Dynein light chain 1 is required for autophagy, protein clearance, and cell death inDrosophila

Abstract

Autophagy is a catabolic pathway that is important for turnover of long-lived proteins and organelles, and has been implicated in cell survival, tumor progression, protection from infection, neurodegeneration, and cell death. Autophagy and caspases are required for type II autophagic cell death of Drosophila larval salivary glands during development, but the mechanisms that regulate these degradation pathways are not understood. We conducted a forward genetic screen for genes that are required for salivary gland cell death, and here we describe the identification of Drosophila dynein light chain 1 (ddlc1) as a gene that is required for type II cell death. Autophagy is attenuated in ddlc1 mutants, but caspases are active in these cells. ddlc1 mutant salivary glands develop large fibrillar protein inclusions that stain positive for amyloid-specific dyes and ubiquitin. Ectopic expression of Atg1 is sufficient to induce autophagy, clear protein inclusions, and rescue degradation of ddlc1 mutant salivary glands. Furthermore, ddlc1 mutant larvae have decreased motility, and mutations in ddlc1 enhance the impairment of motility that is observed in a Drosophila model of neurodegenerative disease. Significantly, this decrease in larval motility is associated with decreased clearance of protein with polyglutamine expansion, the accumulation of p62 in neurons and muscles, and fewer synaptic boutons. These results indicate that DDLC1 is required for protein clearance by autophagy that is associated with autophagic cell death and neurodegeneration.macroautophagy | protein degradation | neurodegeneration M acroautophagy (autophagy) is a conserved catabolic pathway (1). Autophagy involves the formation of autophagosomes around cytoplasmic components, and fusion with lysosomes enables degradation of autophagosome cargo. Studies of yeast identified Atg genes that are required for autophagy during starvation (2-4). Autophagy is also activated during starvation in animals (5), but the complexity of higher animals, and the association of autophagy with diseases and cell death, raises questions about how autophagy is regulated and cargo is recruited and delivered to lysosomes in multicellular organisms.The role of autophagy in programmed cell death has been a subject of debate (6). Autophagy has a well established role in cell survival, and decreased Atg gene function can promote cell death (7). There is also evidence that autophagy plays a protective role against neurodegeneration in the setting of disease (8, 9), as well as under basal conditions (10, 11). Autophagosomes have been associated with dying cells during development (12, 13), and recent studies indicate that autophagy can promote the degradation and clearance of cells during cell death (14-17). This apparent paradoxical role of autophagy in both cell survival and death raises questions about how autophagy is regulated and influences different cell fates.Drosophila larval salivary glands possess type II cell death morphology during development, and contain numerous autop...

Autophagy in synaptic development, function, and pathology

“…Batlevi et al also reported a decreased number of synaptic boutons in dynein light chain 1 (ddlc1) mutant Drosophila that exhibited attenuated autophagic activity and reduced protein clearance [23] .…”

Human Disease Models inDrosophila melanogasterand the Role of the Fly in Therapeutic Drug Discovery

“…Polyglutamine diseases demonstrate several characteristic features in patients, such as nuclear inclusions containing the mutant protein, repeat length inversely correlated with age of onset, and age-dependent motor neuron degeneration and impairment. There are several D. melanogaster models of triplet repeat expansion diseases, including fragile X mental retardation with overexpression of the FMR1 gene with various CAG repeat lengths, HD using expression of truncated wild-type and mutant forms of huntingtin/htt , SCA 3 or MachadoJoseph disease expressing truncated ataxin 3 using different glutamine repeat lengths, and SBMA by expressing the human androgen receptor gene with different polyglutamine repeat lengths (Pandey et al, 2007a;Batlevi et al, 2010). All of these models demonstrated that increased poly-Gln expansion led to increased severity of degeneration, age-dependent degeneration, and repeat length-dependent protein aggregation (La Spada and Taylor, 2010).…”

Coordination of autophagosome–lysosome fusion and transport by a Klp98A–Rab14 complex in Drosophila

“…Klp98A promotes autophagosome-lysosome fusion, autophagic vesicle acidification and cargo degradation Previous studies have shown that microtubule-and dyneindependent transport of autophagosomes and lysosomes affects not only their intracellular location but also their fusion and activity (Batlevi et al, 2010;Jahreiss et al, 2008;Köchl et al, 2006;Maday et al, 2012), although similar requirements for kinesin-related proteins have not yet been reported. We therefore characterized the functionality of the redistributed autophagic vesicles resulting from Klp98A depletion.…”