"Gene Delivery across the Blood-Brain-Barrier, Whole-Body Tissue Clearing, and Optogenetics to understand and influence physiology and behavior"

Our research group at Caltech develops and employs optogenetics, tissue clearing, and viral vectors to gain new insights on circuits underlying locomotion, reward, and sleep. In most recent work the group has delineated novel circuits that might be at the root of sleep disturbances common to numerous neuropsychiatric disorders (Cho et al., Neuron, 2017; Oikonomou et al, 2019 Neuron 2019).  Present-day neuroscience relies on genetically-encoded tools; in both transgenic and non-transgenic animals, current practice for vector delivery is stereotaxic brain surgery—an invasive method that can cause hemorrhages and non-uniform expression over a limited volume. To address this limitation, we have developed viral-vector selection methods to identify engineered capsids capable of reaching target cell-populations across the body and brain after noninvasive systemic delivery (Deverman et al, Nature Biotechnology, 2016). We use whole-body tissue clearing to facilitate transduction maps of systemically delivered genes (Yang et al, Cell, 2014; Treweek et al, Nature Protocols, 2016). With novel AAV capsids, we achieved brain-wide transduction in adult mice after systemic delivery and sparse stochastic Golgi-like genetic labeling that enables morphology tracing for both central and peripheral neurons (Chan et al, Nature Neuroscience, 2017). Viral vectors that can efficiently and selectively deliver transgenes to target tissues after injection into the bloodstream allow us to genetically modify a high percentage of desired cells with more homogeneous coverage, without the need for either highly invasive direct injections or time-consuming transgenesis. Since CNS disorders are notoriously challenging due to the restrictive nature of the blood brain barrier, the recombinant vectors engineered to overcome this barrier can enable potential future use of exciting advances in gene editing via the CRISPR-Cas, RNA interference and gene replacement strategies to restore diseased CNS circuits. 

To overcome poor tissue penetration by visible light, optogenetics requires surgically implanted fiberoptics. By using directed evolution and machine learning, Viviana Gradinaru in collaboration with Frances Arnold (Nobel Prize Chemistry 2018) recently evolved opsins with new characteristics, including high-fluxing opsins that allow for light source at a distance and minimum invasiveness (Bedbrook et al, Nature Methods 2019). The combination of systemic viruses and powerful opsins brings noninvasive deep brain stimulation closer to reality. Modulating brain circuits in behaving animals noninvasively will be a game changer for both basic science and therapy. These recently developed capsids capable of crossing the BBB can provide solutions to the challenge of noninvasive and circuit- or cell-type-selective delivery of sensors and actuators to the CNS in transgenic and non-transgenic animals. With synergistic developments in actuators, systemic AAVs will allow researchers to modulate defined cell types and circuits across multiple deep-brain structures in a minimally invasive manner, and test the behavioral effects of this modulation in animal models. 

Selected References


Professor Viviana Gradinaru completed her B.S. at Caltech and her Ph.D. research at Stanford University and is now a Professor of Neuroscience and Biological Engineering at Caltech. Professor Gradinaru’s research interests focus on developing tools and methods for neuroscience (optogenetic actuators and sensors; tissue clearing and imaging; gene delivery vehicles) and using them to characterize circuits underlying locomotion, reward, and sleep, with the goal to inform deep brain stimulation (DBS) and better understand the underlying mechanisms of action. 

Professor Gradinaru has received the NIH Director’s New Innovator and Pioneer Awards and a Presidential Early Career Award for Scientists and Engineers, and has been honored as a World Economic Forum Young Scientist and as one of Cell’s 40 under 40. Gradinaru is also a Sloan Fellow, Pew Scholar, Moore Inventor, Vallee Scholar, and Allen Brain Institute NGL Council Member, and received the inaugural Peter Gruss Young Investigator Award by the Max Planck Florida Institute for Neuroscience. In 2017 she was the Early-Career Scientist Winner in the Innovators in Science Award in Neuroscience (Takeda and the New York Academy of Sciences) and in 2018 she received a Gill Transformative award. 

Professor Viviana Gradinaru has also been very active in teaching and service, participating with lab members in regular technology training workshops at Caltech and for summer courses at Cold Spring Harbor Laboratory as well as running the CLOVER Center (Beckman Institute for CLARITY, Optogenetics and Vector Engineering), which provides training and access to the group's reagents and methods for the broader research community.


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