An organelle antibody is doing two jobs at once and they pull in opposite directions. It has to label a compartment reliably enough that its outline can be measured, and it has to be specific enough that a change in signal means a change in the compartment rather than a change in the protein it is aimed at. Almost every widely used marker fails the second job under some condition, because the proteins that identify a compartment are also the proteins a cell adjusts when that compartment is under load, and a fixation chosen for one marker routinely destroys the epitope of the next.
What a mitochondrial marker antibody reports besides location
Outer membrane proteins, inner membrane complexes and matrix proteins behave differently under stress: a cell that is losing mitochondria by autophagy loses the outer membrane signal first, while a cell that is remodelling the network keeps the protein and changes the shape. So a single antibody supports a statement about morphology and not about mass, and a statement about mass needs either two markers in different submitochondrial compartments or an independent measure. Choose the compartment deliberately and say in the method which one the antibody is in.
When a mitochondria antibody is the wrong tool entirely
For counting or for membrane potential, a dye beats an antibody: the antibody needs fixation, which fixes the morphology at one instant and cannot report function at all. The antibody is the right tool where the question is which protein is present, where the sample is already fixed, or where the signal has to survive permeabilisation for another stain. Deciding this before the experiment saves a set of images that cannot answer the question they were taken for.
Reading an er marker antibody against the secretory pathway
The endoplasmic reticulum is continuous with the nuclear envelope and adjacent to the Golgi, so a marker with modest specificity produces an image that looks like the whole secretory system. A luminal chaperone and a membrane protein give different outlines of the same compartment, and the chaperone is also induced by stress, which means an increase in signal can be induction rather than expansion. Where the experiment perturbs folding, pair the marker with one that is not stress responsive.
Why autophagosome markers are read as a flux, never as a count
The structures being labelled are transient by definition: a marker that accumulates can mean more are being made or fewer are being cleared, and those are opposite conclusions. The measurement that distinguishes them compares the marker with and without a block on the degradation step, which is why a single image of labelled structures supports no claim about autophagy. The lipidated form of the standard marker also runs differently on a gel from the unmodified one, which is what makes the blot informative where the image is not.
Exosome markers, and the exosome marker a preparation should carry
Small vesicle preparations are judged on the presence of membrane and cytosolic proteins expected in them and the absence of markers of the compartments they are often contaminated with. That is the whole of the assessment: a preparation with the expected proteins and no evidence of the contaminants is a vesicle preparation, and one that reports only the expected proteins has shown half of the result. Both halves belong in the method, and so does the separation technique, because the contaminant profile follows the technique rather than the tissue.
Fixation is the choice that decides all of them
Aldehyde fixation preserves structure and hides some epitopes; organic solvent fixation exposes them and removes lipid, which distorts membrane compartments. So a panel across compartments is constrained by whichever marker is fussiest, and the honest way to run it is to validate each antibody under the single fixation the panel will use rather than under its datasheet's. Where two markers cannot share a fixation, they cannot share an image, and a colocalisation claim across two protocols is not a colocalisation claim.
Questions people ask about lysosome marker antibody
Can one antibody mark a compartment across cell types?
Often, and the failures are specific rather than general: expression of the identifying protein varies by cell type and differentiation state, so a marker that is bright in one line can be faint in another without the compartment being smaller. Check a positive control of the actual cell type before reading an absence as biology.
Why does my colocalisation change with the fixation?
Because both the structure and the epitopes change. Solvent fixation removes lipid and collapses membranes, aldehyde fixation cross links and can hide a binding site, and the apparent overlap of two compartments moves with both. Fix one way for a whole experiment and report which.
Do I need a marker antibody if I have a fluorescent protein fusion?
Usually yes, as a check rather than a replacement. A fusion reports where the tagged protein is, which is not always where the compartment is, particularly when it is overexpressed. One marker antibody on a subset of the samples is enough to show that the fusion and the compartment agree.