果蠅的成蟲複眼是由在幼蟲時期的單一層表皮細胞，經由廣泛地形態改變，進而形成正確地小眼排列方式所組成的。這些劇烈地細胞型態改變主要是由一群會與肌動蛋白相結合的蛋白質，透過重新調整細胞骨架蛋白的組成來達成。CAP/Capulet (Capt), Slingshot (Ssh) 和Cofilin/Twinstar (Tsr)都是屬於會利用與肌動蛋白相結合而限制肌動蛋白聚合成長鏈狀的相關蛋白質。在過去的研究中，透過低解析度的觀察下發現，當capt, ssh 和 tsr這三個基因產生突變時，會導致在果蠅不同組織內都會造成大量肌動蛋白的累積。在此篇論文中，我們利用果蠅幼蟲複眼的單層表皮細胞為模式，且在高解析度的情況下，分析比較這三個基因突變時所造成的影響。我們發現capt, ssh的突變在morphogenetic furrow (MF)上和之後會具有相似的表現型，但是tsr則不會有類似的情況產生。在capt, ssh這兩個基因突變的細胞內，我們都可以觀察到(1)具有六角形細胞外型且由不連續的adherens junctions(AJs)所包圍；(2)大量累積活化態的肌球蛋白和肌動蛋白，且兩者呈現互補的表現。我們進一步發現capt, ssh突變的表現型是與protein kinase A (PKA)的不活化以及Rho的活化有關。而肌動蛋白的累積則是和Hedgehog訊號傳遞下游分子Ci75的移除有關。相反地，capt, ssh卻又負向調控Ci155量的累積，並且作用於PKA對Ci155蛋白質水解過程的上游。與ssh不同的是，在capt突變的情況下可以觀察到大量活化態的Cofilin。雖然過去的研究都認為Capt的C端為主要的功能片段，我們發現當大量表現Capt的N端就可以使capt突變的現象恢復。因此我們認為Capt利用其N端來幫助Cofilin的再循環利用，而Ssh則是利用調控的Cofilin活化狀態，藉此共同影響藉由肌動蛋白的動態變化而改變細胞外型的MF的進行，如此才能在果蠅複眼發育中正確地篩選及排列小眼的相對位置，使其具有正確的功能。

The Drosophila compound eye is formed from a sheet of epithelial tissue that undergoes extensive morphogenesis to form a pattern of regularly spaced ommatidia. These dramatic cell shape changes are regulated by reorganization of cytoskeleton via various of actin-binding proteins (ABPs). CAP/Capulet (Capt), Slingshot (Ssh) and Cofilin/Twinstar (Tsr) are ABPs that restrict actin polymerization. Previously, it was shown that low resolution analyses of loss-of-function mutations in capt, ssh and tsr all show ectopic F-actin accumulation in various Drosophila tissues. Here, we compared their loss-of-function phenotype at single-cell resolution, using a sheet of epithelial cells in the Drosophila eye imaginal disc as a model system. Surprisingly, we found that capt and ssh, but not tsr, mutant cells within and posterior to the morphogenetic furrow (MF) shared similar phenotypes. The capt/ssh mutant cells possessed: (1) hexagonal cell packing with discontinuous adherens junctions(AJs); and (2) largely complementary accumulation of excessive phosphorylated myosin light chain (p-MLC) and F-actin rings at the apical cortex. We further showed that the capt/ssh mutant phenotypes depended on the inactivation of protein kinase A (PKA) and activation of Rho. We also found that the accumulation of F-actin is dependent on the removal of Ci75. Conversely, Capt/Ssh negatively regulated Ci155 levels within the MF at a step upstream of protein kinase A-mediated Ci155 proteolysis. Significantly, unlike ssh mutant cells, a marked reduction of phosphorylated cofilin (p-cofilin) was detected in capt mutant cells. Although most studies have focused on the role of the C-terminal actin-binding domain of Capt, we found that overexpressing the N-terminal region of Capt that recycles cofilin and a constitutively active form of cofilin rescued the capt and ssh mutant phenotypes. We conclude that Capt and Ssh act at distinct steps to recycle and dephosphorylate cofilin, respectively, and then alter the cell shape changes and progression of the MF that in turn precisely organize the pattern of ommatidia during Drosophila eye morphogenesis.

