Genetic analysis of the Drosophila ESCRT-III complex protein, VPS24, reveals requirements in lysosome homeostasis and autophagy

Open Access
Author:
Florian, Jonathan
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Fumiko Kawasaki, Thesis Supervisor
  • Richard W Ordway, Honors Advisor
Keywords:
  • Drosophila melanogaster
  • neurodegeneration
  • VPS24
  • ESCRT
  • autophagy
  • lysosome homeostasis
Abstract:
The ESCRT (Endosomal Sorting Complexes Required for Transport) pathway is evolutionarily conserved across all eukaryotes and plays key roles in a variety of membrane remodeling processes. A new Drosophila mutant recovered in our forward genetic screens mapped to the vps24 gene encoding a subunit of the ESCRT-III complex. Molecular characterization of the mutation predicted a complete loss of VPS24 function. However, the mutant flies develop to adulthood and thus the consequences of removing VPS24 may be studied in a viable multicellular organism. Flies lacking VPS24 function exhibit locomotor deficits and reduced lifespans. Interestingly, these phenotypes were largely rescued by neuronal expression of wild-type VPS24. Further examination revealed that both neuronal and muscle cells exhibit marked expansion of a ubiquitin-positive lysosomal compartment as well as accumulation of autophagic intermediates. Ultrastructural analysis of the vps24[1] mutant confirmed these observations and revealed that a major component of the expanded neuronal lysosome compartment exhibited a striking tubular network morphology. The results reported indicate that loss of VPS24 function disrupts lysosome homeostasis, as well as autophagy, and suggest a novel role for ESCRT function in lysosome biogenesis through tubular intermediates. To further define the role of VPS24 in this process, we generated transgenic lines expressing VPS24 with a mutated MIM domain expected to disrupt its ability to associate with intermediates in the pathway. Analysis of these lines may further elucidate the role of the ESCRT pathway in lysophagy and lysosome reformation. These studies provide new insight into the in vivo functions of the ESCRT pathway in cellular homeostasis and their potential roles in neurodegenerative diseases characterized by defective ESCRT or lysosome function.