The role of atg18 in signal transduction pathways during Drosophila development

Abstract

8J16 and 9E6 are allelic mutations that disrupt Wnt/Wingless (Wg) or Hedgehog (Hh) signaling based upon their embryonic ‘lawn of denticles’ phenotype. Goals of this project were to identify the disrupted gene and determine its role in Drosophila developmental signaling. Complementation analysis revealed 8J16/9E6 are alleles of autophagy‐specific gene 18, atg18, which plays a role in autophagosome‐lysosome fusion. In yeast, atg18 negatively regulates endosome‐lysosome targeting. In Drosophila, endocytic machinery mutations that block lysosome targeting cause continuous signaling. Thus, atg18 mutants should show a buildup of lysosomes at the expense of endosomes and decrease signaling. To the contrary, Distalless, a long‐range Wg target, was enhanced in 8J16/9E6 mutant tissue in Drosophila wing discs. Analysis of 8J16/9E6 germline clone (glc) mutant embryos confirmed atg188J16, atg189E6, and atg18KG03090 are allelic. Immunofluorescent staining of glc embryos showed the segmentation defect is due to loss of Wg expression at embryonic stage 9. 8J16/9E6 glc embryos also display severe CNS defects not strictly the result of Wg loss and thus, are pleiotropic effects of these mutations. 8J16/9E6 are intronic point mutations not predicted to disrupt mRNA splicing and are temperature sensitive, yielding lethality at 25ºC, but are viable at 29ºC. Molecular explanations for this phenotype are explored. HHMI.