The highest levels of Ecol\lacZ geneexpression are found in embryos, pupae, and third instar imaginal discs.In embryos, expression is first detected at 3 hrs of development and bygastrulation, is prominent in the neurogenic ectoderm. During germ bandextension, expression is seen in alternating domains of high and lowexpression along the anterior-posterior axis. By the early germ bandextended stage, expression is restricted to the neurogenic region. DuringCNS development, expression is higher in neuroblasts than in epidermalprecursor cells. Expression is later seen in regions of ectoderm that willgive rise to the PNS. In 3rd instar larvae, reporter gene expression isobserved in the optic lobes, the ventral nerve cord, and in scatteredcells in the imaginal discs. Expression in the eye disc (predominantly inphotoreceptor cell R8) and in the wing disc (in sensory bristleprecursors) was described in detail. Ectopic expression of Ecol\lacZ was seenin wing discs derived from homozygous acHw-49c or acHw-1 females.