Markerexpression

Marker expression refers to the presence and quantified level of molecular markers used to identify cell types, states, or biological processes in biological samples. Markers can be proteins, RNAs, or other molecules. In practice, marker expression is assessed to classify cells, track lineage, or infer functional status. Commonly used markers include cell surface proteins such as CD4, CD8, CD34, and CD45; intracellular proteins like GFAP or NeuN; and transcription factors such as Oct4 or Sox2. Nucleic acid markers include specific mRNA transcripts detected by RT-qPCR or RNA sequencing.

Techniques that measure marker expression include flow cytometry and mass cytometry (CyTOF) for single-cell protein analysis; immunohistochemistry and immunofluorescence for spatial visualization in tissues; in situ hybridization for RNA localization; and sequencing-based approaches that quantify transcript levels. All methods rely on appropriate controls, standardized workflows, and proper data normalization to enable comparison across samples.

Interpretation of marker expression is context-dependent and can vary with tissue type, developmental stage, environmental conditions, and technical factors. Researchers often compare expression to negative or reference populations and use panels of multiple markers to increase specificity, as single markers may be shared across cell types. Marker panels help define cell identities, states, or functional properties, while recognizing that heterogeneity exists within populations.

Applications span immunology, cancer biology, developmental biology, and stem cell research. Marker expression informs diagnostics, prognostics, and treatment decisions, such as identifying immune subsets or characterizing tumor phenotypes. Limitations include dynamic expression changes, overlapping marker patterns between lineages, and potential technical artifacts that require careful experimental design and interpretation.