Box 1. Overexpression vs. misexpression vs. ectopic expression.

These terms are often used interchangeably and the distinctions between them typically are not explicitly defined.
The term “overexpression” predominates in studies involving unicellular organisms, implying increased expression beyond the norm, without any knowledge of the normal expression levels or pattern.
The terms “misexpression” and “ectopic expression” predominate in studies using metazoans, implying expression of a gene in a cell type or developmental stage or condition in which it normally is not expressed. Because the underlying genetic principles are identical, the term overexpression is used in this review, as it does not presuppose any assumptions about the basal expression of the gene.
The terms misexpression and ectopic expression might be more appropriate for targeted overexpression studies when details of the expression pattern are known.