alan shepard, A modifier of polyglutamine toxicity in Drosophila melanogaster

Neurodegenerative diseases, such as Machado-Joseph Disease (MJD), are associated with a polyglutamine expansion within a host protein. Pathological development is well studied, but not completely understood. Disease is thought to be related to protein aggregate formation in the cytoplasm, which localize to the nucleus as nuclear inclusions (NIs). Others have developed a polyglutamine disease model in Drosophila eye tissue, which expresses a disease-related gene, MJDtr-Q78. The gene encodes for a protein, Q78, which leads to neuronal toxicity in eye tissues and is easily identifiable. A potential modifier, which enhances this phenotype, was found in the 64C region of Chromosome 3. Alleles that contained transposable element (TE) induced mutations within a gene in this region, alan shepard (shep), were found to enhance the phenotype. Genetic and molecular verification show that the enhancement is directly linked to the TE, which suggests shep influences the toxicity caused by the toxic protein. Genomic analyses suggest shep encodes for an RNA binding protein. A histo-immunochemical stain reveals shep does not affect aggregate or NI formation, indicating an indirect relationship with polyglutamine diseases. shep does not modify a second polyglutamine-associated disease background, 97QP. This suggests that shep influences independent of the polyglutamine expansion tract. An investigation of the biological significance of shep reveals that the gene is required for development past pupation. Together these data support the current model, which is, although polyglutamine diseases are related to an expansion of the polyglutamine tract, their disease development can be independent of each other.

Synthetic Lethality Induced by a Strong Drosophila Enhancer of Expanded Polyglutamine Tract

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 Drosophilagenes 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 Drosophilagene 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

Coincidence of P-Insertion Sites and Breakpoints of Deletions Induced by Activating P Elements in Drosophila

We isolated a set of seven deletions in the 67B region by activating a nearby P-element insertion. The structures of the deletions were characterized by cloning and sequencing. The results showed that the P-induced deletions occurred nonrandomly in the genomic sites. One breakpoint of the deletions was located precisely at the end of the starting element, i.e., at the end of the inverted terminal repeats. The other breakpoint was nearby the retained starting element and coincided with preferential P-element insertion sites that harbor transcription initiation activities. It is known that P elements induce male recombination near the starting elements, giving rise to deletions with one breakpoint precisely located at an inverted terminal repeat of the retained starting element. Database analyses further revealed that deletions generated in P-induced male recombination also contained the other breakpoint in genomic regions that coincided with preferential P-insertion sites. The results suggest that nonrandom distribution of the deletion breakpoints is characteristic of the mechanism by which P elements induce deletions near the starting elements