AN EVOLUTIONARILY CONSERVED PALINDROME IN THE DROSOPHILA GLD PROMOTERDIRECTS TISSUE-SPECIFIC EXPRESSION

A conserved palindromic sequence (Gpal) in the promoter region of the Drosophila Gld directs expression of a heterologous reporter gene in t ransgenic flies to the anterior spiracular glands of third instar larv ae and to the ejaculatory bulb of adult males. The Gld gene is normall y expressed at high levels in the anterior spiracular glands but is no t expressed in the ejaculatory bulb of Drosophila melanogaster. Howeve r. Gld promoters from other Drosophila species contain the Gpal elemen t and express glucose dehydrogenase (GLD) in the adult male ejaculator y bulb. A gene fusion composed of the D. melanogaster Gld promoter and the lacZ gene is expressed in the anterior spiracular glands of trans genic larvae. Mutations of the Gpal sequence element in this gene fusi on block expression of beta-galactosidase in the anterior spiracular g land. Together these experiments demonstrate that Gpal is necessary an d sufficient for tissue-specific expression in the anterior spiracular glands. Based upon the tissue distribution and function of GLD, it is speculated that expression of GLD in the anterior spiracular glands r epresents the ancestral state and that GLD expression in other tissues arose as a fortuitous consequence of a shared combinatorial regulator y network.