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The development of novel methods for the targeting and manipulation of neural circuits in vivo 10.17863/CAM.48580 Lee, Hassal 000000034782128X Tripodi, Marco 0000000268276690 Neural networks are at the core of the brain’s ability to compute complex responses to our external environment. Clinically, network dysfunction is emerging as a key component of several psychiatric and neurodegenerative disorders such as Alzheimer’s disease or schizophrenia. However, our ability to precisely and safely manipulate neural networks for research and deliver network-specific therapy remains limited. To address this problem, our lab recently developed a monosynaptically restricted Self-Inactivating Rabies virus (SiR) which enables the targeting of neural circuits without cytotoxicity. To expand the scope of SiR we further developed the technology in two directions: A) By incorporating the CRISPR/CAS9 gene-editing machinery into the SiR genome to successfully edit endogenous loci in vitro and in vivo. B) By designing an improved second generation SiR virus (SiR 2.0) which applies the same SiR technology to a challenge rabies strain (CVS-N2C). SiR 2.0 demonstrates increased neurotropism, increased trans-synaptic transfer efficiency and markedly decreased immunogenicity compared to the SiR 1.0 vector. These advancements expand the scope of SiR viruses to be used in the genome-editing of circuits in vivo. A combined SiR 2.0 CAS9 virus, in physiology, allows us to investigate the roles of genes within circuits in the brain function of live animals. For therapy, it paves the way for the rabies virus’ potential use to edit disease-related genes in dysfunctional circuits. Despite the circuit-basis of many neurological disorders, existing gene therapy vectors are not circuit specific. In addition, the practical difficulties of delivering therapeutic agents at high doses into the central nervous system exacerbates our inability to achieve high therapeutic loads into affected circuits. In contrast, a SiR 2.0 CAS9 virus would, following injection into peripheral organs, trans-synaptically spread into desired circuits of the central nervous system that are affected in neurological disease (e.g. networks demonstrating pathological protein propagation in neurodegenerative disorders) and edit disease-related genes. Lastly, our interest in network-level pathological protein propagation also led us to investigate the biology behind this observation. Due to additional evidence that a significant number of other proteins in physiology also show interneuronal movement, we hypothesised that perhaps this is an overlooked phenomena in neurobiology which could have key implications University of Cambridge 2020-05-16 Thesis Doctoral Doctor of Philosophy (PhD) en https://www.repository.cam.ac.uk/handle/1810/301511 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/8fea37b9-05f9-4316-b4b1-42111918384f/download 87eda9de84448d1f82354d60eee3eb5f https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/1bfe2449-410a-4257-b4ba-b2071618c776/download cf645732545aa1bb666f0f7b4752718f https://www.rioxx.net/licenses/all-rights-reserved/ circuit-tracing CRISPR-CAS9 Rabies Virus neurodegeneration gene therapy viral gene therapy interneuronal protein transfer