BMSSCs express high levels of SDF-1. (A) MACS-isolated preparations of STRO-1⁺ BMMNCs were partitioned into different STRO-1 subsets according to the regions, STRO-1^bright and STRO-1^dull using FACS. Total RNA was prepared from each STRO-1 subpopulation and used to construct a STRO-1^bright subtraction hybridization library as described in “Materials and methods.” (B-C) Replicate nitrocellulose filters, which have been blotted with representative PCR products amplified from bacterial clones transformed with STRO-1^bright subtracted cDNA. The filters were then probed with either [³²P] deoxycytidine triphosphate (dCTP)–labeled STRO-1^bright (B) or STRO-1^dull (C) subtracted cDNA. The arrows indicate differential expression of 1 clone containing a cDNA fragment corresponding to human SDF-1. (D) Reverse transcriptase (RT)–PCR analysis demonstrating the relative expression of SDF-1 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) transcripts in total RNA prepared from freshly MACS/FACS-isolated BMMNC STRO-1 populations prior to culture. bp indicates base pair.