Syn-NES-jRCaMP1b AAV (Serotype 8)

Viral vectors have become a widely used tool in biological sciences, including neurobiology, because they can control the expression of target genes in various tissues in both temporal and spatial ways. In recent years, many studies have utilized recombinant viral vectors derived from adeno-associated virus (AAV) as gene delivery tools. AAV is a single-stranded DNA virus with a small (~20nm) protein capsule that belongs to the family Parvoviridae. AAV is often referred to as a dependency virus due to its inability to replicate without a helper virus co-infection (usually adenovirus or herpes virus infection). AAV infection produces only a mild immune response and is considered non-pathogenic, a fact also reflected in the lower biosafety requirements of recombinant AAV (rAAV) compared to other popular viral vector systems. Within the transduced cells, the rAAV vector genome exists as free concatemers, limiting the risk of insertional mutagenesis. Due to its low immunogenicity and lack of cytotoxicity, AAV-based expression systems offer the possibility of expressing target genes for months in quiescent cells.

The production system of rAAV vectors usually consists of a DNA vector containing a transgene expression cassette flanked by inverted terminal repeats derived from AAV2. The construct size is limited to about 4.7-5.0 kb, which corresponds to the length of the wild-type AAV genome. rAAV is produced in a cell line. The expression vector is co-transfected with a helper plasmid that mediates the expression of the AAV rep gene, which is important for viral replication, and the cap gene, which encodes proteins that form the capsule. In addition, specific adenoviral genes required for replication are expressed in trans. In recent years, a large number of naturally occurring AAV serotypes have been described, which differ mainly in the surface properties of the capsid. Currently, packaging systems for about 10 different serotypes are available for the construction of vectors.