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

“Genetic and biochemical*Department of Immunology University Hospital studies have revealed the regions essential for interaction with Armadillo’s adherens junction partners (Orsulic3508 GA, Utrecht The Netherlands and Peifer, 1996a; Cox et al., 1996; Pai et al., 1996).”

“These responses require the cells to be connected by AJ”

“Scrib, like Crb, is not required for the early localization of basal Dlt or apical Arm during blastoderm formation, and scrib mutants do not exhibit the defective cellularization or precipitous loss of cell adhesion seen when Dlt or Arm, respectively, are depleted in the embry”

“Peifer and collaborators showed that armadillo (b-catenin) mutant embryos of Drosophila, which harbor only one E-cadherin allele, showed a less severe segment polarity phenotype than embryos with two cadherin alleles (Cox et al. 1996).”

“…a clear role for catenins and the b-catenin–binding domain in cadherin-based adhesion (Nagafuchi and Takeichi, 1988, 1989; Ozawa et al., 1990; Hirano et al., 1992; Kintner, 1992; Hermiston and Gordon, 1995; Lee and Gumbiner, 1995; Cox et al., 1996; Kofron et al., 1997; Torres et al., 1997).”

“Conversely, experimental reduction of cadherin levels in Drosophila can lead to enhanced -catenin (armadillo) signaling activity (Cox et al., 1996).”

“The CCC is essential in the female germline and thus embryos that lack the maternal components of either DE-cadherin or Arm cannot be studied (27, 48, 105, 110, 152, 173) (mutations for Dα-catenin and Dp120 ctn are currently not available).”

“Partial loss-of-function mutants in the Drosophila -catenin (Armadillo [Arm]), such as arm043A01, result in lower levels of Arm, E-cadherin, and -catenin at the cell surface (Cox et al., 1996; Sokac and Wieschaus, 2008; Sawyer et al., 2009).”

“By sequestering -catenin at the membrane, cadherins modulate the signaling properties of cytosolic -catenin, creating a finely tuned balance between Wnt signaling and cell– cell adhesion (Heasman et al., 1994; Cox et al., 1996; Fagotto et al., 1996).”

“We tested whether formation of the primitive zonula adherens is required for the localization of Baz by examining arm XP33 M/Z mutants, which are defective in the early stages of zonula adherens formatio”

“Gene inactivation of armadillo/b-catenin in Drosophila (Cox et al., 1996; Müller and Wieschaus, 1996), aE-catenin, E-cadherin, and b-catenin in mouse (Larue et al., 1994; Haegel et al., 1995; Torres et al., 1997), and EP-cadherin and a-catenin in Xenopus (Heasman et al., 1994; Kafron et al., 1997)…”

“Germline clones of this class of alleles produce sufficient levels of Arm function to enable a few eggs to complete oogenesis but subsequent function of Arm in the embryo is severely compromised and these embryos fail to assemble apical adherens junctions (Cox et al., 1996; Tolwinski and Wieschaus, 2004).”

“The function of Arm in adherens junction formation is also being reported by Cox et al. (1996) with similar results.”

“A series of genetic and biochemical studies have identified -catenin as a central player of the wnt/wingless signal transduction cascade, which is important for pattern formation and axis determination during early development of invertebrate and vertebrate organisms (Kelly et al., 1995; Cox et al., 1996; Willert and…”

“The similarity between the defects in baz GLC embryos and embryos in which Arm has been severely deplete”

“, 1999), whereas reduction in the expression of cadherins in Drosophila embryos can enhance -catenin signaling (Cox et al., 1996).”

“, 1994), while in Drosophila, reduction in DE-cadherin levels enhances Armadillo's role in Wingless signaling (Cox et al., 1996).”

“␤-Catenin binding and clustering at cadherin intracellular domains are common to all classic cadherin-mediated junctions and are, in fact, required for adhesion (Ozawa et al., 1990; Gumbiner and McCrea, 1993; Peifer et al., 1993; Oyama et al., 1994; Haegel et al., 1995; Cox et al., 1996).”

