ZHENG L, LIU J-Z, Hu Y-W, ZHONG T-Y, XIONG S-L, WANG W, WANG Q. Simulated microgravity, erythroid differentiation, and the expression of transcription factor GATA-1 in CD34+ cells. Aviat Space Environ Med 2011; 82:513-7. Introduction: The microgravity environment of spaceflight leads to a series of changes in he human blood system. The aim of the present study was to examine the influence of simulated microgravity on the differentiation of CD34(+) cells and to explore whether transcription factor GATA-1, required for the terminal differentiation of committed erythroid progenitor cells, is involved in this process. Methods: CD34(+) cells were cultured in the simulated microgravity conditions created by a rotary cell-culture system (RCCS). The effects of simulated microgravity on the differentiation and apoptosis of CD34(+) cells were analyzed using flow cytometry and propidium iodide (PI) staining, respectively Expression of GATA-1 mRNA in CD34(+) cells was determined by real-time quantitative PCR. Results: In the RCCS group, GlyA(+) (glycophorin A) expression was lower and CD33(+) expression higher than in the 1-g liquid control group (22.21% +/- 3.02% and 60.05% +/- 3.08%, vs. 52.12% +/- 1.92% and 18.87% +/- 1.41%, respectively). The proportion of differentiated cells in the 1-g methylcellulose group (GlyA(+)% = 54.39% +/- 2.86%, CD33(+)% = 21.09% +/- 3.19%) was similar to that in the 1-g liquid control group. As shown by real-time quantitative PCR, the relative expression of GATA-1 mRNA in the RCCS group was only 20% of that in the 1-g control group. Conclusions: The differentiation of CD34(+) cells, and especially erythroid differentiation, was inhibited by simulated microgravity by a mechanism that appears to involve the suppression of GATA-1 mRNA expression. The results of this study may be useful in understanding the critical effect of simulated microgravity on the pathogenesis of space anemia.