Planar cell polarity (PCP) is a second polarity axis orthogonal to the apicobasal axis in the plane of the epithelium. The molecular link between apicobasal polarity and PCP is largely unknown. During Drosophila eye development, differentiated photoreceptors form clusters that rotate independently of the surrounding interommatidial cells (ICs). Here, we demonstrate that both Echinoid (Ed), an adherens junction (AJ)-associated cell adhesion molecule (CAM), and Flamingo (Fmi), a PCP determinant, are endocytosed via a clathrin-mediated pathway in ICs. Interestingly, we found that Ed binds AP-2 adaptor and is required for the internalization of Fmi into ICs. Loss of ed led to increased amounts of Fmi on the cell membrane of non-rotating ICs and also to the misrotation of photoreceptor clusters. Importantly, overexpression of fmi in ICs alone was sufficient to cause misrotation of the adjacent photoreceptor clusters. Together, we propose that Ed, when internalized by AP-2, might co-endocytose with and thereby decrease Fmi levels on non-rotating ICs to permit correct rotation of ommatidial clusters. Thus, co-endocytosis of Ed and Fmi provides a link between apicobasal polarity and PCP.

Adler, P. N. (2002). Planar signaling and morphogenesis in Drosophila. Dev Cell 2, 525-35.
Adler, P. N., Charlton, J. and Liu, J. (1998). Mutations in the cadherin superfamily member gene dachsous cause a tissue polarity phenotype by altering frizzled signaling. Development 125, 959-68.
Ahmed, A., Chandra, S., Magarinos, M. and Vaessin, H. (2003). Echinoid mutants exhibit neurogenic phenotypes and show synergistic interactions with the Notch signaling pathway. Development 130, 6295-304.
Bai, J., Chiu, W., Wang, J., Tzeng, T., Perrimon, N. and Hsu, J. (2001). The cell adhesion molecule Echinoid defines a new pathway that antagonizes the Drosophila EGF receptor signaling pathway. Development 128, 591-601.
Bastock, R. and Strutt, D. (2007). The planar polarity pathway promotes coordinated cell migration during Drosophila oogenesis. Development 134, 3055-64.
Bilder, D., Li, M. and Perrimon, N. (2000). Cooperative regulation of cell polarity and growth by Drosophila tumor suppressors. Science 289, 113-6.
Bilder, D. and Perrimon, N. (2000). Localization of apical epithelial determinants by the basolateral PDZ protein Scribble. Nature 403, 676-80.
Bonifacino, J. S. and Lippincott-Schwartz, J. (2003). Coat proteins: shaping membrane transport. Nat Rev Mol Cell Biol 4, 409-14.
Carthew, R. W. (2007). Pattern formation in the Drosophila eye. Curr Opin Genet Dev 17, 309-13.
Chang, W. L., Liou, W., Pen, H. C., Chou, H. Y., Chang, Y. W., Li, W. H., Chiang, W. and Pai, L. M. (2008). The gradient of Gurken, a long-range morphogen, is directly regulated by Cbl-mediated endocytosis. Development 135, 1923-33.
Cooper, M. T. and Bray, S. J. (1999). Frizzled regulation of Notch signalling polarizes cell fate in the Drosophila eye. Nature 397, 526-30.
Daga, A., Karlovich, C. A., Dumstrei, K. and Banerjee, U. (1996). Patterning of cells in the Drosophila eye by Lozenge, which shares homologous domains with AML1. Genes Dev 10, 1194-205.
Das, G., Jenny, A., Klein, T. J., Eaton, S. and Mlodzik, M. (2004). Diego interacts with Prickle and Strabismus/Van Gogh to localize planar cell polarity complexes. Development 131, 4467-76.
Das, G., Reynolds-Kenneally, J. and Mlodzik, M. (2002). The atypical cadherin Flamingo links Frizzled and Notch signaling in planar polarity establishment in the Drosophila eye. Dev Cell 2, 655-66.
