Armadillo is required for adherens junction assembly, cell polarity, and morphogenesis during Drosophila embryogenesis.

“In addition to a contractile actin-myosin network, apical constriction requires assembly of AJs at the apical cell cortex.(41,61) According to a simple purse-string model, myosin II-dependent sliding of actin filaments past each other induces contraction of a circumferential microfilament network, which reduces the ap…”

“Few data exist in animal models on the subcellular distribution of Armadillo/b-catenin and E-Cadherin in the context of their function, with notable exceptions [28,35,44–48].”

“This situation completely differed from that of embryos produced from germ-line clones mutant for intermediate alleles of arm and that of embryos in which a dominant-negative form of DE-cadherin was expressed (Cox et al. 1996; Wang et al. 2004; DawesHoang et al. 2005).”

“This will be done by the analysis of salivary gland invagination in embryos mutant for different components of adhesion junctions, such as DE-CADHERIN or p-CATENIN (reviewed in Cox et al, 1996; Knust and Leptin, 1996).”

“This is probably due to the requirement of Arm in cell adhesion or viability in addition to Wg signaling (Peifer et al., 1993; Cox et al., 1996; Wehrli and Tomlinson, 1998).”

“Loss of Armadillo, the fly ortholog of b-catenin, leads to disruption of polarity of the actin cytoskeleton (Cox et al., 1996).”

“As in mammalian epithelia [15,16], the main functional components of this complex in Drosophila are the transmembrane protein Ecadherin, a calcium-dependent trans-membrane adhesion molecule, and the catenins (Armadillo and α-catenin) that link E-cadherin to the actin cytoskeleton at the cytoplasmic side [17-22].”

“Therefore, we assessed constriction at the onset of ventral furrow formation by staining embryos for b-catenin, an integral intracellular component of the AJ (Cox et al. 1996).”

“Arm is an essential component of AJ and has been indicated to play an important role in the assembly of AJs in polarized epithelium [ 4 , 26].”

“For example, cadherins negatively regulate β-catenin by competing for interaction with Lef/Tcf factors and perhaps, by tethering β-catenin to the cell plasma membrane away from the nucleus (Cox et al., 1996; Fagotto et al., 1996; Heasman et al., 1994; Orsulic et al., 1999; Sanson et al., 1996).”

“The initial analysis of Ecad, Arm, and α -catenin fit this simple model: loss of each totally disrupted cell adhesion, and thus completely halted morphogenesis (Cox et al. , 1996; Müller and Wieschaus, 1996; Tepass et al. , 1996; Sarpal et al. , 2012).”

“…septate junctions (SJs) and adherens junction (AJ) are crucial for epithelial barrier function and cell adhesion in invertebrates, we examined the expression and localization of the conserved SJ protein Coracle and the AJ core component Armadillo in lower tubules following regeneration ( 10 , 11 ).”

“Consistent with this view, low concentrations drive Drosophila β-catenin to adherens junctions, implying a stronger binding affinity for cadherin [178].”

“5 The actin cytoskeleton is organized by the Rho GTPase and adherens junctions (Cox et al., 1996; Fox et al., 2005; Homem and Peifer, 2008; Muller and Wieschaus, 1996; Peifer et al., 1993) which are ultimately positioned between the core apical and basolateral polarity determinants.”

“Similarly, the C-terminal region does not appear to be required for adhesive interactions, and there are no known adherens junction proteins that bind in this region: Drosophila embryos containing a C-terminally deleted b-catenin show normal adherens junctions but are defective in Wnt signaling ( Cox et al. 1996 ).”

“However, specific symmetry breaking functions for E-cadherin have often been obscured by its essential role in cell/cell adhesion (Cox et al., 1996; Johnson et al., 1986; Peifer et al., 1993; Shirayoshi et al., 1983; Stephenson et al., 2010).”

“Arm is multifunctional and is involved in intracellular signaling, cytoskeletal regulation, and cell adhesion during embryogenesis (Peifer et al., 1993; Cox et al., 1996; Sanson et al., 1996).”

