The expression disruption system. (A) Representation of a genomic landscape composed of two enhancers (gray boxes) that drive expression of their target gene in the eye and hindbrain (gray pattern in embryo). (B) An ED insertion in this genomic landscape. ED is composed of two enhancer traps, one that has GFP (green box) as a reporter gene and the other RFP (red box). An insulator is present in between these two enhancer traps (purple box). Two loxP sequences (yellow triangles) flank the RFP enhancer trap and the insulator. In this insertion, the upstream enhancer is detected exclusively by the GFP enhancer trap cassette, and the downstream is detected only by the RFP cassette, resulting in the nonoverlapping expression of these two reporters (green and red patterns in the lower embryo). The block of the upstream enhancer by the insulator results in a regulatory mutation (higher embryo).
