The role of carcinine in signaling at the Drosophila photoreceptor synapse.

The Drosophila melanogaster photoreceptor cell has long served as a model system for researchers focusing on how animal sensory neurons receive information from their surroundings and translate this information into chemical and electrical messages. Electroretinograph (ERG) analysis of Drosophila mutants has helped to elucidate some of the genes involved in the visual transduction pathway downstream of the photoreceptor cell, and it is now clear that photoreceptor cell signaling is dependent upon the proper release and recycling of the neurotransmitter histamine. While the neurotransmitter transporters responsible for clearing histamine, and its metabolite carcinine, from the synaptic cleft have remained unknown, a strong candidate for a transporter of either substrate is the uncharacterized inebriated protein. The inebriated gene (ine) encodes a putative neurotransmitter transporter that has been localized to photoreceptor cells in Drosophila and mutations in ine result in an abnormal ERG phenotype in Drosophila. Loss-of-function mutations in ebony, a gene required for the synthesis of carcinine in Drosophila, suppress components of the mutant ine ERG phenotype, while loss-of-function mutations in tan, a gene necessary for the hydrolysis of carcinine in Drosophila, have no effect on the ERG phenotype in ine mutants. We also show that by feeding wild-type flies carcinine, we can duplicate components of mutant ine ERGs. Finally, we demonstrate that treatment with H(3) receptor agonists or inverse agonists rescue several components of the mutant ine ERG phenotype. Here, we provide pharmacological and genetic epistatic evidence that ine encodes a carcinine neurotransmitter transporter. We also speculate that the oscillations observed in mutant ine ERG traces are the result of the aberrant activity of a putative H(3) receptor.

Accelerated accumulation of misfolded prion protein and spongiform degeneration in a Drosophila model of Gerstmann-Sträussler-Scheinker syndrome.

Prion diseases are CNS disorders that can occur in sporadic, infectious, and inherited forms. Although all forms of prion disease are associated with the accumulation of pathogenic conformers of the prion protein, collectively termed PrP(Sc), the mechanisms by which PrP(Sc) molecules form and cause neuronal degeneration are unknown. Using the bipartite galactosidase-4-upstream activating sequence expression system, we generated transgenic Drosophila melanogaster heterologously expressing either wild-type (WT) or mutant, disease-associated (P101L) mouse PrP molecules in cholinergic neurons. Transgenic flies expressing neuronal P101L PrP molecules exhibited severe locomotor dysfunction and premature death as larvae and adults. These striking clinical abnormalities were accompanied by age-dependent accumulation of misfolded PrP molecules, intracellular PrP aggregates, and neuronal vacuoles. In contrast, transgenic flies expressing comparable levels of WT PrP displayed no clinical, pathological, or biochemical abnormalities. These results indicate that transgenic Drosophila expressing neuronal P101L PrP specifically exhibit several hallmark features of human Gerstmann-Sträussler-Scheinker (GSS) syndrome. Because the rates of abnormal PrP accumulation and clinical progression are highly accelerated in Drosophila compared with the rates of these processes in rodents or humans, the P101L mutant may be used for future genetic and pharmacologic studies as a novel invertebrate model of GSS.