The Caenorhabditis elegans mucolipin-like gene cup-5 is essential for viability and regulates lysosomes in multiple cell types

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Abstract
The misregulation of programmed cell death, or apoptosis, contributes to the pathogenesis of many diseases. We used Nomarski microscopy to screen for mutants containing refractile cell corpses in a C. elegans strain in which all programmed cell death is blocked and such corpses are absent. We isolated a mutant strain that accumulates refractile bodies resembling irregular cell corpses. We rescued this mutant phenotype with the C. elegans mucolipidosis type IV (ML-IV) homolog, the recently identified cup-5 (coelomocyte-uptake defective) gene. ML-IV is a human autosomal recessive lysosomal storage disease characterized by psychomotor retardation and ophthalmological abnormalities. Our null mutations in cup-5 cause maternal-effect lethality. In addition, cup-5 mutants contain excess lysosomes in many and possibly all cell types and contain lamellar structures similar to those observed in ML-IV cell lines. The human ML-IV gene is capable of rescuing both the maternal-effect lethality and the lysosome-accumulation abnormality of cup-5 mutants. cup-5 mutants seem to contain excess apoptotic cells as detected by staining with terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling. We suggest that the increased apoptosis seen in cup-5 mutants is a secondary consequence of the lysosomal defect, and that abnormalities in apoptosis may be associated with human lysosomal storage disorders.