Spatiotemporal control of genome engineering in cone photoreceptors

Background Cones are essential for color recognition, high resolution, and central vision; therefore cone death causes blindness. Understanding the pathophysiology of each cell type in the retina is key to developing therapies for retinal diseases. However, studying the biology of cone cells in the rod-dominant mammalian retina is particularly challenging. In this study, we used a bacterial artificial chromosome (BAC) recombineering method to knock in the “CreER T2 ” sequence into the Gnat2 and Arr3 genes, respectively and generated three novel inducible CreER T2 mice with different cone cell specificities. Results These models ( Gnat2 CreERT2 , Arr3 T2ACreERT2 , and Arr3 P2ACreERT2 ) express temporally controllable Cre recombinase that achieves conditional alleles in cone photoreceptors. Cre-LoxP recombination can be induced as early as postnatal day (PD) two upon tamoxifen injection at varying efficiencies, ranging from 10 to 15% in Gnat2 CreERT2 , 40% in Arr3 T2ACreERT2 , and 100% in Arr3 P2ACreERT2 . Notably, knocking in the P2A-CreERT2 cassette does not affect cone cell morphology and functionality. Most cone-phototransduction enzymes, including Opsins, CNGA3, etc. are not altered except for a reduction in the Arr3 transcript. Conclusions The Arr3 P2ACreERT2 mouse, an inducible cone-specific Cre driver, is a valuable line in studying cone cell biology, function, as well as its relationship with rod and other retinal cells. Moreover, the Cre activity can be induced by delivering tamoxifen intragastrically as early as PD2, which will be useful for studying retinal development or in rapid degenerative mouse models.