“Armadillo, the fly b-catenin, leads to disruption of polarity of the actin cytoskeleton (Cox et al., 1996).”

“During morphogenesis, retinal cells are interconnected by AJs, which consist of core components such as N-cadherin (N-cad), actin, and armadillo (Arm) (Cox, Kirkpatrick, and Peifer 1996; Tepass and Harris 2007).”

“Epithelia are tissues composed of cells that are organized in a sheet and held 44 together by junctions, which maintain the integrity of the tissue as well as the apical-basal polarity 45 of cells (Choi et al., 2013; Classen et al., 2005; Cox et al., 1996; Gumbiner, 2005; Harris and 46 Peifer 2005; Tepass, 1997; Wang…”

“During cellularization, Cno recruitment is unaffected by the loss of Arm, and instead requires the small GTPase Rap1 (Sawyer et al., 2009).”

“AJ proteins are not essential for syncytial divisions (Grevengoed et al., 2003), but in their absence cell adhesion and polarity are lost when gastrulation begins (Cox et al., 1996; Müller and Wieschaus, 1996; Sarpal et al., 2012; Tepass et al., 1996).”

“Chez la drosophile, c’est apparemment une constriction apicale qui contraint les cellules à s’invaginer (figure 6) [32, 33].”

“Armadillo, the Drosophila -catenin homolog, degraded from the inherited pool with a half-life of 4.6 hours while its total abundance rose in the control channels, consistent with its roles in Wingless signaling and adherens-junction assembly 84,85 .”

“To visualize the epidermis, we used a GFP-tagged version of Armadillo, the fly homolog of beta-catenin and an adherens-junction marker (Cox et al., 1996).”

“Arm plays an essential role in the assembly of apicolateral cell adherens junctions, and is therefore normally apicolaterally localized 24,25 .”

“Cell adhesion is crucial in morphogenesis and when disrupted, results in metastatic cancer [78].”

“However, in embryos derived from germline clones of strong β-catenin mutants ( arm ) that also lack zygotic β-catenin, embryonic tissues lose their epithelial characteristics at gastrulation, producing unpolarised mesenchymal cells (Cox et al., 1996).”

“E-Cadherin is involved in multiple biological processes, including establishing and maintaining cell adhesion [10, 11], cell migration [12] and spindle orientation [13].”

“16 Apoptosis is a genetically controlled programmed cell death that plays an important role in many physiological and pathological events.”

“A crb-like phenotype has been documented for only a small number of genes that encode apical polarity proteins such as crb and stardust (sdt), or genes encoding AJ proteins such as bazooka (baz), shotgun (encoding DEcad) or armadillo (arm; Drosophila β-catenin) (Tepass et al., 1990, Tepass and Knust, 1990; 1993; Tepas…”

“While adherens junctions are known to be essential for epithelial cell shape [29-32], their exact role in polarisation of epithelial polarity determinants is still unclear.”

“…and Dlg and the simultaneous loss of Elav in the later larval stages in the l(3)tb mutants may be due to disassembly of the adherens junctions (Cox et al, 1996) thereby affecting cell-cell adhesion between glial and neuronal bodies in the brain and in the over-proliferative cells of the wing…”

“Dès l’apparition du sillon les AJ se forment au niveau de la protrusion apicale de celui-ci (Fig.12), (Cox et al., 1996; Harris and Peifer, 2004; Harris and Peifer, 2005; Müller and Wieschaus, 1996; Tepass and Hartenstein, 1994).”

“16 component of the adherens junction protein complex [45].”

“, 2013) or β-Catenin (Peifer et al., 1993; Cox et al., 1996; Oda et al., 1997; White et al., 1998) results in numerous defects in oogenesis including aberrant follicle cell packaging of germline cysts, oocyte mispositioning, nurse cell cortical actin breakdown, disrupted cytoplasmic actin filament bundle formation, an…”