“Brains and imaginal discs were dissected in Schneider’s Medium (Sigma-Aldrich), fixed for 20 min in 4% formaldehyde, and stained as described previously (Cox et al., 1996).”

“These epithelial balls may secrete cuticle into their lumens and produce the cuticle scraps observed in the terminal armm/z mutant phenotype (Cox et al., 1996), as polarized epithelial cysts have been proposed to do in crb mutants (Tanentzapf and Tepass, 2003).”

“The segment polarity defect of a weak armadillo allele can be partially rescued by making the flies heterozygous for DE-cadherin (Cox et al., 1996).”

“…associated with a number of genes re- quired for cellularization have been attributed to cy- required for the formation of the zonula adherens (Cox et al., 1996; Muller and Wieschaus, 1996).toskeletal defects (Foe et al., 1993; Schejter and The subcellular localization of DLT to the…”

“Germ-line clones mutant for a moderate allele of armadillo which can overcome oogenesis fail to exhibit normal cell morphology at gastrulation (Cox et al., 1996).”

“β-catenin, an important component of adherens junctions (Cox et al., 1996), interacts with proteins of the TCF/LEF family to transduce Wnt signals (Peifer and Polakis, 2000).”

“Conversely, reductions in cadherin protein levels can enhance β-catenin signaling (14), suggesting that the absolute level of cadherins may set thresholds for Wnt signals.”

“Indeed, E-cadherin containing adhesion complexes are supposed to be one of the key regulators of the cytoplasmic -catenin pool [310].”

“A combination of maternal and zygotic nulls of armadillo disrupts formation of an organized epithelium early in Drosophila embryogenesis (Cox et al., 1996; Peifer et al., 1993).”

“Although reduction of total -catenin immunofluorescence is modest ( 43% reduction) even after 48 h, relatively small changes in total -catenin can have dramatic phenotypic consequences (Cox et al., 1996; Sanson et al., 1996), likely because -catenin resides in two distinct pools in cells (Nelson and Nusse, 2004).”

“In addition to their role in establishing and maintaining cell polarity (Cox et al., 1996; Muller and Wieschaus, 1996), cadherins and catenins are actively involved in signaling by epithelial cells.”

“Studies in genetically manipulatable nonvertebrate species as well as nonmammalian vertebrate organisms have shown that b -catenin–mediated signaling affects axis formation and cell fate specification (McCrea et al., 1993; Heasman et al., 1994; Funayama et al., 1995; Cox et al., 1996; Molenaar et al., 1996).”

“Embryos mutant for the intermediate allele armXP33 show a dramatic and rapid collapse of the ectodermal epithelium at gastrulation after the blastoderm epithelium has been established (Cox et al., 1996; Müller and Wieschaus, 1996).”

“Moreover, several recent studies have demonstrated that both b-catenin and Armadillo can function as a transcriptional activator when complexed to Lef/Tcf transcription factors (Molenaar et al., 1996; Korinek et al., 1997; Morin et al., 1997; van de Wetering et al., 1997).”

“Yet, the pools are not completely separated, since changes in E-cadherin expression can lead to changes in cytoplasmic -catenin (Heasman et al. 1994; Cox et al. 1996; Fagotto et al. 1996; Sanson et al. 1996; Orsulic et al. 1999) and tyrosine phosphorylation of -catenin seems to dissociate it from the adherens junction…”

“The effects of UAS-Sgg* expression were also suppressed by the loss of one copy of brm or 3144 GENES & DEVELOPMENT moira (mor), which encodes an essential component of the Brm complex (Crosby et al. 1999), or by coexpression of a dominant negative form of Brm (DN-Brm; Elfring et al. 1998; Fig.”

“Severe reduction in Drosophila Arm (Cox et al., 1996) or DE-cadherin (Tepass et al., 1996) function leads to early loss of epithelial integrity.”

“Cuticles of lethal progeny were processed as in Cox et al. (1996).”

“For visualization of Pnut and Sep1 by immunofluorescence , embryos were fixed as described by Cox et al. (1996), devitellinized by shaking in 1:1 methanol:heptane, and stained as described by Peifer et al. (1993).”

