Publications

2012
Staley, B K, Irvine KD.  2012.  Hippo signaling in Drosophila: Recent advances and insights. Developmental Dynamics. 241:3-15.
Codelia, VA, Irvine KD.  2012.  Hippo Signaling Goes Long Range. Cell. 150:669-670.Website
Ishikawa, HO, Xu A, Ogura E, Manning G, Irvine KD.  2012.  The Raine Syndrome Protein FAM20C Is a Golgi Kinase That Phosphorylates Bio-Mineralization Proteins.. PLoS One. 7:e42988. AbstractWebsite
Raine syndrome is caused by mutations in FAM20C, which had been reported to encode a secreted component of bone and teeth. We found that FAM20C encodes a Golgi-localized protein kinase, distantly related to the Golgi-localized kinase Four-jointed. Drosophila also encode a Golgi-localized protein kinase closely related to FAM20C. We show that FAM20C can phosphorylate secreted phosphoproteins, including both Casein and members of the SIBLING protein family, which modulate biomineralization, and we find that FAM20C phosphorylates a biologically active peptide at amino acids essential for inhibition of biomineralization. We also identify autophosphorylation of FAM20C, and characterize parameters of FAM20C's kinase activity, including its Km, pH and cation dependence, and substrate specificity. The biochemical properties of FAM20C match those of an enzymatic activity known as Golgi casein kinase. Introduction of point mutations identified in Raine syndrome patients into recombinant FAM20C impairs its normal localization and kinase activity. Our results identify FAM20C as a kinase for secreted phosphoproteins and establish a biochemical basis for Raine syndrome.
2011
Mao, Y, Mulvaney J, Zakaria S, Yu T, Morgan K M, Allen S, Basson AM, Francis-West P, Irvine KD.  2011.  Characterization of a Dchs1 mutant mouse reveals requirements for Dchs1-Fat4 signaling during mammalian development. Development (Cambridge, England). 138:947-57. AbstractWebsite
The Drosophila Dachsous and Fat proteins function as ligand and receptor, respectively, for an intercellular signaling pathway that regulates Hippo signaling and planar cell polarity. Although gene-targeted mutations in two mammalian Fat genes have been described, whether mammals have a Fat signaling pathway equivalent to that in Drosophila, and what its biological functions might be, have remained unclear. Here, we describe a gene-targeted mutation in a murine Dachsous homolog, Dchs1. Analysis of the phenotypes of Dchs1 mutant mice and comparisons with Fat4 mutant mice identify requirements for these genes in multiple organs, including the ear, kidney, skeleton, intestine, heart and lung. Dchs1 and Fat4 single mutants and Dchs1 Fat4 double mutants have similar phenotypes throughout the body. In some cases, these phenotypes suggest that Dchs1-Fat4 signaling influences planar cell polarity. In addition to the appearance of cysts in newborn kidneys, we also identify and characterize a requirement for Dchs1 and Fat4 in growth, branching and cell survival during early kidney development. Dchs1 and Fat4 are predominantly expressed in mesenchymal cells in multiple organs, and mutation of either gene increases protein staining for the other. Our analysis implies that Dchs1 and Fat4 function as a ligand-receptor pair during murine development, and identifies novel requirements for Dchs1-Fat4 signaling in multiple organs.
Rauskolb, C, Pan G, Reddy BVVG, Oh H, Irvine KD.  2011.  Zyxin links fat signaling to the hippo pathway. PLoS Biology. 9:e1000624. AbstractWebsite
The Hippo signaling pathway has a conserved role in growth control and is of fundamental importance during both normal development and oncogenesis. Despite rapid progress in recent years, key steps in the pathway remain poorly understood, in part due to the incomplete identification of components. Through a genetic screen, we identified the Drosophila Zyxin family gene, Zyx102 (Zyx), as a component of the Hippo pathway. Zyx positively regulates the Hippo pathway transcriptional co-activator Yorkie, as its loss reduces Yorkie activity and organ growth. Through epistasis tests, we position the requirement for Zyx within the Fat branch of Hippo signaling, downstream of Fat and Dco, and upstream of the Yorkie kinase Warts, and we find that Zyx is required for the influence of Fat on Warts protein levels. Zyx localizes to the sub-apical membrane, with distinctive peaks of accumulation at intercellular vertices. This partially overlaps the membrane localization of the myosin Dachs, which has similar effects on Fat-Hippo signaling. Co-immunoprecipitation experiments show that Zyx can bind to Dachs and that Dachs stimulates binding of Zyx to Warts. We also extend characterization of the Ajuba LIM protein Jub and determine that although Jub and Zyx share C-terminal LIM domains, they regulate Hippo signaling in distinct ways. Our results identify a role for Zyx in the Hippo pathway and suggest a mechanism for the role of Dachs: because Fat regulates the localization of Dachs to the membrane, where it can overlap with Zyx, we propose that the regulated localization of Dachs influences downstream signaling by modulating Zyx-Warts binding. Mammalian Zyxin proteins have been implicated in linking effects of mechanical strain to cell behavior. Our identification of Zyx as a regulator of Hippo signaling thus also raises the possibility that mechanical strain could be linked to the regulation of gene expression and growth through Hippo signaling.
