C. elegans gut granules represent a model system for studying lysosome biogenesis during metazoan development. Gut granules are exclusively localized to intestinal cells and they contain easily visualized birefringent and autofluorescent material. These characteristics have led to their extensive use as a marker for intestinal cell fate. We have identified a collection of glo mutants that properly specify gut cells, however they lack gut granules and/or mislocalize birefringent material into the embryonic intestinal lumen. One phenotypic class identifies AP-3 complex mutants, including
apt-6 and
apt-7. The AP-3 adaptin complex is involved in trafficking cargo from the Golgi to lysosomes. AP-3 complex mutants are phenotypically distinct from
glo-1,
glo-3, and
glo-4 mutants. In order to investigate the functional interactions between these two phenotypic classes,
glo-1;
apt-6,
glo-3;
apt-6, and
glo-4;
apt-6 mutants were analyzed and found to have the
glo-1,-3,-4 phenotype. These results suggest that GLO-1, GLO-3, and GLO-4 function in a trafficking step distinct from AP-3.
glo-1 encodes a protein homologous to Drosophila Rab-RP1 and mammalian Rab38, two Rab proteins that function the formation of specialized lysosomes.
glo-4 encodes a predicted exchange factor for GLO-1 that is homologous to the Drosophila Rab-RP1 exchange factor, Claret. Currently, the function of these evolutionarily conserved Rab proteins in lysosome biogenesis is unknown. The phenotype and genetic interactions exhibited by
glo-3 suggest that it might function with
glo-1 and
glo-4 in gut granule biogenesis. We have isolated three recessive alleles of
glo-3 and genetic mapping has located
glo-3 to a 1 m.u. interval on LGX. We are currently using snip-SNP mapping to narrow this interval and we will present results of experiments aimed at identifying the
glo-3 gene.