Crx, an Otx-like homeobox gene, is expressed primarily in the photoreceptors of the retina and in the pinealocytes of the pineal gland. The CRX homeodomain protein is a transactivator of many photoreceptor/pineal-specific genes in vivo, such as rhodopsin and the cone opsins. Mutations inCrx are associated with the retinal diseases, cone–rod dystrophy-2, retinitis pigmentosa, and Leber's congenital amaurosis, which lead to loss of vision. We have generated transgenic mice, using 5′- and/or 3′-flanking sequences from the mouse Crxhomeobox gene fused to the β-galactosidase (lacZ) reporter gene, and we have investigated the promoter function of the cell-specific and developmentally regulated expression ofCrx. All of the independent transgenic lines commonly showed lacZ expression in the photoreceptor cells of the retina and in the pinealocytes of the pineal gland. We characterized the transgenic lines in detail for cell-specific lacZexpression patterns by 5-bromo-4-chloro-3-indolyl β-d-galactoside staining and lacZimmunostaining. The lacZ expression was observed in developing and developed photoreceptor cells. This observation was confirmed by coimmunostaining of dissociated retinal cells with thelacZ and opsin antibodies. The ontogeny analysis indicated that the lacZ expression completely agrees with a temporal expression pattern of Crx during retinal development. This study demonstrates that the mouse Crx5′-upstream genomic sequence is capable of directing a cell-specific and developmentally regulated expression of Crx in photoreceptor cells.