Dunn, K. W., McGraw, T. E. and Maxfield, F. R. (1989). Iterative fractionation of recycling receptors from lysosomally destined ligands in an early sorting endosome. J Cell Biol 109, 3303-14.
Entchev, E. V., Schwabedissen, A. and Gonzalez-Gaitan, M. (2000). Gradient formation of the TGF-beta homolog Dpp. Cell 103, 981-91.
Escudero, L. M., Wei, S. Y., Chiu, W. H., Modolell, J. and Hsu, J. C. (2003). Echinoid synergizes with the Notch signaling pathway in Drosophila mesothorax bristle patterning. Development 130, 6305-16.
Fanto, M. and Mlodzik, M. (1999). Asymmetric Notch activation specifies photoreceptors R3 and R4 and planar polarity in the Drosophila eye. Nature 397, 523-6.
Fetting, J. L., Spencer, S. A. and Wolff, T. (2009). The cell adhesion molecules Echinoid and Friend of Echinoid coordinate cell adhesion and cell signaling to regulate the fidelity of ommatidial rotation in the Drosophila eye. Development 136, 3323-33.
Fiehler, R. W. and Wolff, T. (2007). Drosophila Myosin II, Zipper, is essential for ommatidial rotation. Dev Biol 310, 348-62.
Fiehler, R. W. and Wolff, T. (2008). Nemo is required in a subset of photoreceptors to regulate the speed of ommatidial rotation. Dev Biol 313, 533-44.
Flores, G. V., Duan, H., Yan, H., Nagaraj, R., Fu, W., Zou, Y., Noll, M. and Banerjee, U. (2000). Combinatorial signaling in the specification of unique cell fates. Cell 103, 75-85.
Frankfort, B. J. and Mardon, G. (2002). R8 development in the Drosophila eye: a paradigm for neural selection and differentiation. Development 129, 1295-306.
Freeman, M. (1996). Reiterative use of the EGF receptor triggers differentiation of all cell types in the Drosophila eye. Cell 87, 651-60.
Friedlander, D. R., Mege, R. M., Cunningham, B. A. and Edelman, G. M. (1989). Cell sorting-out is modulated by both the specificity and amount of different cell adhesion molecules (CAMs) expressed on cell surfaces. Proc Natl Acad Sci U S A 86, 7043-7.
Gorvel, J. P., Chavrier, P., Zerial, M. and Gruenberg, J. (1991). rab5 controls early endosome fusion in vitro. Cell 64, 915-25.
Grant, B. D. and Donaldson, J. G. (2009). Pathways and mechanisms of endocytic recycling. Nat Rev Mol Cell Biol 10, 597-608.
Grawe, F., Wodarz, A., Lee, B., Knust, E. and Skaer, H. (1996). The Drosophila genes crumbs and stardust are involved in the biogenesis of adherens junctions. Development 122, 951-9.
Gruenberg, J. and Maxfield, F. R. (1995). Membrane transport in the endocytic pathway. Curr Opin Cell Biol 7, 552-63.
Guo, N., Hawkins, C. and Nathans, J. (2004). Frizzled6 controls hair patterning in mice. Proc Natl Acad Sci U S A 101, 9277-81.
Hacohen, N., Kramer, S., Sutherland, D., Hiromi, Y. and Krasnow, M. A. (1998). sprouty encodes a novel antagonist of FGF signaling that patterns apical branching of the Drosophila airways. Cell 92, 253-63.
Heberlein, U., Wolff, T. and Rubin, G. M. (1993). The TGF beta homolog dpp and the segment polarity gene hedgehog are required for propagation of a morphogenetic wave in the Drosophila retina. Cell 75, 913-26.
Higashijima, S., Kojima, T., Michiue, T., Ishimaru, S., Emori, Y. and Saigo, K. (1992). Dual Bar homeo box genes of Drosophila required in two photoreceptor cells, R1 and R6, and primary pigment cells for normal eye development. Genes Dev 6, 50-60.
