EcollacZ expression in first, second,and third instar larvae and adults is abundant in most muscles. In thirdinstar wing imaginal discs, expression is confined to the SMCs, as well asmore differentiated cells of the PNS. Punctate expression is also seen inleg and antennal imaginal discs and in differentiating photoreceptorcells. In adults, the most conspicuous expression is seen in the IFM ofthe thorax and in muscles of the head around the proboscis. Neurons orsupport cells of the PNS of the head are stained strongly, includingantennal neurons and neurons of the maxillary palps. In legs of pharateadults, EcollacZ expression is most abundant in hair plates, campaniformsensilla, and tactile and multimodal organs.

The expression pattern of theEcollacZ^nrm-A37 enhancer trap line is similar to EcollacZ^neur-A101 but initiateslater in the campaniform SMCs and is limited to a single cell, thetormogen, in adults. Expression is seen in the ectopic sensilla that arisein the Hairy wing class of ac mutans, in other ac mutants and in hmutants.

Earliest detectable expression is at stage 7 in the head region, restricted to two bilateral clusters of 10-15 contiguous epidermal cells; during stage 8 a second set of clusters appears in the head region. At stage 9, small clusters of continguous epidermal cells can be detected in the body segments. In late embryos, expressed in all known peripheral neurons; a small number of non-neuronal cells also labelled, including one or more support cells of the external sense organs. In wing discs, expression is observed in a small number of dispersed cells in the regions of developing sensory organs.