Skip to main content
. 2011 Feb 14;22(6):669–677. doi: 10.1089/hum.2010.204

FIG. 2.

FIG. 2.

Strategies for cell type–selective transgene expression with recombinant adeno-associated virus (rAAV). (A) Promoter specificity. Schematic showing cell-type specificity of short promoter fragments in rAAV. The cytomegalovirus (CMV) promoter drives expression nonselectively in neurons and glia, while the neuron-specific enolase (NSE) promoter is selective for neurons, and the melanin-concentrating hormone (MCH) promoter targets expression to a subpopulation of neurons in the lateral hypothalamus. (B) Tropism specificity. AAV capsid proteins lead to differential infectivity between cell populations based on recognition between capsids and cell surface receptors. (C) Cre-dependent intersectional genetic switches. (i) Insertion of a 1–2 kb stop cassette after the promoter (P) and upstream of a gene of interest (GOI). The stop cassette is flanked by two loxP sites which are the recognition sequences that recombine in the presence of Cre. After recombination, the stop cassette is excised (one loxP site remains) and transcription of the GOI proceeds. (ii) Use of a flip-excision (FLEX) switch to activate gene expression specifically in the presence of Cre-recombinase. The GOI is inverted between two pairs of heterotypic, antiparallel lox-type recombination sites, which first undergo an inversion of the coding sequence, followed by excision of two sites, leading to one of each orthogonal recombination site oppositely oriented and incapable of further recombination. (iii) Demonstration of Cre-dependent transgene expression using a FLEX switch. The top panels show tissue from a wild-type mouse brain co-injected with both a rAAV2/1-ChR2-EGFP virus and a rAAV2/1-FLEX-rev-ChR2-mCherry virus. Expression of EGFP is broadly observed while mCherry is not expressed in the absence of Cre. Injection of rAAV2/1-FLEX-rev-ChR2-mCherry into an Agrp::Cre mouse (bottom panel) shows expression of the mCherry signal only in the arcuate nucleus, which is the sole location of AGRP neurons in the brain. Adapted from Journal of Neuroscience (Atasoy et al., 2008), copyright 2008.