Honing, S., Ricotta, D., Krauss, M., Spate, K., Spolaore, B., Motley, A., Robinson, M., Robinson, C., Haucke, V. and Owen, D. J. (2005). Phosphatidylinositol-(4,5)-bisphosphate regulates sorting signal recognition by the clathrin-associated adaptor complex AP2. Mol Cell 18, 519-31.
Inoue, T., Tanaka, T., Takeichi, M., Chisaka, O., Nakamura, S. and Osumi, N. (2001). Role of cadherins in maintaining the compartment boundary between the cortex and striatum during development. Development 128, 561-9.
Islam, R., Wei, S. Y., Chiu, W. H., Hortsch, M. and Hsu, J. C. (2003). Neuroglian activates Echinoid to antagonize the Drosophila EGF receptor signaling pathway. Development 130, 2051-9.
Ito, K., Awano, W., Suzuki, K., Hiromi, Y. and Yamamoto, D. (1997). The Drosophila mushroom body is a quadruple structure of clonal units each of which contains a virtually identical set of neurones and glial cells. Development 124, 761-71.
Jenny, A., Reynolds-Kenneally, J., Das, G., Burnett, M. and Mlodzik, M. (2005). Diego and Prickle regulate Frizzled planar cell polarity signalling by competing for Dishevelled binding. Nat Cell Biol 7, 691-7.
Johnson, K. and Wodarz, A. (2003). A genetic hierarchy controlling cell polarity. Nat Cell Biol 5, 12-4.
Kimura, H., Usui, T., Tsubouchi, A. and Uemura, T. (2006). Potential dual molecular interaction of the Drosophila 7-pass transmembrane cadherin Flamingo in dendritic morphogenesis. J Cell Sci 119, 1118-29.
Kirkham, M. and Parton, R. G. (2005). Clathrin-independent endocytosis: new insights into caveolae and non-caveolar lipid raft carriers. Biochim Biophys Acta 1745, 273-86.
Klein, T. J. and Mlodzik, M. (2005). Planar cell polarization: an emerging model points in the right direction. Annu Rev Cell Dev Biol 21, 155-76.
Laplante, C. and Nilson, L. A. Asymmetric distribution of Echinoid defines the epidermal leading edge during Drosophila dorsal closure. J Cell Biol 192, 335-48.
Laplante, C. and Nilson, L. A. (2006). Differential expression of the adhesion molecule Echinoid drives epithelial morphogenesis in Drosophila. Development 133, 3255-64.
Laplante, C. and Nilson, L. A. (2011). Asymmetric distribution of Echinoid defines the epidermal leading edge during Drosophila dorsal closure. J Cell Biol 192, 335-48.
Lin, H. P., Chen, H. M., Wei, S. Y., Chen, L. Y., Chang, L. H., Sun, Y. J., Huang, S. Y. and Hsu, J. C. (2007). Cell adhesion molecule Echinoid associates with unconventional myosin VI/Jaguar motor to regulate cell morphology during dorsal closure in Drosophila. Dev Biol 311, 423-33.
Littleton, J. T. and Bellen, H. J. (1994). Genetic and phenotypic analysis of thirteen essential genes in cytological interval 22F1-2; 23B1-2 reveals novel genes required for neural development in Drosophila. Genetics 138, 111-23.
Ma, C., Zhou, Y., Beachy, P. A. and Moses, K. (1993). The segment polarity gene hedgehog is required for progression of the morphogenetic furrow in the developing Drosophila eye. Cell 75, 927-38.
Mahoney, P. A., Weber, U., Onofrechuk, P., Biessmann, H., Bryant, P. J. and Goodman, C. S. (1991). The fat tumor suppressor gene in Drosophila encodes a novel member of the cadherin gene superfamily. Cell 67, 853-68.
Maldonado-Baez, L. and Wendland, B. (2006). Endocytic adaptors: recruiters, coordinators and regulators. Trends Cell Biol 16, 505-13.
Martin, A. C. and Wieschaus, E. F. Tensions divide. Nat Cell Biol 12, 5-7.
Mayor, S. and Pagano, R. E. (2007). Pathways of clathrin-independent endocytosis. Nat Rev Mol Cell Biol 8, 603-12.
