Expression Of DE-cadherin Research Articles

Pvr receptor tyrosine kinase signaling promotes post-embryonic morphogenesis, and survival of glia and neural progenitor cells in Drosophila.

Stem cells reside in specialized microenvironments, called niches, that regulate their development and the development of their progeny. However, the development and maintenance of niches are poorly understood. In the Drosophila brain, cortex glial cells provide a niche that promotes self-renewal and proliferation of neural stem cell-like cells (neuroblasts). In the central brain, neuroblasts and their progeny control post-embryonic morphogenesis of cortex glia through PDGF-like ligands, and this PDGFR receptor tyrosine kinase (RTK) signaling in cortex glia is required for expression of DE-cadherin, which sustains neuroblasts. Thus, through an RTK-dependent feed-forward loop, neuroblasts and their glial niche actively maintain each other. When the EGFR RTK is constitutively activated in cortex glia, they overexpress PDGF orthologs to stimulate autocrine PDGFR signaling, which uncouples their growth and survival from neuroblasts, and drives neoplastic glial transformation and elimination of neuroblasts. These results provide fundamental insights into glial development and niche regulation, and show that niche-neural stem cell feed-forward signaling becomes hijacked to drive neural tumorigenesis.

Ovarian polarity and cell shape determination by Btk29A in Drosophila.

Drosophila Btk29A is a Tec family nonreceptor tyrosine kinase, the ortholog of which causes X-linked agammaglobulinemia in humans when mutant. In Btk29AficP mutant ovaries, multiple defects are observed: extrapolar cells form ectopically; osk mRNA fails to accumulate posteriorly in mature oocytes; the shape and alignment of follicle cells are grossly distorted. All these phenotypes are rescued by selectively overexpressing the type 2 isoform of wild-type Btk29A in follicle cells. Expression of certain proteins enriched in adherens junctions is markedly affected in Btk29AficP mutants; the anterior-posterior gradient normally observed in the expression of DE-Cadherin and Armadillo are lost and Canoe is sequestered from adherens junctions. Intriguingly, tyrosine phosphorylation of Canoe is reduced in Btk29AficP mutants. It is proposed that Btk29A is required for the establishment of egg chamber polarity presumably through the regulation of subcellular localization of its downstream proteins, including Cno.

Poly(ADP-ribose) glycohydrolase and poly(ADP-ribose)-interacting protein Hrp38 regulate pattern formation during Drosophila eye development

Drosophila Hrp38, a homolog of human hnRNP A1, has been shown to regulate splicing, but its function can be modified by poly(ADP-ribosyl)ation. Notwithstanding such findings, our understanding of the roles of poly(ADP-ribosyl)ated Hrp38 on development is limited. Here, we have demonstrated that Hrp38 is essential for fly eye development based on a rough-eye phenotype with disorganized ommatidia observed in adult escapers of the hrp38 mutant. We also observed that poly(ADP-ribose) glycohydrolase (Parg) loss-of-function, which caused increased Hrp38 poly(ADP-ribosyl)ation, also resulted in the rough-eye phenotype with disrupted ommatidial lattice and reduced number of photoreceptor cells. In addition, ectopic expression of DE-cadherin, which is required for retinal morphogenesis, fully rescued the rough-eye phenotype of the hrp38 mutant. Similarly, Parg mutant eye clones had decreased expression level of DE-cadherin with orientation defects, which is reminiscent of DE-cadherin mutant eye phenotype. Therefore, our results suggest that Hrp38 poly(ADP-ribosyl)ation controls eye pattern formation via regulation of DE-cadherin expression, a finding which has implications for understanding the pathogenic mechanisms of Hrp38-related Fragile X syndrome and PARP1-related retinal degeneration diseases.

Genetic Analysis of Fibroblast Growth Factor Signaling in theDrosophilaEye

The development of eyes in Drosophila involves intricate epithelial reorganization events for accurate positioning of cells and proper formation and organization of ommatidial clusters. We demonstrate that Branchless (Bnl), the fibroblast growth factor ligand, regulates restructuring events in the eye disc primordium from as early as the emergence of clusters from a morphogenetic front to the cellular movements during pupal eye development. Breathless (Btl) functions as the fibroblast growth factor receptor to mediate Bnl signal, and together they regulate expression of DE-cadherin, Crumbs, and Actin. In addition, in the eye Bnl regulates the temporal onset and extent of retinal basal glial cell migration by activating Btl in the glia. We hypothesized that the Bnl functions in the eye are Hedgehog dependent and represent novel aspects of Bnl signaling not explored previously.

