Experimental Animal Division

Cone-rod homeobox containing gene (CRX) is a transcription factor that is predominantly expressed in developing and mature photoreceptor cells in the retina, and plays a crucial role in the terminal differentiation of rods and cones. Crx is one of the earliest expressed genes in photoreceptor precursor cells [1-4]. To obtain the regulation of Cre expression in photoreceptor precursor cells, Furukawa and colleagues established a transgenic mouse line (Crx-CreERT2) that expresses CreERT2 under the control of a 2-kb promoter fragment from the Crx gene [5, 6]. Application of tamoxifen to Crx-CreERT2; CAG-CAT-Z indicator mice induced Cre-mediated recombination of a LacZ reporter transgene in the developing photoreceptor layer. They also inactivated the retina and anterior neural fold homeobox (Rax) gene in early postmitotic photoreceptor precursor cells using the CreERT2 system and revealed that the expression of the transcription factor orthodenticle homolog 2 (Drosophila) (Otx2) was severely attenuated in the Rax-induced conditional knockout retina [6]. Crx-CreERT2 transgenic mice allow us to regulate gene expression in photoreceptor precursor cells from the embryonic to the adult stage.