Notch1 antibody and other signalling antibodies: choose by the fragment the pathway makes

Choosing and validating

1. Decide which species of the protein answers your question. Full length receptor, cleaved fragment, phosphorylated form or a conformational state are different analytes. For cleavage activated pathways the fragment is the signal, and an antibody against the extracellular region will never report it.
2. Match extraction to the compartment. Membrane and nuclear proteins need extraction conditions that a standard lysis buffer does not provide, and a target that appears absent is frequently a target that stayed in the pellet. Fractionate when the compartment matters.
3. Choose fixation for the epitope, not for the tissue. Cross linking fixation masks many epitopes and requires retrieval; some epitopes survive only in alcohol fixation or in frozen sections. The application listed on the datasheet is a starting point rather than a guarantee.
4. Demand validation evidence in your application. A blot on an overexpression lysate does not validate immunohistochemistry. Look for knockout or knockdown validation, and where it is absent, run a reduction control yourself before building on the reagent.
5. Record clone and lot as part of the method. Two clones against the same target are different reagents and frequently give different distributions. A protocol that names only the target is a protocol that will not reproduce when the catalogue changes.
6. Include a biological control that moves the signal. A treatment or genotype expected to change the target is worth more than any isotype control. It shows the reagent tracks the biology rather than something constant.

One target, several analytes

Most disappointment with signalling antibodies comes from treating the gene name as the specification. The same gene produces a precursor, a mature form, cleavage products and modified variants, and a reagent is raised against a region that may be present in some of them and absent from others.

Read the immunogen region against the domain structure before buying. It takes ten minutes and it explains in advance most of what would otherwise be a month of troubleshooting.

Controls that actually control

An isotype control shows what a non specific antibody of that class does; it does not show that your antibody is specific. Reduction of the target, competition with the immunogen peptide, or a tissue known not to express it are the controls that carry weight.

Run one of them once per reagent, keep the image, and the reagent becomes something the laboratory can rely on rather than argue about.

A notch2 antibody and the paralogue it sits beside

The four receptors share a domain architecture, so a notch2 antibody has to be raised against a region that differs, most often the intracellular domain or a paralogue specific epitope. Cross reactivity data against the other three is the line worth reading. Where the biology is about one receptor in a tissue that expresses several, a knockdown lane is what makes the band evidence.

A notch3 antibody and the vascular reading of it

NOTCH3 is enriched in mural cells and is the gene behind CADASIL, so a notch3 antibody is often bought for a vessel wall stain rather than for a signalling blot. The extracellular domain accumulates in that disease, which means an antibody against it and one against the cytoplasmic tail report different things in the same section. The datasheet's epitope position decides which question is being asked.

A dll3 antibody and a target that is mostly intracellular

DLL3 is an inhibitory ligand that sits largely in the Golgi and endosomes rather than on the surface, so a dll3 antibody used for flow cytometry on unpermeabilised cells reads low even where the protein is abundant. That is the whole difficulty in using it as a surface target. Permeabilised staining, a section, or a blot with a positive control line is where the protein is actually seen.

A dll4 antibody and a dll1 antibody on the activating ligands

The activating ligands are expressed on the signal sending cell, so the useful image is two channels showing which cell carries the ligand and which carries the receptor. A dll4 antibody is read in endothelium, where it marks tip cells, while a dll1 antibody is read in the neighbouring lineages. Both are transmembrane and glycosylated, so apparent mass on a blot sits above the calculated value.

A dlk1 antibody and a ligand that does not signal the usual way

DLK1 carries the ligand architecture without activating the canonical pathway, which is why a dlk1 antibody is bought as a lineage and imprinting marker rather than as a pathway reagent. It is shed as a soluble fragment, so an antibody against the extracellular domain may report medium as well as cells. Whether the clone sees the membrane form, the soluble form or both is the question for the supplier.

An ascl2 antibody as a pathway output rather than a component

Target gene products are the honest readout of a pathway, since receptor levels move little while outputs move a lot. An ascl2 antibody reports an intestinal stem cell transcription factor downstream of the pathway, so it belongs beside the receptor stain rather than instead of it. It is a nuclear protein of modest abundance, which makes a nuclear extract and a nuclear loading reference the preparation that works.

Common questions

Why does an antibody work on a blot and not on a section?

Because fixation and epitope accessibility differ completely. Denatured, linearised protein on a membrane presents epitopes that a cross linked tissue section hides, and retrieval conditions have to be optimised for each reagent.

How do I detect an activated receptor with a Notch antibody?

By detecting the species that activation produces, usually a cleaved fragment or a phosphorylated form, with a reagent raised against the neoepitope. Detecting total receptor tells you about expression, not activity.

Is knockout validation necessary?

It is the strongest available evidence and increasingly expected. Where no knockout exists, a knockdown with a clear signal reduction, or a peptide competition, is an acceptable substitute if documented.

Why does my nuclear factor show only cytoplasmic staining?

Frequently an extraction problem rather than biology. Nuclear proteins need a buffer that opens the nucleus, and standard whole cell lysis leaves much of the target in the insoluble fraction.

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