Simulated microgravity inhibits proliferation of murine HSPCs. A) Expression of lineage-specific markers CD3ε, TCR-β, B220, CD11b, F4/80, and CD11c in murine HSPCs after 12 d of culture under normal and simulated microgravity conditions. B) Growth curve of HSPCs by living-cell counting method during 12 d of culture under normal gravity and simulated microgravity conditions. C) HSPCs after 12 d of culture under normal and simulated microgravity conditions. D) Percentages of Ki67+ HSPCs after culture under normal ground control and simulated microgravity conditions for 12 d. µ-g, simulated microgravity; 1-g, normal gravity. **P < 0.01.