The pattern of enhancer trapexpression closely resembles that of dpn transcripts and protein exceptthat the EcollacZ expression is maintained for longer periods of time.Expression is first detected in a ubiquitous pattern in embryonic cycle12. A transient gap-rule pattern in cycle 13 is followed by a pair-rulestripe pattern. EcollacZ is expressed briefly in patches of neurectodermpreceding the first wave of neuroblast segregation and become restrictedto the neuroblasts before they delaminate. By 6 1/2-7 hr, all neuroblastshave delaminated and express EcollacZ. In the PNS weak expression in patchesof ectodermal cells is followed by strong expression in sensillumprecursors. Expression in neural precursors disappears soon after theydivide and reappears at later stages of nervous system development of theCNS and PNS as neurons begin to differentiate. Expression is also observedin neuroblasts, ganglion mother cells and neurons of the larval CNS and insensory neurons and their precursors in imaginal discs. In leg imaginaldiscs, expression is also observed in additional non-neuronal cells.