Ectopic expression

Ectopic expression is the expression of a gene in a tissue where it is not normally expressed. Ectopic is a word used with a prefix, ecto, meaning “out of place.” Ectopic expression also refers to the expression of a gene at a point in the cell cycle or in an organism's development when it is not normally expressed. This can be caused by a disease, or it can be artificially produced as a way to help determine what the function of that gene is. The term ectopic expression is predominately used in studies using metazoans, especially in Drosophila melanogaster for research purposes.

Although ectopic expression can be occurred by a natural condition (i.e. defects in gene expressions), it can be artificially produced to help determine what the function of that gene is using overexpressing or misexpressing the genes by UAS-Gal4 system. In D. melanogaster, overexpression or misexpression are used to perform genetic screens to identify gene products involved in specific cellular or developmental processes. Ectopic expression using these techniques is a useful tool because phenotypes occurred by these abnormal expressions in a tissue where is not normally expressed are much easily distinguishable than the expressions in another tissue where is usually expressed. In addition, these phenotypes by ectopic expression demonstrate the function of a gene of interest.

Paired box protein Pax-6 (Pax6) in humans is a transcription factor, which is a main regulatory gene of eye and brain development. Ectopic expression of Drosophila homolog eyeless (ey) has been used to identify roles of Pax-6 in humans. Using tissue specific UAS-Gal4 system, ey can be induced on the legs, wings, halters and antennae of the transgenic flies to demonstrate that functions of ey.

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