Complex organization of promoter and enhancer elements regulate the tissue- and developmental stage-specific expression of the Drosophila melanogaster Gld gene

The Drosophila melanogaster Gld gene has multiple and diverse developmental and physiological functions. We report herein that interactions among prox imal promoter elements and a cluster of intronically located enhancers and silencers specify the complex regulation of Gld that underlies its diverse functions. Gld expression in nonreproductive tissues is largely determined by proximal promoter elements with the exception of the embryonic labium wh ere Gld is activated by an enhancer within the first intron. A nuclear prot ein, GPAL, has been identified that binds the Gpal elements in the proximal promoter region. Regulation of Gld in the reproductive organs is particula rly complex, involving interactions among the Gpal proximal promoter elemen ts, a unique TATA box, three distinct enhancer types, and one or more silen cer elements. The three somatic reproductive organ enhancers each activate expression in male and female pairs of reproductive organs. One of these pa irs, the male ejaculatory duct and female oviduct, are known to be developm entally homologous. We report evidence that the other two pairs of organs a re developmentally homologous as well. A comprehensive model to explain the full developmental regulation of Gld and its evolution is presented.