P67. Conversion of Drosophila neuroepithelial stem cells into neuroblasts occurs during prolonged G1 phase, whose timing is regulated by Notch signaling

Postembryonic neuroepithelial stem cells (NESCs) in the outer proliferation center (OPC) of the Drosophila optic lobe initially divide symmetrically to expand the pool of stem or progenitor cells, and are consequently converted into postembryonic neuroblasts (pNBs). pNBs generate both progenitor cells (pNBs) and differentiating cells (GMCs; ganglion mother cells) by asymmetric division, the latter of which then generate two neurons. Thus far the mechanism underlying the conversion of NESCs into pNBs has been unknown. We have shown that the NESCs dividing symmetrically at the border between NESCs and pNBs generate two NESCs, one of which is then converted into pNB during G1 phase by losing epithelial features including belted adherence junction (AJ) and high level of DE-cadherin expression at the AJ, which is followed by upregulation of pan-neural gene Asense. We found that Notch signaling is activated just before the start of conversion and rapidly downregulated upon completion of the conversion, which is marked by high level of Asense expression. Thus, we examined the role of Notch signaling in the conversion of NESCs by MARCM clonal analysis and found that Notch signaling regulates the timing of conversion through initiating morphological changes and upregulation of Asense in the NESCs.

Stabilization of the Actomyosin Ring Enables Spermatocyte Cytokinesis in Drosophila

The scaffolding protein anillin is required for completion of cytokinesis. Anillin binds filamentous (F) actin, nonmuscle myosin II, and septins and in cell culture models has been shown to restrict actomyosin contractility to the cleavage furrow. Whether anillin also serves this function during the incomplete cytokinesis that occurs in developing germ cells has remained unclear. Here, we show that anillin is required for cytokinesis in dividing Drosophila melanogaster spermatocytes and that anillin, septins, and myosin II stably associate with the cleavage furrow in wild-type cells. Anillin is necessary for recruitment of septins to the cleavage furrow and for maintenance of F-actin and myosin II at the equator in late stages of cytokinesis. Remarkably, expression of DE-cadherin suppresses the cytokinesis defect of anillin-depleted spermatocytes. DE-cadherin recruits beta-catenin (armadillo) and alpha-catenin to the cleavage furrow and stabilizes F-actin at the equator. Similarly, E-cadherin expression suppresses the cytokinesis defect caused by anillin knockdown in mouse L-fibroblast cells. Our results show that the anillin-septin and cadherin-catenin complexes can serve as alternative cassettes to promote tight physical coupling of F-actin and myosin II to the cleavage furrow and successful completion of cytokinesis.

Regulation of cell shape, wing hair initiation and the actin cytoskeleton by Trc/Fry and Wts/Mats complexes

The two NDR kinase family genes in Drosophila are tricornered ( trc) and warts ( wts). Previous studies on trc have focused on its role in the morphogenesis of extensions of epidermal cells and in dendrite branching and tiling. Studies on wts have focused on its roles as a tumor suppressor, in controlling photoreceptor type and in the maintenance of dendrites. Here we examine and compare the function of these genes in wing cells prior to their terminal differentiation. Mutations in these genes lead to changes in cell shape, cellular levels of F-actin, the timing of differentiation, and the expression of multiple wing hairs and DE-Cadherin. We showed that the effects of wts on all of these processes appear to be mediated by its regulation of the Yorkie transcription factor. We also provide evidence that trc regulates the expression of DE-cadherin and mwh. In addition, we showed that the effects on cell shape and the timing of differentiation appear to be not linked to changes in relative growth rate of cells compared to their neighbors.

