“…For example, Drosophila simple columnar epithelia such as imaginal discs rely primarily on apical Crb-Mer/Ex-Kibra-Sav signalling to retain Yki in the cytoplasm and restrict tissue growth (Baumgartner et al, 2010;Chen et al, 2010;Genevet et al, 2010;Hamaratoglu et al, 2006;Ling et al, 2010;Yu et al, 2010). By contrast, Drosophila stratified columnar epithelia such as the intestine require integrins, Src, EGFR and Yki to promote proliferation of basal layer stem/progenitor cells, suggesting that the regulatory connection between them described here is also conserved (Cordero et al, 2014;Jiang et al, 2011;Kohlmaier et al, 2015;Lin et al, 2013;Shaw et al, 2010;Staley and Irvine, 2010;Xu et al, 2011). Furthermore, ectopic activation of Src, EGFR, PI3K or Yki in simple columnar imaginal discs is sufficient to induce overproliferation of cells, whereas loss of PI3K or Yki strongly impairs imaginal disc tumour formation (Doggett et al, 2011;Enomoto and Igaki, 2013;Fernandez et al, 2014;Herranz et al, 2012Herranz et al, , 2014Strassburger et al, 2012;Willecke et al, 2011).…”