Academic journal article Genetics

Genetic Modifiers of the Drosophila Blue Cheese Gene Link Defects in Lysosomal Transport with Decreased Life Span and Altered Ubiquitinated-Protein Profiles

Academic journal article Genetics

Genetic Modifiers of the Drosophila Blue Cheese Gene Link Defects in Lysosomal Transport with Decreased Life Span and Altered Ubiquitinated-Protein Profiles

Article excerpt

ABSTRACT

Defects in lysosomal trafficking pathways lead to decreased cell viability and are associated with progressive disorders in humans. Previously we have found that loss-of-function (LOF) mutations in the Drosophila gene blue cheese (bchs) lead to reduced adult life span, increased neuronal death, and widespread CNS degeneration that is associated with the formation of ubiquitinated-protein aggregates. To identify potential genes that participate in the bchs functional pathway, we conducted a genetic modifier screen based on alterations of an eye phenotype that arises from high-level overexpression of Bchs. We found that mutations in select autophagic and endocytic trafficking genes, defects in cytoskeletal and motor proteins, as well as mutations in the SUMO and ubiquitin signaling pathways behave as modifiers of the Bchs gain-of-function (GOF) eye phenotype. Individual mutant alleles that produced viable adults were further examined for bchs-like phenotypes. Mutations in several lysosomal trafficking genes resulted in significantly decreased adult life spans and several mutants showed changes in ubiquitinated protein profiles as young adults. This work represents a novel approach to examine the role that lysosomal transport and function have on adult viability. The genes characterized in this study have direct human homologs, suggesting that similar defects in lysosomal transport may play a role in human health and age-related processes.

LYSOSOMES are critical organelles for the turnover or degradation of a wide variety of cellular constituents (Dell'Angelica et al. 2000). A complex series of targeting and import pathways direct the flow of material to the lysosome and defects in these pathways are associated with many progressive conditions including lysosomal storage disorders, reduced viability, and neuraldegeneration(Cataldoet al.1996;Dell'Angelica et al.2000;BrunkandTerman2002;Cuervo2004).There are three main vesicle-based pathways for transport of material to the lysosome: transport from the trans-Golgi network (TGN), the endocytotic pathway, and macroautophagy (here after called autophagy) (Shih et al. 2002; Klionsky et al. 2003; Raiborg et al. 2003; Luzio et al. 2005). Autophagy involves the sequestration of cytoplasmic material and entire organelles into doublemembrane vesicles called autophagosomes, which are transported along microtubules for fusion with lysosomes, generating autolysosomes where the sequestered material is degraded(Klionsky andEmr2000). Groundbreaking genetic studies in yeast have allowed the identification and characterization of nearly 30 conserved autophagy (atg) genes (Klionsky et al. 2003). Inactivation of key components within the pathway has revealed that autophagy primarily functions as an adaptive response to starvation or cellular stress by recycling nonessential cellular components for nutrition or by clearing old or damaged cytoplasmic material and organelles (Scott et al. 2004; Komatsu et al. 2005). Recent genetic studies in mice have shown that ablation of the atg5 and atg7 genes in the CNS leads to progressive neurological defects, the formation of ubiquitinated inclusion bodies or protein aggregates, and neuronal cell death (Hara et al. 2006; Komatsu et al. 2006).

Previously we have shown that mutations in the Drosophila blue cheese (bchs) gene result in a reduced adult life span and age-related neuronal degeneration. These defects include neural atrophy and cell death, preceded by the accumulation of ubiquitin-conjugated protein aggregates throughout the adult CNS (Finley et al. 2003). Consistent with these findings is the recent characterization of Alfy (autophagy-linked FYVE protein) the conserved human bchs homolog (Figure 1a) (Simonsen et al. 2004). Under starvation conditions or following proteasomeinhibitor treatmentAlfy relocalizes from the nuclear membrane to cytoplasmic structures containing ubiquitin and early autophagic markers (Simonsen et al. …

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