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Synchronous cultures of MCF7 breast cancer cells were grown and treated with the following:

1. MCF7 → Treated with buffer (Control group).
2. MCF7.1 → Treated with an inhibitor of Cyclin D.
3. MCF7.2 → Treated with siRNA designed against Cyclin B1.

After treatment, the cells were stained and sorted using flow cytometry. The relative amount of DNA in each of the three phases of the cell cycle (G1, S, G2/M) was plotted against the number of cells, as shown in the provided graphs (A, B, C, D).

Which one of the following options correctly represents the cell cycle states of MCF7, MCF7.1, and MCF7.2?

Correct option is B

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Step 1: Understanding the Flow Cytometry Plots

• G1 Phase (Low DNA content, Peak at 1 unit DNA content)
• Indicates cells are arrested before DNA replication.
• S Phase (Intermediate DNA content)
• Represents cells actively replicating DNA.
• G2/M Phase (High DNA content, Peak at 2 units DNA content)
• Indicates cells preparing for mitosis or undergoing division.

Step 2: Identifying the Control Group (MCF7 - Buffer Treated)

• MCF7 is the control group, meaning its cell cycle profile should show a normal distribution of G1, S, and G2/M phases.
• Graph C represents a normal cell cycle pattern.
• Thus, MCF7 corresponds to Graph C.

Step 3: Effect of Cyclin D Inhibition (MCF7.1)

• Cyclin D promotes the transition from G1 to S phase.
• Inhibiting Cyclin D should cause G1 arrest, meaning most cells accumulate in G1 with a reduction in S-phase and G2/M cells.
• Graph A shows a strong G1 arrest, which matches this expectation.
• Thus, MCF7.1 corresponds to Graph A.

Step 4: Effect of Cyclin B1 Knockdown (MCF7.2)

• Cyclin B1 is essential for the G2/M transition.
• Inhibiting Cyclin B1 should cause G2/M arrest, meaning cells accumulate at G2/M with fewer in G1 and S phase.
• Graph D shows a G2/M block, meaning cells are arrested in the G2/M phase.
• Thus, MCF7.2 corresponds to Graph D.