Mellman, I. (1996). Endocytosis and molecular sorting. Annu Rev Cell Dev Biol 12, 575-625.
Miller, D. T. and Cagan, R. L. (1998). Local induction of patterning and programmed cell death in the developing Drosophila retina. Development 125, 2327-35.
Mirkovic, I. and Mlodzik, M. (2006). Cooperative activities of drosophila DE-cadherin and DN-cadherin regulate the cell motility process of ommatidial rotation. Development 133, 3283-93.
Miyoshi, J. and Takai, Y. (2007). Nectin and nectin-like molecules: biology and pathology. Am J Nephrol 27, 590-604.
Newsome, T. P., Asling, B. and Dickson, B. J. (2000). Analysis of Drosophila photoreceptor axon guidance in eye-specific mosaics. Development 127, 851-60.
Nose, A., Nagafuchi, A. and Takeichi, M. (1988). Expressed recombinant cadherins mediate cell sorting in model systems. Cell 54, 993-1001.
Oda, H. and Tsukita, S. (2001). Real-time imaging of cell-cell adherens junctions reveals that Drosophila mesoderm invagination begins with two phases of apical constriction of cells. J Cell Sci 114, 493-501.
Perez-Moreno, M., Jamora, C. and Fuchs, E. (2003). Sticky business: orchestrating cellular signals at adherens junctions. Cell 112, 535-48.
Pfeffer, S. (2003). Membrane domains in the secretory and endocytic pathways. Cell 112, 507-17.
Rawlins, E. L., Lovegrove, B. and Jarman, A. P. (2003a). Echinoid facilitates Notch pathway signalling during Drosophila neurogenesis through functional interaction with Delta. Development 130, 6475-84.
Rawlins, E. L., White, N. M. and Jarman, A. P. (2003b). Echinoid limits R8 photoreceptor specification by inhibiting inappropriate EGF receptor signalling within R8 equivalence groups. Development 130, 3715-24.
Sanson, B., White, P. and Vincent, J. P. (1996). Uncoupling cadherin-based adhesion from wingless signalling in Drosophila. Nature 383, 627-30.
Schock, F. and Perrimon, N. (2002). Molecular mechanisms of epithelial morphogenesis. Annu Rev Cell Dev Biol 18, 463-93.
Soldati, T. and Schliwa, M. (2006). Powering membrane traffic in endocytosis and recycling. Nat Rev Mol Cell Biol 7, 897-908.
Spencer, S. A. and Cagan, R. L. (2003). Echinoid is essential for regulation of Egfr signaling and R8 formation during Drosophila eye development. Development 130, 3725-33.
Steinberg, M. S. and Takeichi, M. (1994). Experimental specification of cell sorting, tissue spreading, and specific spatial patterning by quantitative differences in cadherin expression. Proc Natl Acad Sci U S A 91, 206-9.
Stowers, R. S. and Schwarz, T. L. (1999). A genetic method for generating Drosophila eyes composed exclusively of mitotic clones of a single genotype. Genetics 152, 1631-9.
Strutt, D., Johnson, R., Cooper, K. and Bray, S. (2002). Asymmetric localization of frizzled and the determination of notch-dependent cell fate in the Drosophila eye. Curr Biol 12, 813-24.
Strutt, H., Price, M. A. and Strutt, D. (2006). Planar polarity is positively regulated by casein kinase Iepsilon in Drosophila. Curr Biol 16, 1329-36.
Strutt, H. and Strutt, D. (1999). Polarity determination in the Drosophila eye. Curr Opin Genet Dev 9, 442-6.
Strutt, H. and Strutt, D. (2003). EGF signaling and ommatidial rotation in the Drosophila eye. Curr Biol 13, 1451-7.
Swan, L. E., Schmidt, M., Schwarz, T., Ponimaskin, E., Prange, U., Boeckers, T., Thomas, U. and Sigrist, S. J. (2006). Complex interaction of Drosophila GRIP PDZ domains and Echinoid during muscle morphogenesis. EMBO J 25, 3640-51.
