Common and Distinct Genetic Properties of ESCRT-II Components in Drosophila

Abstract

BackgroundGenetic studies in yeast have identified class E vps genes that form the ESCRT complexes required for protein sorting at the early endosome. In Drosophila, mutations of the ESCRT-II component vps25 cause endosomal defects leading to accumulation of Notch protein and increased Notch pathway activity. These endosomal and signaling defects are thought to account for several phenotypes. Depending on the developmental context, two different types of overgrowth can be detected. Tissue predominantly mutant for vps25 displays neoplastic tumor characteristics. In contrast, vps25 mutant clones in a wild-type background trigger hyperplastic overgrowth in a non-autonomous manner. In addition, vps25 mutant clones also promote apoptotic resistance in a non-autonomous manner.Principal FindingsHere, we genetically characterize the remaining ESCRT-II components vps22 and vps36. Like vps25, mutants of vps22 and vps36 display endosomal defects, accumulate Notch protein and – when the tissue is predominantly mutant – show neoplastic tumor characteristics. However, despite these common phenotypes, they have distinct non-autonomous phenotypes. While vps22 mutations cause strong non-autonomous overgrowth, they do not affect apoptotic resistance. In contrast, vps36 mutations increase apoptotic resistance, but have little effect on non-autonomous proliferation. Further characterization reveals that although all ESCRT-II mutants accumulate Notch protein, only vps22 and vps25 mutations trigger Notch activity.Conclusions/SignificanceThe ESCRT-II components vps22, vps25 and vps36 display common and distinct genetic properties. Our data redefine the role of Notch for hyperplastic and neoplastic overgrowth in these mutants. While Notch is required for hyperplastic growth, it appears to be dispensable for neoplastic transformation.

Loss- and gain-of-function analyses of <i>vacuolar protein sorting 2</i> in Notch signaling of <i>Drosophila melanogaster</i>

“…This result is consistent with previous reports in which cells homozygous for mutant alleles of genes encoding other ESCRT components also failed to form large clones (Moberg et al, 2005;Thompson et al, 2005;Vaccari and Bilder, 2005;Herz et al, 2006). This phenomenon was shown to be due to cell competition, because under conditions in which apoptosis in these cells was suppressed, the clones over-proliferated (Thompson et al, 2005;Herz et al, 2006Herz et al, , 2009. Thus, it is likely that the small clones homozygous for vps2 2 resulted from their selective removal by cell competition in our experiments.…”

“…Thus, it is likely that the small clones homozygous for vps2 2 resulted from their selective removal by cell competition in our experiments. An over-proliferation phenotype was reported in mutants of ESCRT-I-, ESCRT-II-and ESCRET-III-encoding genes, under conditions in which the apoptosis associated with cell competition was suppressed in the homozygous mutant cells (Thompson et al, 2005;Herz et al, 2006Herz et al, , 2009Vaccari et al, 2009). The previously isolated vps2 allele also induces over-proliferation in the eye imaginal discs under such conditions (Vaccari et al, 2009).…”

Atg6 is required for multiple vesicle trafficking pathways and hematopoiesis in Drosophila

“…This conclusion is supported by the similarity between Atg6 and ESCRT II and III endocytic tracer phenotypes in the fat body. Therefore, it is possible that loss of Atg6 is similar to ESCRT mutants in flies, and that the Vps34 complex 1327 RESEARCH ARTICLE Atg6 function in Drosophila regulates receptor downregulation because of similar defects in endocytosis (Herz et al, 2006;Herz et al, 2009;Thompson et al, 2005;Vaccari and Bilder, 2005;Vaccari et al, 2009). However, the lack of an obvious Atg6 mutant eye over-growth phenotype suggests that Atg6 mutants are different from ESCRT pathway mutants.…”

“…Loss of ESCRT components in the developing Drosophila eye impairs MVB formation and leads to defects in receptor degradation that cause tissue overgrowth (Fig. 3A,D) (Herz et al, 2006;Herz et al, 2009;Thompson et al, 2005;Vaccari and Bilder, 2005;Vaccari et al, 2009). By contrast, eye imaginal disc tissue isolated from homozygous Atg6 1 animals at the same third larval instar stage is normal in size (Fig.…”

Genetic identification of intracellular trafficking regulators involved in notch dependent binary cell fate acquisition following asymmetric cell division

“…Accumulation at the interface and/or endosomes can result from a blockade in endosome maturation when ESCRT function is impaired and it has already been described that accumulation of Notch in endocytic compartments can result in an ectopic ligand-independent activation of Notch (Herz et al, 2009;Moberg et al, 2005;Thompson et al, 2005;Vaccari and Bilder, 2005;Vaccari et al, 2009). Additionally, ESCRT complexes are involved in various cellular mechanisms: cargo engagement and/or deubiquitylation, maturation of multi vesicular bodies, vesicle budding and/or cytokinesis (for a review, see Henne et al, 2011).…”