Adeno-associated viruses (AAVs) are small viruses belong to the genus Dependoparvovirus.With a length of 4.7 kb, the AAV genome is composed of two open reading frames (ORFs), Cap and Rep, which are flanked by inverted terminal repeats (ITRs). Till now, 11 natural serotypes of AAVs have been identified. AAVs are nonenveloped viruses, the gene expression and replication can be activated when the helper viruses are present. Compared to other vectors, the frequency of random integration into the genome of the host cell is much lower. In addition, removing Rep and Cap can further prevent the integrative capacity.
Due to the lack of replication ability and extremely low immunogenicity, AAV has been widely used in neuroscience and gene therapy. To date, there are more than 110 AAV-related gene therapies for clinical trials in the world. The disease indications include but are not limited to:
Spinal muscular atrophy
Amyotrophic lateral sclerosis
Temporal lobe epilepsy
Charcot-Marie-Tooth disease type 1A
Applications of AAV in Neuroscience
In general, we use the brain stereotactic injection technique to deliver viral vectors to specific brain regions for the expression of specific genes and fluorescence. However, it is not suitable for extensive labeling and gene expression in multiple brain regions because of the limited virus infection efficiency. In this case, the injection of AAV can solve this problem and further improve a variety of research and gene therapy methods.
It is well-known that traditional AAV vectors cannot cross the synapses. In this case, anterograde tracing and retrograde tracing are essential to characterize neuronal networks. Among them, anterograde tracing focuses on labeling known downstream brain regions, while retrograde tracing focuses on upstream brain regions. Compared with fluorescent dyes, viral vectors have the capabilities of retrograde tracking and gene carry. The established rAAV2-retro serotype vector can be absorbed in the axon and retrograde to the nucleus for the expression of fluorescent protein along the cytoskeleton.
Fig.2 Transcriptional targeting of neuronal populations. (Haggerty, 2020)
Features of AAV
High gene delivery ability
Capsid protein diversity
High infection efficiency
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Wang, Y.; et al. Viral vectors as a novel tool for clinical and neuropsychiatric research applications. General psychiatry. 2018, 31(2).
Haggerty, D.; et al. Adeno-associated viral vectors in neuroscience research. Molecular Therapy-Methods & Clinical Development. 2020, 17: 69-82.