RT-PCR analysis of CXCR4 mRNA expression in candidate HSC. CD34⁺, c-kit⁺, Rh123^dull(lanes 1 and 2) and CD34⁺, c-kit⁺, Rh123^bright (lanes 3 and 4) cells were FACS-sorted as described and subjected to RT-PCR analysis for CXCR4 mRNA. Negative control reaction (no template) is shown in lane 5. Specificity of the PCR products shown was confirmed by Southern blotting (data not shown) .