AAV9 and Cre: a one-two punch for a quick cardiac knockout

This editorial refers to ‘Rapid and highly efcient inducible cardiac gene knockout in adult mice using AAV-mediated expression of Cre recombinase’ by S. Werfel et al. , pp. 15–23, this issue. Knockout mice have revolutionized our ability to conduct biomedical research and no area has benefited more than cardiovascular disease. The knockout (or genetic deletion) of (a) specific gene(s) has provided a clearer understanding of the roles a gene plays in development, normal physiology, and in responses to injury, vasomotor regulation, and excitation/contraction coupling to name a few. These advances notwithstanding, the utility of traditional knockout mice can be limited in cases where the gene deletion causes embryonic lethality, or when a tissue-specific knockout is desired to avoid having off-target effects limit the study. The application of Cre-lox technology to transgenesis has provided a powerful tool in helping investigators create tissue-specific knockouts.1 The Cre-lox strategy requires the breeding of two separate lines of genetically manipulated mice: ‘floxed’ mice in which the gene of interest has been flanked by two loxP sites using ‘knock-in’ techniques, and another line of transgenic mice in which a tissue-specific promoter is used to drive the expression of Cre-recombinase. By crossing these two strains, mice are obtained in which tissue-specific expression of Cre results in deletion of the gene of interest due to the action of the Cre-recombinase enzyme that excises the genomic region flanked by the loxP sites. …