Ectopic misexpression

Reverse genetic approaches start with a sequence and attempt to identify a function for the gene. This can be done by using PCR-based screens on DNA from insertionally mutagenized populations, ectopic misexpression of the gene, and expression studies, e.g., with RT-PCR or microarray analyses. 

Lufkin et al. (1992) also used a homeobox gene promoter exchange to drive misexpression of the Hox-4.2 gene. The Hox-1.6 promoter was observed to extend the anterior transcription boundary, and this region of ectopic expression gave a number of abnormalities, including absence... 

The most dramatic illustration of the evolutionary conservation of homeobox genes comes from experiments that swap Drosophila and mammalian cognates and test for functional equivalence. McGinnis and co-workers have reported remarkable phenotypic similarities in flies that misexpress Drosophila homeobox genes or their mammalian counterparts. Indeed, this ectopic expression assay in Drosophila indicates that the Drosophila and cognate mammalian homeobox proteins are essentially functionally identical. 

Kosbash T o put it more generally, if you do a misexpression experiment and get a behavioural consequence with this vector, it is impossible to distinguish whether it is because of up-regulation in the usual locations or because of ectopic expression in the new locations. This is due to the fact that the construct also expresses more heavily in the traditional clock cells. Therefore it could be the up-regulation in the traditional clock cells that leads to the behavioural consequences. 

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