Question

Cancer cells display a high level of heterogeneity in the expression of TP53 protein. Which of the following techniques can be directly used to determine the intra-tumoral heterogeneity of TP53 expression in a given tumor sample, without resorting to additional cell separation techniques?

• A. Immunoblotting
• B. Flow cytometry
• C. ELISA
• D. Quantitative RT-PCR

Hint:

Look for the technique that measures TP53 in each individual cell, not one averaged bulk reading, without needing to separate cells first.

Answer 1

The Correct Option is B

The question asks which single technique can show cell-to-cell (intra-tumoral) differences in TP53 protein levels within one tumor sample, without first sorting or separating the cells into subgroups. The method must look at individual cells one at a time, not just give one averaged reading for the whole sample.

1. Immunoblotting (Western blot): this technique lyses the whole tissue sample together and measures total TP53 protein in the resulting mixture. It gives one average band intensity for the entire population of cells, so any heterogeneity between individual cells is lost, all cells are blended into a single lysate before measurement.
2. Flow cytometry: this technique keeps cells intact and suspended, stains each one for TP53 (usually after fixation and permeabilization) with a fluorescent antibody, then passes the cells one by one through a laser detector. The instrument records a separate fluorescence value for every single cell, so the output is a full distribution (histogram) of TP53 levels across the population, directly showing which cells express more or less TP53, without needing to physically separate any cells beforehand.
3. ELISA: like immunoblotting, ELISA is run on a bulk lysate or homogenate of the tumor sample in a single well of a plate. It reports one overall concentration value for the whole sample, again hiding cell-by-cell variation.
4. Quantitative RT-PCR: standard qRT-PCR is done on RNA extracted from the whole tissue sample together, giving one average expression value for the TP53 transcript across all cells pooled. It cannot resolve differences between individual cells unless combined with single-cell isolation methods, which the question rules out.

Flow cytometry is the only listed method that reads out a per-cell signal directly from the mixed population, revealing intra-tumoral heterogeneity in TP53 expression without any extra cell-separation step.

Let's summarize:

• Immunoblotting, ELISA, and standard qRT-PCR all give bulk, averaged readings that erase cell-to-cell differences.
• Flow cytometry measures each cell's TP53 signal individually as it passes the detector, directly capturing heterogeneity.

The correct answer is flow cytometry, option (B).