Ras signaling modulates activity of the ecdysone receptor EcR during cell migration in the drosophila ovary

Ecdysone Receptor (EcR) mediates effects of the hormone ecdysone during larval molts, pupal metamorphosis, and adult female oogenesis. In the ovary, egg chamber formation requires interactions between the somatic follicle cell (FC) epithelium and the germ line nurse cell/oocyte cyst. Previous work has shown EcR is required in the germ line for egg chamber maturation, and here we examine EcR requirements in the FC at late stages of oogenesis. EcR protein is ubiquitous in the FC but its activity is restricted, visualized by activity of the "ligand sensor" hs-GAL4-EcR ligand binding domain fusion and EcRE-lacZ reporter gene expression. GAL4-EcR is activated in the FC by an ecdysone agonist and repressed by tissue-specific Ras GTPase signals. To determine the significance of restricted sites of EcR activity in the FC, we used targeted misexpression of the dominant negative EcR (EcR-DN) molecules EcR(F645A) and EcR(W650A). EcR-DN expression at stage 10 reduced EcRE-lacZ expression in the nurse cell FC and resulted in abnormal FC migrations, including aberrant centripetal migration and dorsal appendage tube formation, leading to the formation of cup-shaped eggs with shortened, branched dorsal appendages at stage 14. Clones of FC expressing EcR-DN displayed cell-autonomous increases in DE-cadherin expression and abnormal epithelial junction formation. EcR-DN expression caused thin eggshell phenotypes that correlated with both reduced levels of chorion gene expression and reduction in chorion gene amplification. Our results indicate that tissue-specific modulation of EcR activity by the Ras signaling pathway refines temporal ecdysone signals that regulate FC differentiation and cadherin-mediated epithelial cell shape changes.

Zinc transport activity of Fear of Intimacy is essential for proper gonad morphogenesis and DE-cadherin expression

Embryonic gonad formation involves intimate contact between germ cells and specialized somatic cells along with the complex morphogenetic movements necessary to create proper gonad architecture. Previously, we have shown that gonad formation in Drosophila requires the homophilic cell-adhesion molecule Drosophila E-cadherin (DE-cadherin), and also Fear of Intimacy (FOI), which is required for stable accumulation of DE-cadherin protein in the gonad. Here, we present an in vivo structure-function analysis of FOI that strongly indicates that zinc transport activity of FOI is essential for gonad development. Mutant forms of FOI that are defective for zinc transport also fail to rescue morphogenesis and DE-cadherin expression in the gonad. We further show that expression of DE-cadherin in the gonad is regulated post-transcriptionally and that foi affects this post-transcriptional control. Expression of DE-cadherin from a ubiquitous (tubulin) promoter still results in gonad-specific accumulation of DE-cadherin, which is strongly reduced in foi mutants. This work indicates that zinc is a crucial regulator of developmental processes and can affect DE-cadherin expression on multiple levels.

Fat and Wingless signaling oppositely regulate epithelial cell-cell adhesion and distal wing development inDrosophila

Development of organ-specific size and shape demands tight coordination between tissue growth and cell-cell adhesion. Dynamic regulation of cell adhesion proteins thus plays an important role during organogenesis. In Drosophila, the homophilic cell adhesion protein DE-Cadherin (DE-Cad) regulates epithelial cell-cell adhesion at adherens junctions (AJs). Here, we show that along the proximodistal (PD) axis of the developing wing epithelium, apical cell shapes and expression of DE-Cad are graded in response to Wingless (Wg), a morphogen secreted from the dorsoventral (DV) organizer in distal wing, suggesting a PD gradient of cell-cell adhesion. The Fat (Ft) tumor suppressor, by contrast, represses DE-Cad expression. In genetic tests, ft behaves as a suppressor of Wg signaling. Cytoplasmic pool of beta-catenin/Arm, the intracellular transducer of Wg signaling, is negatively correlated with the activity of Ft. Moreover, unlike that of Wg, signaling by Ft negatively regulates the expression of Distalless (Dll) and Vestigial (Vg). Finally, we show that Ft intersects Wnt/Wg signaling, downstream of the Wg ligand. Fat and Wg signaling thus exert opposing regulation to coordinate cell-cell adhesion and patterning along the PD axis of Drosophila wing.

Neuroglian and DE-Cadherin Activate Independent Cytoskeleton Assembly Pathways in Drosophila S2 Cells

The cytoskeletal proteins spectrin and ankyrin colocalize with sites of E-cadherin-mediated cell–cell adhesion in mammalian cells. Here we examined the effects of Drosophila DE-cadherin expression on spectrin and ankyrin in Drosophila S2 tissue culture cells. DE-cadherin caused a dramatic change in the cytoplasmic concentration and distribution of armadillo, the Drosophila homolog of β catenin. However, DE-cadherin expression had no detectable effect on the quantity or subcellular distribution of ankyrin or spectrin. In reciprocal experiments, recruitment of ankyrin and αβ spectrin to the plasma membrane by another cell adhesion molecule, neuroglian, had no effect on the quantity or distribution of armadillo. The results indicate that DE-cadherin–catenin complexes and neuroglian-spectrin/ankyrin complexes form by nonintersecting pathways. Recruitment of spectrin does not appear to be a conserved feature of DE-cadherin function.

