CAG-mCherry AAV (Serotype Retrograde)

Adeno-associated virus (AAV) is a non-enveloped parvovirus that carries a single-stranded DNA genome of approximately 4.7 kb. Recombinant AAV vectors are widely used for clinical gene therapy and experimental gene delivery because they enable robust, safe, and durable gene expression in non-dividing cells. AAV vectors have several advantages over other viral vectors. Wild-type AAV is non-pathogenic, and AAV vectors are typically handled at biosafety level 1, without the need for specialized equipment such as biosafety cabinets. Unlike HSV1 and rabies virus, which rely on helper viruses, AAV does not replicate prior to axonal transport, and does not require a second helper virus to initiate monosynaptic tracing. These advantages make AAV vectors relatively easy to obtain and use for neural circuit tracing.

Not only can AAV vectors express fluorescent proteins in neurons to trace their axonal projections, but recent advances now support the use of AAV vectors for both retrograde and anterograde labeling of monosynapses, as well as specific labeling of neurons that send outputs to or receive inputs from multiple specific brain regions. Anterograde trans-synaptic transduction by common AAV serotypes is rarely detectable and retrograde transduction is typically weak, but directed evolution of AAV capsid libraries has identified novel AAV capsids that demonstrate enhanced axonal transport in the mammalian brain. AAV2-retro is a variant of the AAV2 capsid that contains a 10-amino acid insertion and two additional point mutations in the heparin-binding loop. AAV2-retro demonstrated up to 100-fold greater retrograde transduction of mouse neurons compared to other common AAV serotypes.