Crx is a transcription factor which is predominantly expressed in developing and mature photoreceptor cells in the retina, and plays a crucial role in the terminal differentiation of both rods and cones Crx is one of the earliest-expressed genes specifically in photoreceptor precursors, allowing us to trace photoreceptor precursor cells from embryonic stages to adult stage by visualizing Crx-expressing cells In the Current study, we generated a transgenic mouse line which expresses enhanced green fluorescence protein (EGFP) in the retina driven by the Crx promoter using bacterial artificial chromosome (BAC) transgenesis EGFP-positive cells were observed in the presumptive photoreceptor layer in the retina at embryonic day 15 5 (E15 5). and continued to be expressed in developing and mature photoreceptor cells up to adult stage We sorted EGFP-positive photoreceptor precursors at E17.5 using fluorescence-activated cell sorter (FACS). and subsequently performed microarray analysis of the FACS-sorted cells We observed Various photoreceptor genes. especially cone genes, are enriched in the EGFP-positive cells, indicating that embryonic cone photoreceptor precursors are enriched In addition, we found that most of the EGFP-positive cells were post-mitotic cells Thus, the transgenic line we established can serve as a useful tool to Study both developing and mature photoreceptor cells, including embryonic cone precursors whose analysis has been difficult (C) 2010 Elsevier Inc All rights reserved