“However, armadillo is also involved in cell adhesion (Cox et al., 1996); one, therefore, has to be very”

“We observed similar defects in armXP33 maternal mutants that disrupt nurse cell dumping during oogenesis (Cox et al., 1996).”

“Indeed, gain- and loss-of-function studies support a model in which cadherins directly sequester -cat from the nucleus and serve as a sink for the Wnt-generated cytosolic pool of -cat (Heasman et al., 1994; Cox et al., 1996; Fagotto et al., 1996).”

“aTub–gal4 VP16 (15)) with males carrying UAS–btsz2, UAS–btsz2Glu (also called btsz2GluD3 UTR in Supplementary Fig.”

“(this junctional Armadillo functions in cellular adhesio”

“In Drosophila, mutants lacking core AJ components lose epithelial structure as epithelial rearrangements are initiated at gastrulation (Cox et al., 1996; Harris and Peifer, 2004; Muller and Wieschaus, 1996).”

“, 1994), or deletion of the b -catenin gene (Peifer et al., 1993 b ; Haegel et al., 1995; Cox et al., 1996) results in loss A.”

“The removal or the modulation of the binding properties of - or -catenin at the adhesion machinery results in a loss or impairment of calcium-dependent cell adhesion (Hirano et al., 1992; Heasman et al., 1994; Watabe et al., 1994; Haegel et al., 1995; Cox et al., 1996).”

“Experiments have shown that cell‐cell adhesion, cell polarity and cytoskeletal integrity are disrupted during Drosophila embryogenesis in the absence of Armadillo [ 3 ].”

“This model has received more extensive experimental validation— cadherin overexpression competes with Wnt signalling [3,68–70], whilst β ‑catenin transcriptional activity can be upregulated on loss of cad‑ herin [71–74].”

“2, compare H with I) or cellularization furrows (Cox et al., 1996) of arm XP33 mutants, suggesting that AJs are substantially disrupted.”

“The core components of AJs are cadherins, b-catenin (bcat-or its fly homolog Armadillo (Arm)), and a-catenin (reviewed in [5]).”

“Embryos produced from germline clones of weakarmadillomutants have defects in the formation of adherens junctions and enhanced zygotic defects in wingless signaling (Cox et al 1996).”

“, 1996), b -catenin ( armadillo ) (Peifer and Wieschaus, 1990; Peifer et al., 1993; Müller and Wieschaus, 1996; Cox et al., 1996), and numerous genes required for the establishment of the apical and basolateral membrane domains (Müller and Wieschaus, 1996; Grawe et al.”

“Together, these intra- and extracellular interactions provide the basis for many properties characteristic of the AJ (6, 9, 14, 22, 25, 32, 33).”

“In addition, small changes in b-catenin protein levels can correspond to dramatic tissue phenotypes known to rely on b-catenin signaling [30,31].”

“Canonical signaling could be mediating such a transition in the kidney, although this would be contrary to other data, where a loss of β-catenin is correlated with epithelialto-mesenchymal transition [65].”

“AJ formation requires Arm, which links E-cadherin to a-catenin and subsequently to the intracellular actin cytoskeleton [12,17,18].”

“In a previous study, a signal to the nucleus via -catenin was hypothesized to be controlled by E-cadherin because of the dual roles of -catenin: induction of the nuclear signal and cadherin-mediated adhesion at the plasma membrane (Cox et al., 1996; Gottardi et al., 2001).”

“…transmembrane protein and the cytoplasmic protein Armadillo, which encodes the Drosophila homolog of ␤-catenin, are structural components of adherens junctions that mediate cell-cell adhesion and communication (Peifer, 1993; Cox et al., 1996, 1999; Pai et al., 1996; Peifer and Polakis 2000).”

“Embryonic adherens junctions are established during cellularization, and total loss of cadherin-based adhesion results in catastrophic defects in epithelial architecture (Cox et al., 1996; Tepass et al., 1996).”

“Indeed, this was originally hypothesized when it was observed that altering cadherin levels affected CTNNB1 distribution [128 – 133].”