Tanentzapf, G., Smith, C., McGlade, J. and Tepass, U. (2000). Apical, lateral, and basal polarization cues contribute to the development of the follicular epithelium during Drosophila oogenesis. J Cell Biol 151, 891-904.
Taylor, J., Abramova, N., Charlton, J. and Adler, P. N. (1998). Van Gogh: a new Drosophila tissue polarity gene. Genetics 150, 199-210.
Tepass, U. and Hartenstein, V. (1994). The development of cellular junctions in the Drosophila embryo. Dev Biol 161, 563-96.
Tepass, U., Tanentzapf, G., Ward, R. and Fehon, R. (2001). Epithelial cell polarity and cell junctions in Drosophila. Annu Rev Genet 35, 747-84.
Tomlinson, A. and Struhl, G. (1999). Decoding vectorial information from a gradient: sequential roles of the receptors Frizzled and Notch in establishing planar polarity in the Drosophila eye. Development 126, 5725-38.
Usui, T., Shima, Y., Shimada, Y., Hirano, S., Burgess, R. W., Schwarz, T. L., Takeichi, M. and Uemura, T. (1999). Flamingo, a seven-pass transmembrane cadherin, regulates planar cell polarity under the control of Frizzled. Cell 98, 585-95.
van der Bliek, A. M. and Meyerowitz, E. M. (1991). Dynamin-like protein encoded by the Drosophila shibire gene associated with vesicular traffic. Nature 351, 411-4.
Voas, M. G. and Rebay, I. (2004). Signal integration during development: insights from the Drosophila eye. Dev Dyn 229, 162-75.
Waddell, S., Armstrong, J. D., Kitamoto, T., Kaiser, K. and Quinn, W. G. (2000). The amnesiac gene product is expressed in two neurons in the Drosophila brain that are critical for memory. Cell 103, 805-13.
Wallingford, J. B., Fraser, S. E. and Harland, R. M. (2002). Convergent extension: the molecular control of polarized cell movement during embryonic development. Dev Cell 2, 695-706.
Wei, S. Y., Escudero, L. M., Yu, F., Chang, L. H., Chen, L. Y., Ho, Y. H., Lin, C. M., Chou, C. S., Chia, W., Modolell, J. et al. (2005). Echinoid is a component of adherens junctions that cooperates with DE-Cadherin to mediate cell adhesion. Dev Cell 8, 493-504.
Wodarz, A., Hinz, U., Engelbert, M. and Knust, E. (1995). Expression of crumbs confers apical character on plasma membrane domains of ectodermal epithelia of Drosophila. Cell 82, 67-76.
Wodarz, A. and Nusse, R. (1998). Mechanisms of Wnt signaling in development. Annu Rev Cell Dev Biol 14, 59-88.
Wong, H. C., Bourdelas, A., Krauss, A., Lee, H. J., Shao, Y., Wu, D., Mlodzik, M., Shi, D. L. and Zheng, J. (2003). Direct binding of the PDZ domain of Dishevelled to a conserved internal sequence in the C-terminal region of Frizzled. Mol Cell 12, 1251-60.
Wong, L. L. and Adler, P. N. (1993). Tissue polarity genes of Drosophila regulate the subcellular location for prehair initiation in pupal wing cells. J Cell Biol 123, 209-21.
Wucherpfennig, T., Wilsch-Brauninger, M. and Gonzalez-Gaitan, M. (2003). Role of Drosophila Rab5 during endosomal trafficking at the synapse and evoked neurotransmitter release. J Cell Biol 161, 609-24.
Xu, C., Kauffmann, R. C., Zhang, J., Kladny, S. and Carthew, R. W. (2000). Overlapping activators and repressors delimit transcriptional response to receptor tyrosine kinase signals in the Drosophila eye. Cell 103, 87-97.
Zheng, L., Zhang, J. and Carthew, R. W. (1995). frizzled regulates mirror-symmetric pattern formation in the Drosophila eye. Development 121, 3045-55.