Expression of R4 RGS in human HSPCs and its regulation by the SDF-1/CXCR4 axis. (A) Differential mRNA levels of R4 RGS in CB-derived CD34⁺ cells (n = 12). (B) SDF-1 affects RGS mRNA expression. CD34⁺ cells were cultured in medium alone or in the presence of SDF-1 (100 ng/mL) for the indicated time points. Expression of R4 RGS was measured by RT-qPCR (n = 5). (C) AMD3100 blocks RGS induction. CD34⁺ cells were pretreated with AMD3100 (10 µg/mL) for 1 hour before stimulation with SDF-1 and quantified for R4 RGS expression (n = 6). Reported values are RGS expression relative to GAPDH. (D) SDF-1 affects RGS protein expression. CD34⁺ cells were cultured in the absence or presence of SDF-1 (100 ng/mL) for 24 hours. Expression of R4 RGS was measured by Western blotting. RGS/GAPDH intensity ratios are indicated. Statistics: 2-tailed, paired Student t test. *P < .05; **P < .01; ***P < .001.