Figure 4

Xrp1 regulates its own expression, the expression of pro-apoptotic genes and of genes previously linked to cell competition. ChIP-seq on Xrp1 OE wing discs reveals targets of Xrp1, including rDNA, Xrp1 itself, pro-apoptotic genes such as hid and rpr and several other genes that have been linked to either cell competition or cell proliferation (A). Using a transcriptional reporter for Xrp1 and via the overexpression of Xrp1 in the posterior compartment (en-Gal4), immunostaining reveals a positive feedback loop by which Xrp1 regulates its own transcription. Xrp1 (B-B’). The observation is confirmed by qPCR, Xrp1 is overexpressed in the wing disc 24 hours before analysis. We used primers that recognize all forms of Xrp1 including the overexpressed isoform and confirmed that the Xrp1 overexpression construct is functional (Xrp1 all). With primers that detect only the endogenous forms of Xrp1 we observe Xrp1-dependent induction of Xrp1 expression (Xrp1 vlong, Xrp1 3′UTR) (C). A representative example showing upregulation of the Dif protein upon overexpression of Xrp1 in the posterior compartment (D-D’). Effects on putative Xrp1 target genes are confirmed via qPCRs. The pro-apoptotic gene rpr is upregulated in response to Xrp1 OE in wing discs. Xrp1 OE is induced 24 hours before analysis (E). Other putative target genes are also upregulated under the same conditions, respectively Dif, puc, Upd3, Nedd4 and rad50 (F). t-test was applied. *P < 0.05; **P < 0.01; ***P < 0.001.