Synthetic Lethality Induced by a Strong <i>Drosophila</i> Enhancer of Expanded Polyglutamine Tract

Abstract

Proteins containing an expanded polyglutamine tract are neurotoxins. The expanded polyglutamine proteins influence a variety of cellular functions. In Drosophila the GMR-Gal4/UAS expression system has been widely used in an eye-based model to study human neurodegenerative diseases. This system has facilitated the isolation and characterization of abundant Drosophila genes that interact with the expanded polyglutamine proteins. We used the GMR-Gal4/UAS system to express three proteins containing an expanded polyglutamine tract, or an expanded polyglutamine tract alone. Doubling the dose of these proteins resulted in pupal lethality, indicating that these toxic proteins induced a sensitized condition that is prone to synthetic lethality. By using the GMR-Gal4/UAS system, we showed that a Drosophila gene interacts with three expanded polyglutamine proteins to induce a synthetic lethal phenotype. We further demonstrated that the synthetic lethality was mediated through the toxic expanded polyglutamine tract. Our study raises a possibility that conventional genetic screens may not recover synthetic lethal alleles, which are presumably stronger interacting alleles than the currently known modifiers of an expanded polyglutamine tract, due to synthetic lethality.

Synthetic Lethality Induced by Toxic Polyglutamine Tract II: A Survey in Drosophila

“…When induced by the GMR-Gal4/UAS system in the eyes, Dikar's expression caused compound external eye defects, including a rough surface and disrupted arrays of the bristles on the eye surface [22]. In addition, coexpressing Dikar and an expanded polyglutamine tract induced synthetic lethality at pupal stages.…”

“…Flies were cultured on standard corn/agar media at 25˚C, unless otherwise stated. The strains and alleles used in this study were obtained from the Bloomington Drosophila Stock Center and other sources as described previously [22]. Through meiotic recombination, we generated a set of stocks, each of which contains a Chromosome 2 carrying two transgenes.…”

“…For survival analysis, a genetic cross was set up to generate two types of progeny at equal frequency: one carrying a genotype of interest and the other, a sibling genotype, carrying a CyO balancer chromosome as an internal control group, similar to those described previously [22]. If the viability of a genotype is unaffected by either expressing a transgene, or by coexpressing two transgenes, the number of the progeny should be evenly divided by the two genotypes, which are recognized as carrying straight wings or carrying curly wings (determined by the dominant Cy mutation on the CyO balancer).…”

“…To generate alleles that could be overexpressed by using GMR-Gal4/UAS, a genetically engineered P element, XP, was used [22] [23]. Each end of the XP element contains an UAS-expression construct that is orientated in the outward direction, so it is capable of overexpressing flanking endogenous genes.…”

“…Recently, we came across a synthetic lethality phenomenon resulting from coexpressing a toxic polyglutamine tract and a Drosophila gene, Dikar, with the GMR-Gal4/UAS system [22]. The synthetic lethality occurred when the simultaneous overexpression of two gene products, Dikar and an expanded polyglutamine tract, led to organismal death, whereas expressing either of them individually did not affect their viability.…”