Real-time PCR analysis for the expression levels of ALDH1A1 and ALDH1A2 during the culture activation of HSCs. The PCR data are expressed as the percentage of HSCs-d3. **P-value, paired t-test (n = 3) (compared to HSCs-d3), ALDH1A1/HSCs-P3: 0.003, ALDH1A2/HSCs-P1: 0.0018, ALDH1A2/HSCs-P3: 0.001. 