ESCRT-deficient cells also activate Notch signalling, which triggers the release of a cytokine thus activating proliferation in adjacent, normal cells. In this paper, we focus on the cell autonomous effects caused by ESCRT deficiency. Even though it is established that the ESCRTs control tissue organization, the mechanisms that mediate this activity remain unclear. Here we explore the effects of reducing the activity of Drosophila Vps4, the most downstream component of the ESCRT machinery. In the main, dVps4 activity was knocked down with a dominant negative construct carrying a point mutation in the catalytic site. Supportive evidence was also obtained with a small genomic deletion and an RNAi hairpin construct. We find that several cell-autonomous effects observed when ESCRT function is disrupted are mediated by c-Jun Nterminal kinase, a member of the mitogen-activated protein kinase family, which has extensively been implicated in programmed cell death and is misregulated in many types of mammalian cancers. While reduction in either dVps4 activity or JNK signalling does not cause overgrowth, double deficiency leads to the formation of neoplastic tumours. Expression of this transgene in wing imaginal discs caused accumulation of endocytic cargo, polarity disruption and cell death. These are characteristics of the loss of function phenotype and it is therefore Choline Chloride likely that overexpressed wild type protein has a dominant negative effect on ESCRT activity. Since the dvps4D7b mutant clones are so short lived and because of the possibility that the flanking genes might be affected by the deletion, we turned to RNAi-mediated knock-down and a dominant negative form of dVps4, dVps4-DN as means of reducing dVps4 activity. Since both the RNAi and the DN constructs can be expressed under Gal4 control and since these constructs are likely to create a hypomorphic situation, large patches of deficient tissue can be generated thus overcoming the Deferiprone problem of growth from a single mutant cell. As a first step, heat-shock-inducible Gal4 was used to activate the UAS-dVps4-DN transgene ubiquitously, and egg chamber phenotypes were scored. As can be seen in Fig. 2B, this caused the accumulation of the endosome marker Hrs and conjugated ubiquitin on large structures within expressing cells. In addition we used phalloidin staining to visualize F-actin and found that the cytoskeleton was disrupted with tangles of abnormal accumulation.