At embryonic stage 15, hEcollacZ^hdc-B5 is expressed in two lateral anterior clusters of 6-7 cells, and a posterior cluster of 2-3 cells in the genital disc, reproducing the pattern of hdc transcipt expression.

The EcollacZ^hdc-B5 enhancer trapdrives EcollacZ expression in all imaginal cells. The earliest expression isin the stage 13 embryo, in imaginal neuroblasts, and in the precursors tothe prothoracic and leg disc primordia. The staining in the leg discprimordia intensifies by stage 15. Expression is also detected in thegenital disc primordia, the brain lobes, oesophageal ganglia,clypeo-labral, labial, and eye-antennal disc primordia. At stage 17,expression is also detected in the testis, lymph gland, and pericardialcells. In third instar larvae, EcollacZ expression continues to be detectedin the lymph gland, pericardial cells flanking the aorta, testis,eye-antennal disc, clypeo-labral disc, and the ventral prothoracic andmesothoracic discs. Third instar larval alimentary expression is seen inthe foregut and hindgut imaginal rings, and the midgut imaginal island.Imaginal tracheoblasts, dorsal prothoracic discs associated with theanterior spiracles, and spiracular histoblast nests express EcollacZ.