Identification of “anchoring genes ” in the promoter- upstream region of the Drosophila Abd-B domain

The Abd-B gene determines the segmental identity of four different abdominal segments (from the 5th to the 8th) through the action of extensive segment-specific cis-regulatory regions (iab-5, iab-6, iab-7, iab-8). Although these regulators are located many kilobases away the promoter, physical contact occurs between them through the looping out of the interven-ing DNA sequences. Genetic studies gave evidence that regulatory interactions between promoter and enhancer elements can be formed not only in cis but in trans, as well, between non-continuous DNA molecules. These trans-interactions depend on the physical proximity of homologous chromosomes. Taking advantage of this phenomenon, called “transvection”, we have tried to identify genes that help to anchor distant enhancers to the Abd-B gene