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July 10, 2026

Why Does My mRNA Target Have Ct 28 But Protein Is Undetectable?

A Ct of 28 is solidly in the "expressed" range — it's not a Ct 35 scraping the noise floor. So when your western blot comes back blank or your IF shows nothing, the instinct is to blame the antibody. And honestly? About half the time that instinct is right. But the other half involves real biology or qPCR artifacts that are worth understanding before you burn through three more antibody catalogs.

The short answer: mRNA abundance and protein abundance correlate poorly for many genes. Landmark proteogenomic studies (Schwanhäusser et al., 2011; Vogel & Bhatt, 2012) found that mRNA levels explain only about 40% of the variance in protein levels. Translational regulation, protein half-life, post-translational degradation, and secretion all drive the wedge between what qPCR tells you and what your protein detection assay shows. But there are also technical explanations — on both the qPCR side and the protein side — that you should rule out first.

Make Sure Your Ct 28 Actually Means What You Think It Means

A Ct of 28 is relative. If your reference gene (ACTB, GAPDH) is coming in at Ct 15, your ΔCt is 13, which means your target is roughly 8,000-fold less abundant than your housekeeping gene. That's low-to-moderate expression — detectable by qPCR but potentially below the sensitivity threshold of a western blot, especially for a protein without a great antibody.

Run the numbers: if your efficiency is ~100%, every Ct unit represents a 2-fold difference. A ΔCt of 13 means 2^13 = 8,192-fold less mRNA than your reference. Compare this to a gene you know you can detect by western — say a ΔCt of 6-8. That's the kind of quick sanity check that takes two minutes and saves you a week of troubleshooting the wrong assay.

Also verify the Ct is real:

If after all this your Ct 28 holds up as legitimate, target-specific mRNA signal, then the disconnect is either biological or on the protein detection side.

Biological Reasons mRNA Doesn't Become Detectable Protein

This is the part that frustrates people because it means no one made a mistake — the biology just doesn't cooperate.

Translational repression. miRNAs, upstream open reading frames (uORFs), and RNA-binding proteins can park an mRNA in a translationally silent state. The transcript is there, qPCR sees it, but ribosomes aren't making protein from it. This is especially common for tightly regulated genes: transcription factors, signaling molecules, and anything involved in cell cycle control. If your target is in one of these categories, check the literature for known translational regulation.

Protein half-life and degradation. Some proteins are made and immediately degraded — think polyubiquitinated targets headed for the proteasome. The mRNA is translated, but steady-state protein never accumulates to detectable levels. Classic examples include p53 in unstressed cells (mRNA present, protein constitutively degraded by MDM2) and many short-lived signaling intermediates. If you suspect this, try treating cells with MG132 or another proteasome inhibitor for 4-6 hours before harvesting and re-running your western.

Secretion. If your target is a secreted protein — cytokines, growth factors, matrix metalloproteinases — it won't accumulate intracellularly. You'll see the mRNA in your cell lysate but need to look at conditioned media for the protein. This catches people more often than you'd expect. Check the UniProt entry for your protein; if it has a signal peptide annotation, look in the supernatant.

Isoform mismatch. Your qPCR primers amplify a region shared by multiple transcript variants, but the dominant isoform in your cell type might produce a truncated protein that lacks the epitope your antibody recognizes, or a non-coding transcript variant. Check your primer binding sites against the RefSeq transcript variants for your gene on NCBI.

Cell-type or condition-specific translational control. A gene might be robustly translated in one tissue and translationally repressed in another, even with similar mRNA levels. This is well-documented for many neural genes and for genes under hypoxic translational control via eIF2α phosphorylation.

Technical Reasons on the Protein Detection Side

Before invoking complex biology, rule out the mundane stuff. Most "I see mRNA but no protein" stories in my experience end here.

The antibody doesn't work. This is the most common explanation, full stop. Antibody validation in the literature is inconsistent, and many commercial antibodies — particularly polyclonals — have batch-to-batch variability that would make a qPCR person cry. Troubleshooting steps:

  1. Use a positive control lysate. Order one from the antibody vendor or use a cell line known to highly express your target (check the Human Protein Atlas at proteinatlas.org — it has IHC and western data for thousands of proteins across cell lines).
  2. Try a second antibody targeting a different epitope. If two independent antibodies both fail, you're less likely to be dealing with a bad reagent.
  3. Verify the antibody works in your application. An antibody validated for IP may not work for western, and vice versa. Check the datasheet for application-specific validation.

Protein extraction conditions matter. Nuclear proteins won't be in a standard RIPA lysate if you're only collecting the soluble fraction. Membrane proteins may need detergent optimization (try 1% Triton X-100, or even 1% SDS with sonication). If your target is in an insoluble fraction, you'll miss it entirely with gentle lysis.

Sensitivity mismatch. A standard western blot detects proteins down to roughly low-nanogram range on membrane. qPCR can detect single-digit copies of mRNA. The dynamic range of qPCR (Ct 10 to Ct 38, ~2^28 or ~250 million fold) vastly exceeds the dynamic range of a western blot (~100-1,000 fold). A Ct of 28 for a modestly translated, rapidly degraded protein might simply be below the detection limit of western blotting but well within qPCR's range.

If sensitivity is the issue, consider:

Transfer and blotting issues. Large proteins (>150 kDa) transfer poorly, especially with semi-dry systems. Small proteins (<15 kDa) can blow through the membrane. If your target is at either extreme, optimize transfer time, methanol concentration, and membrane type (PVDF vs. nitrocellulose, pore size).

A Practical Decision Tree

When I hit this situation — decent Ct, no protein — I work through this in order:

  1. Verify qPCR specificity: melt curve, NRT control, gel of the PCR product. Is the Ct real?
  2. Calculate ΔCt. Is the target actually low-expression relative to your housekeepers?
  3. Confirm the antibody works with a positive control lysate or cell line.
  4. Check if the protein is secreted (look in conditioned media) or requires nuclear/membrane extraction.
  5. Increase western sensitivity — more protein, better substrate, longer exposure.
  6. If all technical checks pass, start considering translational regulation, proteasomal degradation (MG132 experiment), or isoform issues.

The key insight is that qPCR and western blot are measuring fundamentally different molecules with vastly different dynamic ranges. A Ct of 28 can be completely real and biologically meaningful at the mRNA level while the corresponding protein is genuinely absent or below detection. Neither assay is lying to you — they're just answering different questions.

When the Disconnect Is the Finding

Sometimes the mRNA-protein discordance isn't a problem to troubleshoot — it's the result. Post-transcriptional regulation is a major axis of gene control, and documenting that a gene is transcribed but not translated (or translated but rapidly degraded) in a specific context can be genuinely interesting. If you've done the technical controls and the disconnect holds, consider that your data might be telling you something worth following up on rather than something to fix.

If you're running the qPCR side of these experiments regularly and want to make sure your Ct values, efficiencies, and relative quantification are solid before you start comparing across assay platforms, VoilaPCR handles ΔΔCt calculations, efficiency corrections, and replicate QC automatically — so at least you know the mRNA data is airtight before you start debugging the western.

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