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Defective pigment granule biogenesis and aberrant behavior caused by mutations in the Drosophila AP-3beta adaptin
D Kretzschmar1, B Poeck, H Roth
1Lehrstuhl für Genetik, Theodor-Boveri-Institut, Biozentrum, Universität Würzburg, D 97074 Würzburg, Germany.
Abstract:
Lysosomal protein trafficking is a fundamental process conserved from yeast to humans. This conservation extends to lysosome-like organelles such as mammalian melanosomes and insect eye pigment granules. Recently, eye and coat color mutations in mouse (mocha and pearl) and Drosophila (garnet and carmine) were shown to affect subunits of the heterotetrameric adaptor protein complex AP-3 involved in vesicle trafficking. Here we demonstrate that the Drosophila eye color mutant ruby is defective in the AP-3beta subunit gene. ruby expression was found in retinal pigment and photoreceptor cells and in the developing central nervous system. ruby mutations lead to a decreased number and altered size of pigment granules in various cell types in and adjacent to the retina. Humans with lesions in the related AP-3betaA gene suffer from Hermansky-Pudlak syndrome, which is caused by defects in a number of lysosome-related organelles. Hermansky-Pudlak patients have a reduced skin pigmentation and suffer from internal bleeding, pulmonary fibrosis, and visual system malfunction. The Drosophila AP-3beta adaptin also appears to be involved in processes other than eye pigment granule biogenesis because all ruby allele combinations tested exhibited defective behavior in a visual fixation paradigm.
Insights
The Drosophila ruby mutant reveals a defect in AP-3beta, a protein complex crucial for lysosomal trafficking. This finding links eye color mutations to fundamental cellular processes and human diseases like Hermansky-Pudlak syndrome.
Area of Science:
- Cell Biology
- Genetics
- Developmental Biology
Background:
- Lysosomal protein trafficking is vital and conserved across species, impacting organelles like melanosomes.
- Mutations in adaptor protein complex AP-3 subunits are linked to eye and coat color defects in mice and Drosophila.
- The AP-3 complex mediates vesicle trafficking, essential for organelle biogenesis and function.
Purpose of the Study:
- To investigate the genetic basis of the Drosophila eye color mutant ruby.
- To determine the role of the AP-3 complex in pigment granule formation and other cellular processes in Drosophila.
- To establish a model for understanding human disorders related to lysosomal trafficking defects.
Main Methods:
- Genetic analysis of the Drosophila ruby mutant.
- Expression pattern analysis of the ruby gene in various tissues.
- Phenotypic characterization of pigment granules in ruby mutants.
- Behavioral assays to assess visual function in ruby mutants.
Main Results:
- The Drosophila ruby mutant exhibits a defect in the AP-3beta subunit gene.
- ruby expression is detected in retinal pigment, photoreceptor cells, and the central nervous system.
- Mutations result in fewer and larger pigment granules in retinal and adjacent cells.
- ruby mutants display impaired visual fixation, indicating roles beyond pigment granule biogenesis.
Conclusions:
- The AP-3beta subunit is essential for proper pigment granule biogenesis in Drosophila.
- The Drosophila AP-3beta adaptin plays a role in visual system function.
- This study provides insights into the conserved function of AP-3 in lysosome-related organelle biogenesis and its relevance to human diseases.