Total RNA was extracted from 8500 cells sorted from each bone marrow or liver population (Absolutely RNA Nanoprep Kit; Stratagene, La Jolla, CA). DNase treatment of all RNA extracts was included according to the manufacturer's instructions. cDNA was prepared by reverse transcription under standard conditions using random hexamer priming (First-Strand cDNA Synthesis Kit; Amersham Biosciences). PCR amplification of c-kit and glyceraldehyde phosphate dehydrogenase (GAPDH) cDNA was performed using FastStart Taq DNA Polymerase (Roche) and the following primer pairs: c-kit forward, 5′-GCACTTGAGTGCTACACTCTTGCACCT-3′; c-kit reverse, 5′-TCTTCAGAACTGTCAACAGTTGGACAACA-3′; GAPDH forward, 5′-TTCCAGTATGACTCCACTCACG-3′; and GAPDH reverse, 5′-GTTCACACCCATCACAAACATG-3′. Conventional PCR conditions using one primer pair per reaction tube were as follows: 95°C for 1 minute, 55°C for 1 minute, and 72°C for 1 minute, 40 cycles. Multiplex PCR to amplify both genes in the same reaction tube was performed under identical conditions with both primer pairs added to the same PCR reaction tube.