Choosing epithelial and junction antibodies: what a ck19 antibody identifies that a pan-keratin reagent cannot, why an e-cadherin antibody and a cdh1 antibody are the same target under two names, what a zo1 antibody reports about a tight junction, and the membrane pattern that is its own control

Choosing and reading these markers

1. Know that keratin subtypes are informative and pan-keratin is not. A specific keratin marks a subset of epithelia and is used to distinguish lineages and ducts; a pan-keratin cocktail confirms epithelial identity and no more. Choose from the question, and state which reagent produced a result.
2. Recognise that E-cadherin and CDH1 are one protein. They are the protein name and the gene name for the same target, and catalogue entries use both. Reagents against different domains behave differently after fixation, so compare on the epitope rather than on the naming.
3. Read a tight junction protein as a continuous line. A junctional protein should appear as a continuous line at cell borders in an intact monolayer, and breaks in that line are the informative result in barrier experiments. Cytoplasmic staining of a junction protein means either disassembly or a failed stain, and the control tells you which.
4. Use the pattern as the specificity control. Membrane and junctional proteins have unmistakable patterns. A stain that is the right intensity in the wrong pattern is a warning that costs nothing to notice and is the fastest check available on these targets.
5. Match fixation to the junction. Junctional epitopes are sensitive to fixation and to permeabilisation, and methanol and aldehyde protocols preserve them differently. Test both on a confluent monolayer known to have intact junctions before interpreting anything.

Barrier experiments need more than a stain

Junction morphology and barrier function are different measurements and can disagree. A transepithelial resistance reading or a tracer flux assay measures the barrier; the stain shows where the protein is.

Report both where the claim is about barrier integrity. A study resting on junctional staining alone is describing a picture rather than measuring a function.

Change of state readouts

Loss of an epithelial junction marker with gain of a mesenchymal filament marker is the classic transition readout, and both halves are needed. A single marker moving is not a transition, and neither marker alone is diagnostic.

Quantify per cell rather than per field, because these transitions are usually partial and heterogeneous, and a field average hides exactly the heterogeneity that is the biology.

Common questions

Are e-cadherin and cdh1 different targets?

No, they are the protein and gene names for the same molecule, and suppliers list both. What differs between products is the epitope domain, which changes how they behave after fixation and whether they work on intact cells.

Why is my junction protein stain cytoplasmic?

Either the junctions have genuinely disassembled, which is often the result you are looking for, or the fixation and permeabilisation are wrong. A confluent untreated monolayer stained alongside distinguishes the two immediately.

Should I use a specific keratin or a pan-keratin cocktail?

A specific keratin when the question is which epithelial lineage or which duct compartment. A pan-keratin cocktail when the question is only whether the cells are epithelial at all.

What is the quickest specificity check on these markers?

The pattern. A junction protein should draw a line at cell borders and a keratin should fill a cytoplasm. Right intensity in the wrong pattern is a failed stain whatever the datasheet says.

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