A 3.8kb HindIII fragment of the ctregulatory region fused to a minimal Hsp70 promoter drives expression ofEcollacZ in embryonic and larval tissues. In the embryonic central nervoussystem (CNS), EcollacZ expression is visible in 4 cells per segment. In theembryonic peripheral nervous system (PNS), EcollacZ is expressed in theantenno-maxillary organs, the hypophysis, and the epiphysis. The ventralend of fascicles which carry axons from the PNS into the ganglia of theCNS express EcollacZ in both embryos and late third instar larvae. A subsetof cells in the internal portion of the posterior spiracles of the embryoexpress EcollacZ. EcollacZ staining in the Malpighian tubules is weak.