A Caenorhabditis elegans model of orotic aciduria reveals enlarged lysosome-related organelles in embryos lacking umps-1 function.
Gut granules are cell type-specific lysosome-related organelles found within the intestinal cells of Caenorhabditis elegans. To investigate the regulation of lysosome-related organelle size, we screened for C. elegans mutants with substantially enlarged gut granules, identifying alleles of the vacuolar-type H(+)-ATPase and uridine-5'-monophosphate synthase (UMPS)-1. UMPS-1 catalyzes the conversion of orotic acid to UMP; this comprises the two terminal steps in de novo pyrimidine biosynthesis. Mutations in the orthologous human gene UMPS result in the rare genetic disease orotic aciduria. The umps-1(-) mutation promoted the enlargement of gut granules to 250 times their normal size, whereas other endolysosomal organelles were not similarly affected. UMPS-1::green fluorescent protein was expressed in embryonic and adult intestinal cells, where it was cytoplasmically localized and not obviously associated with gut granules. Whereas the umps-1(-) mutant is viable, combination of umps-1(-) with mutations disrupting gut granule biogenesis resulted in synthetic lethality. The effects of mutations in pyr-1, which encodes the enzyme catalyzing the first three steps of de novo pyrimidine biosynthesis, did not phenotypically resemble those of umps-1(-); instead, the synthetic lethality and enlargement of gut granules exhibited by the umps-1(-) mutant was suppressed by pyr-1(-). In a search for factors that mediate the enlargement of gut granules in the umps-1(-) mutant, we identified WHT-2, an ABCG transporter previously implicated in gut granule function. Our data suggest that umps-1(-) leads to enlargement of gut granules through a build-up of orotic acid. WHT-2 possibly facilitates the increase in gut granule size of the umps-1(-) mutant by transporting orotic acid into the gut granule and promoting osmotically induced swelling of the compartment.
Department of Biology, Lewis & Clark College, Portland, OR, USA.
Steven
S
Levitte
Rebecca
R
Salesky
Brian
B
King
Sage
S
Coe Smith
Micah
M
Depper
Madeline
M
Cole
Greg J
GJ
Hermann
D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000196:embryology / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D055786:Gene Knockout Techniques; D006801:Humans; D007814:Larva; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D009962:Orotate Phosphoribosyltransferase / Q000235:genetics* / Q000378:metabolism*; D009963:Orotic Acid / Q000378:metabolism*; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000235:genetics* / Q000378:metabolism*; D010316:Particle Size; D010641:Phenotype
D009097:Multienzyme Complexes; D009963:Orotic Acid; C027157:uridine 5'-monophosphate synthase; D009962:Orotate Phosphoribosyltransferase; D009964:Orotidine-5'-Phosphate Decarboxylase