A Drosophila Model of Neuronal Ceroid Lipofuscinosis CLN4 Reveals a Hypermorphic Gain of Function Mechanism

Elife. 2019 Oct 30;8:e46607. doi: 10.7554/eLife.46607.

Abstract

The autosomal dominant neuronal ceroid lipofuscinoses (NCL) CLN4 is caused by mutations in the synaptic vesicle (SV) protein CSPα. We developed animal models of CLN4 by expressing CLN4 mutant human CSPα (hCSPα) in Drosophila neurons. Similar to patients, CLN4 mutations induced excessive oligomerization of hCSPα and premature lethality in a dose-dependent manner. Instead of being localized to SVs, most CLN4 mutant hCSPα accumulated abnormally, and co-localized with ubiquitinated proteins and the prelysosomal markers HRS and LAMP1. Ultrastructural examination revealed frequent abnormal membrane structures in axons and neuronal somata. The lethality, oligomerization and prelysosomal accumulation induced by CLN4 mutations was attenuated by reducing endogenous wild type (WT) dCSP levels and enhanced by increasing WT levels. Furthermore, reducing the gene dosage of Hsc70 also attenuated CLN4 phenotypes. Taken together, we suggest that CLN4 alleles resemble dominant hypermorphic gain of function mutations that drive excessive oligomerization and impair membrane trafficking.

Keywords: D. melanogaster; cysteine-string protein; lysosome; neuronal ceroid lipofuscinosis; neuroscience.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Disease Models, Animal
  • Drosophila melanogaster / genetics*
  • Drosophila melanogaster / metabolism
  • Gain of Function Mutation*
  • HSP40 Heat-Shock Proteins / genetics
  • HSP40 Heat-Shock Proteins / metabolism
  • Humans
  • Lysosomal-Associated Membrane Protein 1 / genetics
  • Lysosomal-Associated Membrane Protein 1 / metabolism
  • Lysosomes / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Microscopy, Electron, Transmission
  • Neuronal Ceroid-Lipofuscinoses / genetics*
  • Neuronal Ceroid-Lipofuscinoses / metabolism
  • Neurons / metabolism*
  • Neurons / ultrastructure
  • Synaptic Vesicles / metabolism
  • Ubiquitinated Proteins / genetics
  • Ubiquitinated Proteins / metabolism

Substances

  • HSP40 Heat-Shock Proteins
  • Lysosomal-Associated Membrane Protein 1
  • Membrane Proteins
  • Ubiquitinated Proteins
  • cysteine string protein