Arber, S., Barbayannis, F. A., Hanser, H., Schneider, C., Stanyon, C. A., Bernard, O. and Caroni, P. (1998). Regulation of actin dynamics through phosphorylation of cofilin by LIM-kinase. Nature 393, 805-9.
Baker, N. E., Bhattacharya, A. and Firth, L. C. (2009). Regulation of Hh signal transduction as Drosophila eye differentiation progresses. Dev Biol 335, 356-66.
Balcer, H. I., Goodman, A. L., Rodal, A. A., Smith, E., Kugler, J., Heuser, J. E. and Goode, B. L. (2003). Coordinated regulation of actin filament turnover by a high-molecular-weight Srv2/CAP complex, cofilin, profilin, and Aip1. Curr Biol 13, 2159-69.
Baum, B., Li, W. and Perrimon, N. (2000). A cyclase-associated protein regulates actin and cell polarity during Drosophila oogenesis and in yeast. Curr Biol 10, 964-73.
Benlali, A., Draskovic, I., Hazelett, D. J. and Treisman, J. E. (2000). act up controls actin polymerization to alter cell shape and restrict Hedgehog signaling in the Drosophila eye disc. Cell 101, 271-81.
Carlier, M. F., Laurent, V., Santolini, J., Melki, R., Didry, D., Xia, G. X., Hong, Y., Chua, N. H. and Pantaloni, D. (1997). Actin depolymerizing factor (ADF/cofilin) enhances the rate of filament turnover: implication in actin-based motility. J Cell Biol 136, 1307-22.
Cavey, M., Rauzi, M., Lenne, P. F. and Lecuit, T. (2008). A two-tiered mechanism for stabilization and immobilization of E-cadherin. Nature 453, 751-6.
Chan-Yen Ou, H. P. a. C.-T. C. (2003). Control of protein degradation by E3 ubiquitin ligases in Drosophila eye development. TRENDS in Genetics 19, 382-389
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.
Chanut, F. and Heberlein, U. (1995). Role of the morphogenetic furrow in establishing polarity in the Drosophila eye. Development 121, 4085-94.
Chen, J., Godt, D., Gunsalus, K., Kiss, I., Goldberg, M. and Laski, F. A. (2001). Cofilin/ADF is required for cell motility during Drosophila ovary development and oogenesis. Nat Cell Biol 3, 204-9.
Corrigall, D., Walther, R. F., Rodriguez, L., Fichelson, P. and Pichaud, F. (2007). Hedgehog signaling is a principal inducer of Myosin-II-driven cell ingression in Drosophila epithelia. Dev Cell 13, 730-42.
Dominguez, M. and Hafen, E. (1997). Hedgehog directly controls initiation and propagation of retinal differentiation in the Drosophila eye. Genes Dev 11, 3254-64.
dos Remedios, C. G., Chhabra, D., Kekic, M., Dedova, I. V., Tsubakihara, M., Berry, D. A. and Nosworthy, N. J. (2003). Actin binding proteins: regulation of cytoskeletal microfilaments. Physiol Rev 83, 433-73.
Escudero, L. M., Bischoff, M. and Freeman, M. (2007). Myosin II regulates complex cellular arrangement and epithelial architecture in Drosophila. Dev Cell 13, 717-29.
Fernandez, B. G., Gaspar, P., Bras-Pereira, C., Jezowska, B., Rebelo, S. R. and Janody, F. (2011). Actin-Capping Protein and the Hippo pathway regulate F-actin and tissue growth in Drosophila. Development 138, 2337-46.
Fox, D. T. and Peifer, M. (2007). Abelson kinase (Abl) and RhoGEF2 regulate actin organization during cell constriction in Drosophila. Development 134, 567-78.
Freeman, N. L., Chen, Z., Horenstein, J., Weber, A. and Field, J. (1995). An actin monomer binding activity localizes to the carboxyl-terminal half of the Saccharomyces cerevisiae cyclase-associated protein. J Biol Chem 270, 5680-5.
Fu, W. and Baker, N. E. (2003). Deciphering synergistic and redundant roles of Hedgehog, Decapentaplegic and Delta that drive the wave of differentiation in Drosophila eye development. Development 130, 5229-39.
Gieselmann, R. and Mann, K. (1992). ASP-56, a new actin sequestering protein from pig platelets with homology to CAP, an adenylate cyclase-associated protein from yeast. FEBS Lett 298, 149-53.
