Expression of RGS16 and RGS18 during MK differentiation. Cord-blood CD34⁺ cells were cultured in MK medium with TPO and SCF. (A) Flow cytometry analysis of MK culture. Different fractions were sorted using the CD34, CD41, and CD42 markers. Cells were acquired in a morphologic gate which excluded dying cells. CD34⁺CD41^–CD42^– subsets were sorted after staining cells with an anti-CD34–FITC antibody. Numbers in the quadrants represent the percentage of each population in the culture. (B) Level of mRNA expression in these fractions. □ indicates the immature CD34⁺-cell fraction (CD34⁺, CD41^–, CD42^–); ▦, the immature MKs (CD41⁺, CD42^low); ▪, the mature fraction (CD41⁺, CD42⁺). *P < .01. Data are mean ± SD of 3 independent experiments performed in triplicate. (C) Level of RGS16 and RGS18 mRNA expression in platelets. mRNA was extracted from these cells, and quantitative RT-PCR with specific primers for RGS was performed as described in “Materials and methods.” β2-Microglobulin amplification was used to confirm that the samples contained similar amounts of cDNAs. Data represent the mean ± SD of 3 independent experiments.