Fig. 2.

Canonical upstream Hippo pathway components concentrate apically in columnar cells and are diluted in stretch cells to control Hippo kinase dimerisation and signalling. (A-E) The upstream Hippo pathway components, β-Heavy Spec (A), Crb (B), Kib (C), Ex (D) and Mer (E) strongly label the apical membrane domain of columnar follicle cells but become less concentrated in stretch cells. (F) Schematic diagram showing dilution of Kib, Ex and Mer proteins upon stretching of the apical domain. Green represents the apical domain. Purple/orange represents the apical-junctional ring of Crb-Ex and Mer-Kib complexes. Blue represents Yki localisation. (G-I) Measurement of Hippo kinase dimerisation with a split-Venus reporter reveals strong apical membrane signal in columnar cells and weak membrane signal in stretch cells. Both columnar and stretch cells have some cytoplasmic background Venus signal. G is a cross-section. H is a surface view. I contains magnified views of G and H. (J-L) Yki reporter gene expression is inversely correlated with Hippo kinase activation at the plasma membrane (compare with G-I). J is a cross-section. K is a surface view. L contains magnified views of G and H. (M) Schematic diagram showing dilution of upstream Hippo pathway complexes, reduced Hpo-Wts phosphorylation, reduced Yki phosphorylation, and increased Yki nuclear localisation and transcriptional activation upon stretching of the apical membrane domain. Measurement of Hpo dimerisation via the split-Venus BiFC reporter is diagrammed. Arrows indicate stretch cells.