Cre Recombinase: You Can't Live with It, and You Can't Live Without It.

The development of conditional gene targeting has greatly advanced our knowledge of human retinal diseases, but issues have arisen related to the use of some Cre-expressing mouse lines. In this article, we discuss potential problems associated with transgenic Cre expression-induced degeneration and alteration of rod photoreceptors and retinal pigment epithelium (RPE). Our strategy for circumventing RPE degeneration by induced transient Cre expression uses a single intravitreal doxycycline injection in a tetracycline-inducible RPE-specific Cre mouse line, which results in productive Cre-mediated recombination efficiently in the RPE. As constitutive expression of Cre in the RPE alters RPE biology, this inducible Cre/lox system provides an opportunity for conditional gene targeting in the RPE, a tissue that is closely related to photoreceptor degeneration, age-related macular degeneration, and diabetic retinopathy.