Optogenetic, tissue clearing, and viral vector approaches to understand and influence whole-animal physiology and behavior

[Speaker] Viviana Gradinaru:1
1:Caltech, BBE, USA

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. We showed how bidirectional manipulation of mesopontine cholinergic cell bodies exerted opposing effects on locomotor behavior and reinforcement learning and how these effects were separable via limiting photostimulation to PPN cholinergic terminals in the ventral substantia nigra pars compacta or to the ventral tegmental area, respectively (Xiao et al, Neuron, 2016). In most recent work (Cho et al., Neuron, 2017), the group has delineated novel arousal-promoting dopaminergic circuits that might be at the root of sleep disturbances common to numerous neuropsychiatric disorders. Genetically encoded tools that can be used to visualize, monitor, and modulate mammalian neurons are revolutionizing neuroscience. However, use of genetic tools in non-transgenic animals is often hindered by the lack of vectors capable of safe, efficient, and specific delivery to the desired cellular targets. To begin to address these challenges, we have developed an in vivo Cre-based selection platform (CREATE) for identifying adeno-associated viruses (AAVs) that more efficiently transduce genetically defined cell populations (Deverman et al, Nature Biotechnology, 2016). As a first test of the CREATE platform, we selected for viruses that transduced the brain after intravascular delivery and found a novel vector, AAV-PHP.B, that transduces most neuronal types and glia across the brain. We also demonstrate how whole-body tissue clearing can facilitate transduction maps of systemically delivered genes (Yang et al, Cell, 2014; Treweek et al, Nature Protocols, 2016) and how non-invasive delivery vectors can be used to achieve dense to sparse labeling to enable morphology tracing in both the central and peripheral nervous systems (Chan et al, Nature Neuroscience, 2017). 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.
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