Figure 1. Schematic of the reporter system used in this study.

All constructs contained the vgBE enhancer flanked by FRT sites, a minimal hsp70 promoter flanked by loxP sites, an eGFP coding sequence, and either zero, one or two gypsy insulators (A). Differential Interference Contrast (DIC)-GFP overlay of a 3^rd instar wing disc showing the expression pattern of the vgBE along the dorsal-ventral (D/V) boundary, particularly within the hinge and wing margin (B). Communication in trans between a functional enhancer (“promoterless”) on one homolog and a functional promoter (“enhancerless”) on the other homolog might be facilitated by trans interactions between flanking gypsy insulators, leading to expression only from the “enhancerless” homolog (C).