Housekeeping gene western blot loading controls: choosing one that is actually invariant, why a gapdh antibody and a beta actin antibody disagree in some tissues, and when total protein normalisation is the better answer

Choosing and validating a control

1. Verify invariance in your own system. The standard housekeeping proteins vary with cell cycle, confluence, hypoxia, differentiation and many treatments. Before adopting one, run your treatment series and confirm the candidate does not change. Inheriting a control from a published paper in a different system is how normalisation goes wrong quietly.
2. Match the abundance to the target. A control far more abundant than the target saturates at exposures where the target is barely visible, so the two cannot be quantified on the same blot. Choose a control of comparable abundance, or image the two separately with appropriate exposures.
3. Check the molecular weight separation. The control must resolve clearly from the target and from any non-specific band. A control running close to the target complicates stripping, reprobing and multiplexed detection.
4. Stay inside the linear range. Densitometry is only meaningful where signal is proportional to protein, and film and bright bands both saturate. Run a loading series once to establish the linear range for both target and control, and work inside it.
5. Consider total protein normalisation. Staining the membrane for total protein normalises to everything loaded rather than to one protein that may itself respond. It avoids the invariance problem entirely and has become the preferred approach where the target's abundance allows it.

When housekeeping controls mislead

Treatments that alter metabolism, cytoskeleton, proliferation or differentiation are precisely the treatments that move the conventional controls, and those are also the treatments laboratories study most. The result is a normalisation that removes part of the effect or manufactures one.

Where a control does move with treatment, the honest options are to change control, move to total protein normalisation, or report unnormalised data with the loading shown. Choosing the control that gives the expected answer is not among them.

Practical detection points

Multiplexed fluorescent detection lets target and control be imaged in separate channels on one blot, which avoids stripping and reprobing and generally gives cleaner quantitation than chemiluminescence with film.

Whichever detection is used, record exposures and keep the raw images. Quantitation from a figure-ready image with adjusted contrast is not quantitation.

Common questions

Which housekeeping gene should I use as a western blot control?

One you have shown does not change under your treatment, at an abundance comparable to your target and resolving clearly from it. The conventional choices all vary under common conditions, so the validation matters more than the choice.

Is total protein normalisation better?

Often, because it normalises to everything loaded rather than to one protein that may itself respond to the treatment. It avoids the invariance problem and is generally preferred where the target's abundance allows.

Why does my loading control look identical in every lane?

Frequently because it is saturated. A highly abundant control imaged at an exposure suited to a faint target will look uniform regardless of loading, which makes it useless as a control.

How do I know I am in the linear range?

Run a loading series once for both target and control and find where signal stops being proportional to protein. Quantify only inside that range.

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