The dare gene: steroid hormone production, olfactory behavior, and neural degeneration in Drosophila

Steroid hormones mediate a wide variety of developmental and physiological events in insects, yet little is known about the genetics of insect steroid hormone biosynthesis, Here we describe the Drosophila dare gene, which enc odes adrenodoxin reductase (AR), In mammals, AR plays a key role in the syn thesis of all steroid hormones. Null mutants of dare undergo developmental arrest during the second larval instar or at the second larval molt, and da re mutants of intermediate severity are delayed in pupariation. These defec ts are rescued to a high degree by feeding mutant larvae the insect steroid hormone 20-hydroxyecdysone. These data, together with the abundant express ion of dare in the two principal steroid biosynthetic tissues, the ring gla nd and the ovary, argue strongly for a role of dare in steroid hormone prod uction. dare is the first Drosophila gene shown to encode a defined compone nt of the steroid hormone biosynthetic cascade and therefore provides a new tool for the analysis of steroid hormone function. We have explored its ro le in the adult nervous system and found two striking phenotypes not previo usly described in mutants affected in steroid hormone signaling. First, we show that mild reductions of dare expression cause abnormal behavioral resp onses to olfactory stimuli, indicating a requirement for dare in sensory be havior. Then we show that dare mutations of intermediate strength result in rapid, widespread degeneration of the adult nervous system.