered viruses to target specific neuron types and deliver genes of interests. This methodology is important because genetic targeting of specific neurons allows one to draw a link between a neurons's anatomy (the regions it projects to) and its function (the information it encodes). This project will explore the engineering of novel tools that will significantly improve existing retrograde tracing techniques and thereby enable mapping behavioral functions to specific neuron types. The resulting tools will be made broadly available to the community to increase their impact and utility.
As systems neuroscience is adopting tools from molecular biology there is an increasing appreciation for the importance of circuit-specific technologies, for instance targeting neuron-types defined by their projections using retrograde viral strategies for anatomical and genetic labeling. These tools have been critical for cell-type specific recordings using genetic activity indicators, or control using optogenetic actuators. Nevertheless, the efficiency and variable tropism (i.e. inability to target all cell types) of existing retrograde viruses presents a challenge for these experimental approaches. To overcome this challenge, two methods are proposed to generate reagents that will provide a non-toxic profile while maximizing efficient labeling of the targeted population. The methods will exploit well-understood molecular mechanisms for viral internalization to overcome tropisms, as well as classic tracers improved using a novel protein ligation technique. These reagents will be suitable for precise and robust anatomical tracing, for induction of opto- and chemicogenetic actuators. Therefore we expect that these improved reagents will allow for more efficient and less variable projection-based targeting of neurons with molecular cargo and facilitate new types of circuit-based mapping experiments.
