Figure 4.

Ft associates with and is palmitoylated by App. (A) Coimmunoprecipitation between App and Ft^ΔECD in S2 cells. (B) App promotes palmitoylation of Ft in S2 cells. Mutation of the App DHHC motif (App^DHHS or App^DAHC) blocks this effect. Palm, palmitoylation. (C and D) Ft is palmitoylated by App in imaginal disc epithelia. Bands shown represent the 110-kD C-terminal fragment of Ft, which includes the ICD, treated with phosphatase. Immunoprecipitated Ft is palmitoylated, and coexpression of App promotes increased palmitoylation (C). Palmitoylation of 110-kD Ft is reduced in app^12-3 mutant imaginal discs (D). (E) The cysteine residues and functional domains in Ft-ICD (adapted from Matakatsu and Blair, 2012; Pan et al., 2013). The regions conserved between Ft and its human orthologue FAT atypical Cadherin 4 are shown in pink, and known functional domains are shown underneath. Conserved cysteine residues at 4,623, 4,938, and 4,987 are indicated. EGF, EGF-like domain; LG, Laminin G domain; TM, transmembrane domain. (F) Mapping of Ft palmitoylation sites using S2 cells. Mutation of Cys⁴⁶²³ (Ft^{ΔECD-4623C/S}) does not appear to affect Ft palmitoylation. Mutation of either Cys⁴⁹³⁸ (Ft^{ΔECD-4938C/S}) or Cys⁴⁹⁸⁷ (Ft^{ΔECD-4987C/S}) moderately decreases palmitoylation, whereas mutation of both together (Ft^ΔECD-2C/S) more severely affects palmitoylation (F). (G–K) Mutation of palmitoylated Cys residues in Ft results in decreased wing size. Representative wings from wild-type (G), ft^4938C/S (H), ft^4987C/S (I), and ft^2C/S (J) adults. Mutation of Cys⁴⁹³⁸, Cys⁴⁹⁸⁷, or both together leads to undergrowth (K), consistent with activation of Ft. Error bars are mean ± SEM. ***, P < 0.001 (two-tailed unpaired Student’s t test between wild type and each genotype). Bar, 100 µm.