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EGFP fluorescence in MCF-7 human breast carcinoma cells transfected with a bicistronic mammalian expression vector encoding retinoic acid receptor (RAR) 2 and EGFP. Sister cultures were transfected with vector encoding RAR 2 and EGFP. EGFP expression was used as a shared indicator of RAR 2 and 2 abundance, thus allowing for comparison of the growth effects of matched levels of these RAR isoforms. Cells transfected with bicistronic vector encoding only EGFP served as control. For details, see the article by Farias et al. in this issue.