Gene expression in ALDHHi, ALDHLow, side population, and non-side population cells isolated from CWR-R1 cells. ABCG2, ALDH1A1, ALDH4A1, ALDH7A1 and ALDH9A1 gene expression was detected by real-time PCR in CWR-R1 cells isolated by the side population and ALDEFLUOR™ assays. Gene expression was normalized to GAPDH and fold change in gene expression in each population was calculated based on the formula: 2-(ΔΔdCt). ABCG2 expression was the highest in the side population with 5.4-fold increase compared to non-side population (A), whereas ALDH1A1 expression was highest in NSP (A) and ALDHHi cells (B). Approximately 26-fold and 30-fold increase in ALDH1A1 gene expression was observed in NSP (A) and ALDHHi cells (B) respectively as compared to their counter populations. Expression of ALDH4A1, ALDH7A1 and ALDH9A1 genes was not significantly different in any of the populations (A and B). NSP, Non-Side Population; SP, Side Population.