Overexpression

Overexpression refers to the condition in which a gene or its encoded product is expressed at higher-than-normal levels. In genetics and molecular biology, expression levels are typically compared to a reference state such as wild-type tissue, untreated controls, or baseline measurements. Overexpression can involve endogenous genes that are upregulated or exogenous genes introduced by experimental manipulation.

Causes of overexpression include gene amplification, regulatory mutations that increase transcription or RNA stability, chromosomal rearrangements, or the use of strong constitutive promoters in expression constructs. In laboratory settings, overexpression is commonly achieved by transfecting cells with plasmids or using viral vectors that drive robust transcription, sometimes with inducible systems to control timing and magnitude.

Applications of overexpression studies include functional characterization of proteins, production of recombinant proteins for research or industrial use, and the creation of cellular or organismal disease models to investigate mechanisms and potential therapies.

Biological consequences vary by context but can include enhanced protein activity, altered signaling pathways, dominant phenotypic effects, toxicity, protein misfolding, or endoplasmic reticulum stress. In disease, overexpression of oncogenes, receptors, growth factors, or transcription factors is linked to uncontrolled proliferation, survival advantages, and therapy resistance.

Measurement and interpretation rely on techniques such as quantitative PCR, RNA sequencing, and protein assays, with expression levels normalized to reference genes. It is important to distinguish overexpression from physiologically relevant upregulation, as non-physiological levels can produce artifacts that complicate data interpretation.