A dpn enhancer and an Hsp70 basal promoter are fused upstream of a single copy of a 250bp element from the hb intron (this element is both necessary and sufficient for relocation of the hb gene to the nuclear lamina during neuroblast development), followed by sequences encoding the transmembrane domain of Hsap\CD4 followed by a tandem dimer composed of a copy of EGFP and a copy of GFP.