DE-Cadherin is required for intercellular motility during Drosophila oogenesis.

Cadherins are involved in a variety of morphogenetic movements during animal development. However, it has been difficult to pinpoint the precise function of cadherins in morphogenetic processes due to the multifunctional nature of cadherin requirement. The data presented here indicate that homophilic adhesion promoted by Drosophila E-cadherin (DE-cadherin) mediates two cell migration events during Drosophila oogenesis. In Drosophila follicles, two groups of follicle cells, the border cells and the centripetal cells migrate on the surface of germline cells. We show that the border cells migrate as an epithelial patch in which two centrally located cells retain epithelial polarity and peripheral cells are partially depolarized. Both follicle cells and germline cells express DE-cadherin, and border cells and centripetal cells strongly upregulate the expression of DE-cadherin shortly before and during their migration. Removing DE-cadherin from either the follicle cells or the germline cells blocks migration of border cells and centripetal cells on the surface of germline cells. The function of DE-cadherin in border cells appears to be specific for migration as the formation of the border cell cluster and the adhesion between border cells are not disrupted in the absence of DE-cadherin. The speed of migration depends on the level of DE-cadherin expression, as border cells migrate more slowly when DE-cadherin activity is reduced. Finally, we show that the upregulation of DE-cadherin expression in border cells depends on the activity of the Drosophila C/EBP transcription factor that is essential for border cell migration.

Cadherin-mediated cell adhesion and cell motility in Drosophila trachea regulated by the transcription factor Escargot.

Coordination of cell motility and adhesion is essential for concerted movement of tissues during animal morphogenesis. The Drosophila tracheal network is formed by branching, migration and fusion of tubular ectodermal epithelia. Tracheal tip cells, located at the end of each branch that is going to fuse, extend filopodia to search for targets and later change their cell shape to a seamless ring to allow passage of lumen. The cell adhesion molecule DE-cadherin accumulates at the site of contact to form a ring that marks the site of lumen entry and is essential for the fusion. DE-cadherin expression in tip cells of a subset of branches is dependent on escargot, a zinc finger gene expressed in all tip cells. Such escargot mutant tip cells failed to adhere to each other and continued to search for alternative targets by extending long filopodia. We present evidence indicating escargot positively regulates transcription of the DE-cadherin gene, shotgun. Overexpression of DE-cadherin rescued the defect in one of the fusion points in escargot mutants, demonstrating an essential role of DE-cadherin in target recognition and identifying escargot as a key regulator of cell adhesion and motility in tracheal morphogenesis.

Zygotic Drosophila E-cadherin expression is required for processes of dynamic epithelial cell rearrangement in the Drosophila embryo.

Dynamic epithelial reorganization is essential for morphogenesis of various organs. In Drosophila embryos, for example the Malpighian tubule is generated by cellular rearrangement of a preexisting epithelium and the tracheal network is formed by outgrowth, branching, and fusion of epithelial vesicles. Here we report that the previously identified locus shotgun (shg) encodes DE-cadherin, an epithelial cell-cell adhesion molecule of the classic cadherin type and that zygotic shg mutations rather specifically impair processes of the dynamic epithelial morphogenesis. In the mutants, the Malpighian tubule disintegrated into small spherical structures, and the tracheal network formation was blocked in selected steps. The malformation of these organs could be rescued by overexpression of DE-cadherin cDNA under a heat shock promoter. Unexpectedly, the zygotic null condition did not severely affect general epithelial organization; most epithelial tissues maintained not only their cell-cell associations but also their apicobasal polarity in the mutants. The zygotic null mutant retained a certain level of maternally derived DE-cadherin molecules until the end of embryogenesis. These results suggest that zygotic DE-cadherin expression is critical for the rearrangement processes of epithelial cells, whereas the maternally derived DE-cadherin may serve only for the maintenance of the static architecture of the epithelia.