Goode, B. L., Drubin, D. G. and Lappalainen, P. (1998). Regulation of the cortical actin cytoskeleton in budding yeast by twinfilin, a ubiquitous actin monomer-sequestering protein. J Cell Biol 142, 723-33.
Gottwald, U., Brokamp, R., Karakesisoglou, I., Schleicher, M. and Noegel, A. A. (1996). Identification of a cyclase-associated protein (CAP) homologue in Dictyostelium discoideum and characterization of its interaction with actin. Mol Biol Cell 7, 261-72.
Greenwood, S. and Struhl, G. (1999). Progression of the morphogenetic furrow in the Drosophila eye: the roles of Hedgehog, Decapentaplegic and the Raf pathway. Development 126, 5795-808.
Grosshans, J., Wenzl, C., Herz, H. M., Bartoszewski, S., Schnorrer, F., Vogt, N., Schwarz, H. and Muller, H. A. (2005). RhoGEF2 and the formin Dia control the formation of the furrow canal by directed actin assembly during Drosophila cellularisation. Development 132, 1009-20.
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.
Ho, Y. H., Lien, M. T., Lin, C. M., Wei, S. Y., Chang, L. H. and Hsu, J. C. (2010). Echinoid regulates Flamingo endocytosis to control ommatidial rotation in the Drosophila eye. Development 137, 745-54.
Hou, X. S., Chou, T. B., Melnick, M. B. and Perrimon, N. (1995). The torso receptor tyrosine kinase can activate Raf in a Ras-independent pathway. Cell 81, 63-71.
Ichetovkin, I., Grant, W. and Condeelis, J. (2002). Cofilin produces newly polymerized actin filaments that are preferred for dendritic nucleation by the Arp2/3 complex. Curr Biol 12, 79-84.
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.
Janody, F. and Treisman, J. E. (2006). Actin capping protein alpha maintains vestigial-expressing cells within the Drosophila wing disc epithelium. Development 133, 3349-57.
Jarman, A. P., Grell, E. H., Ackerman, L., Jan, L. Y. and Jan, Y. N. (1994). Atonal is the proneural gene for Drosophila photoreceptors. Nature 369, 398-400.
Lappalainen, P. and Drubin, D. G. (1997). Cofilin promotes rapid actin filament turnover in vivo. Nature 388, 78-82.
Lee, A. and Treisman, J. E. (2004). Excessive Myosin activity in mbs mutants causes photoreceptor movement out of the Drosophila eye disc epithelium. Mol Biol Cell 15, 3285-95.
Lee, T. and Luo, L. (1999). Mosaic analysis with a repressible cell marker for studies of gene function in neuronal morphogenesis. Neuron 22, 451-61.
Li, W., Ohlmeyer, J. T., Lane, M. E. and Kalderon, D. (1995). Function of protein kinase A in hedgehog signal transduction and Drosophila imaginal disc development. Cell 80, 553-62.
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.
Major, R. J. and Irvine, K. D. (2005). Influence of Notch on dorsoventral compartmentalization and actin organization in the Drosophila wing. Development 132, 3823-33.
Martin, A. C. (2010). Pulsation and stabilization: Contractile forces that underlie morphogenesis. Developmental Biology 341, 114-125.
Medeiros, N. A., Burnette, D. T. and Forscher, P. (2006). Myosin II functions in actin-bundle turnover in neuronal growth cones. Nat Cell Biol 8, 215-26.
Methot, N. and Basler, K. (1999). Hedgehog controls limb development by regulating the activities of distinct transcriptional activator and repressor forms of Cubitus interruptus. Cell 96, 819-31.
Moriyama, K. and Yahara, I. (2002). Human CAP1 is a key factor in the recycling of cofilin and actin for rapid actin turnover. J Cell Sci 115, 1591-601.
Nagata-Ohashi, K., Ohta, Y., Goto, K., Chiba, S., Mori, R., Nishita, M., Ohashi, K., Kousaka, K., Iwamatsu, A., Niwa, R. et al. (2004). A pathway of neuregulin-induced activation of cofilin-phosphatase Slingshot and cofilin in lamellipodia. J Cell Biol 165, 465-71.
