Dear Zaynab

Are your cells fixed? In order to use PI to comment on cell cycle status, you need to permeabilize fixed cells since PI cannot passively enter intact cells and bind DNA. But if you permeabilize cells then the PI/Annexin measurements are inconclusive. Hence, for this exact dataset, I would not recommend to use PI histogram to infer about cell cycle status. In a different reaction with fixed and permeabilized cells you can surely use PI to study cell cycle status of your cell population.

Good luck

Hi Zaynab

You can not make any conclusion with P1 unless you permeabilized the cell as suggested by Ms. Lahree. here is the protocol which may help you to estimated the cell population at various cell cycle stages (i.e G1, S, G2-M etc).

"harvest the cells and fixed in 70% ethanol for 2 h at 4°C. After incubation, wash and further incubated with 0.02 mg/ml propidium iodide (PI) along with DNase free RNase (1 mg/ml) for 30 min and run flow

Good luck