Cell cycle assay
COLD
Cells were harvested and fixed in 70% cold ethanol and stored at 4 °C overnight. The next day cells were centrifuged at 2500 rpm for 5 min. After washed with PBS, cell pellets were treated with RNase A and stained with PI at 37 °C for 30 min in the dark. The cell cycle was assessed with flow cytometry (Beckman Coulter).