Nishida, E. (1985). Opposite effects of cofilin and profilin from porcine brain on rate of exchange of actin-bound adenosine 5'-triphosphate. Biochemistry 24, 1160-4.
Niwa, R., Nagata-Ohashi, K., Takeichi, M., Mizuno, K. and Uemura, T. (2002). Control of actin reorganization by Slingshot, a family of phosphatases that dephosphorylate ADF/cofilin. Cell 108, 233-46.
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.
Oser, M. and Condeelis, J. (2009). The cofilin activity cycle in lamellipodia and invadopodia. J Cell Biochem 108, 1252-62.
Ou, C. Y., Lin, Y. F., Chen, Y. J. and Chien, C. T. (2002). Distinct protein degradation mechanisms mediated by Cul1 and Cul3 controlling Ci stability in Drosophila eye development. Genes Dev 16, 2403-14.
Paavilainen, V. O., Bertling, E., Falck, S. and Lappalainen, P. (2004). Regulation of cytoskeletal dynamics by actin-monomer-binding proteins. Trends Cell Biol 14, 386-94.
Pappu, K. S., Chen, R., Middlebrooks, B. W., Woo, C., Heberlein, U. and Mardon, G. (2003). Mechanism of hedgehog signaling during Drosophila eye development. Development 130, 3053-62.
Pollard, T. D. (2003). The cytoskeleton, cellular motility and the reductionist agenda. Nature 422, 741-5.
Quintero-Monzon, O., Jonasson, E. M., Bertling, E., Talarico, L., Chaudhry, F., Sihvo, M., Lappalainen, P. and Goode, B. L. (2009). Reconstitution and dissection of the 600-kDa Srv2/CAP complex: roles for oligomerization and cofilin-actin binding in driving actin turnover. J Biol Chem 284, 10923-34.
Rogers, S. L., Wiedemann, U., Stuurman, N. and Vale, R. D. (2003). Molecular requirements for actin-based lamella formation in Drosophila S2 cells. J Cell Biol 162, 1079-88.
Sai, X. and Ladher, R. K. (2008). FGF signaling regulates cytoskeletal remodeling during epithelial morphogenesis. Curr Biol 18, 976-81.
Sansores-Garcia, L., Bossuyt, W., Wada, K., Yonemura, S., Tao, C., Sasaki, H. and Halder, G. (2010). Modulating F-actin organization induces organ growth by affecting the Hippo pathway. EMBO J 30, 2325-35.
Sascha Hilgenfeldt, S. E., and Richard W. Carthew. (2008). Physical modeling of cell geometric order in an epithelial tissue. PNAS 105 907-911
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.
Tomlinson, A. (1988). Cellular interactions in the developing Drosophila eye. Development 104, 183-93.
Vallotton, P., Gupton, S. L., Waterman-Storer, C. M. and Danuser, G. (2004). Simultaneous mapping of filamentous actin flow and turnover in migrating cells by quantitative fluorescent speckle microscopy. Proc Natl Acad Sci U S A 101, 9660-5.
Wang, D., Zhang, L., Zhao, G., Wahlstrom, G., Heino, T. I., Chen, J. and Zhang, Y. Q. (2010). Drosophila twinfilin is required for cell migration and synaptic endocytosis. J Cell Sci 123, 1546-56.
Wilson, C. A., Tsuchida, M. A., Allen, G. M., Barnhart, E. L., Applegate, K. T., Yam, P. T., Ji, L., Keren, K., Danuser, G. and Theriot, J. A. (2010). Myosin II contributes to cell-scale actin network treadmilling through network disassembly. Nature 465, 373-7.
Wilson, C. W. and Chuang, P. T. (2010). Mechanism and evolution of cytosolic Hedgehog signal transduction. Development 137, 2079-94.
Yang, N., Higuchi, O., Ohashi, K., Nagata, K., Wada, A., Kangawa, K., Nishida, E. and Mizuno, K. (1998). Cofilin phosphorylation by LIM-kinase 1 and its role in Rac-mediated actin reorganization. Nature 393, 809-12.
Zelicof, A., Protopopov, V., David, D., Lin, X. Y., Lustgarten, V. and Gerst, J. E. (1996). Two separate functions are encoded by the carboxyl-terminal domains of the yeast cyclase-associated protein and its mammalian homologs. Dimerization and actin binding. J Biol Chem 271, 18243-52.