Oh, H, Irvine KD.  2011.  Cooperative Regulation of Growth by Yorkie and Mad through bantam. Developmental Cell. 20:109-22. AbstractWebsite
The Dpp and Fat-Hippo signaling pathways both regulate growth in Drosophila. Dpp is a BMP family ligand and acts via a Smad family DNA-binding transcription factor, Mad. Fat-Hippo signaling acts via a non-DNA-binding transcriptional coactivator protein, Yorkie. Here, we show that these pathways are directly interlinked. They act synergistically to promote growth, in part via regulation of the microRNA gene bantam, and their ability to promote growth is mutually dependent. Yorkie and Mad physically bind each other, and we identify a 410 bp minimal enhancer of bantam that responds to Yorkie:Mad in vivo and in cultured cells, and show that both Yorkie and Mad associate with this enhancer in vivo. Our results indicate that in promoting the growth of Drosophila tissues, Fat-Hippo and Dpp signaling contribute distinct subunits of a shared transcriptional activation complex, Yorkie:Mad.
Sun, G, Irvine KD.  2011.  Regulation of Hippo signaling by Jun kinase signaling during compensatory cell proliferation and regeneration, and in neoplastic tumors. Developmental biology. 350:139-51. AbstractWebsite
When cells undergo apoptosis, they can stimulate the proliferation of nearby cells, a process referred to as compensatory cell proliferation. The stimulation of proliferation in response to tissue damage or removal is also central to epimorphic regeneration. The Hippo signaling pathway has emerged as an important regulator of growth during normal development and oncogenesis from Drosophila to humans. Here we show that induction of apoptosis in the Drosophila wing imaginal disc stimulates activation of the Hippo pathway transcription factor Yorkie in surviving and nearby cells, and that Yorkie is required for the ability of the wing to regenerate after genetic ablation of the wing primordia. Induction of apoptosis activates Yorkie through the Jun kinase pathway, and direct activation of Jun kinase signaling also promotes Yorkie activation in the wing disc. We also show that depletion of neoplastic tumor suppressor genes, including lethal giant larvae and discs large, or activation of aPKC, activates Yorkie through Jun kinase signaling, and that Jun kinase activation is necessary, but not sufficient, for the disruption of apical-basal polarity associated with loss of lethal giant larvae. Our observations identify Jnk signaling as a modulator of Hippo pathway activity in wing imaginal discs, and implicate Yorkie activation in compensatory cell proliferation and disc regeneration.
Reddy, BVVG, Irvine KD.  2011.  Regulation of Drosophila glial cell proliferation by Merlin-Hippo signaling.. Development. 138:5201-5212.
2010
Staley, B K, Irvine KD.  2010.  Warts and yorkie mediate intestinal regeneration by influencing stem cell proliferation. Current biology : CB. 20:1580-7. AbstractWebsite
Homeostasis in the Drosophila midgut is maintained by stem cells [1, 2]. The intestinal epithelium contains two types of differentiated cells that are lost and replenished: enteroendocrine (EE) cells and enterocytes (ECs). Intestinal stem cells (ISCs) are the only cells in the adult midgut that proliferate [3, 4], and ISC divisions give rise to an ISC and an enteroblast (EB), which differentiates into an EC or an EE cell [3-5]. If the midgut epithelium is damaged, then ISC proliferation increases [6-12]. Damaged ECs express secreted ligands (Unpaired proteins) that activate Jak-Stat signaling in ISCs and EBs to promote their proliferation and differentiation [7, 9, 13, 14]. We show that the Hippo pathway components Warts and Yorkie mediate a transition from low- to high-level ISC proliferation to facilitate regeneration. The Hippo pathway regulates growth in diverse organisms and has been linked to cancer [15, 16]. Yorkie is activated in ECs in response to tissue damage or activation of the damage-sensing Jnk pathway. Activation of Yorkie promotes expression of unpaired genes and triggers a nonautonomous increase in ISC proliferation. Our observations uncover a role for Hippo pathway components in regulating stem cell proliferation and intestinal regeneration.
Simon, MA, Xu A, Ishikawa HO, Irvine KD.  2010.  Modulation of Fat:Dachsous binding by the cadherin domain kinase four-jointed. Current biology : CB. 20:811-7. AbstractWebsite
In addition to quantitative differences in morphogen signaling specifying cell fates, the vector and slope of morphogen gradients influence planar cell polarity (PCP) and growth. The cadherin Fat plays a central role in this process. Fat regulates PCP and growth through distinct downstream pathways, each involving the establishment of molecular polarity within cells. Fat is regulated by the cadherin Dachsous (Ds) and the protein kinase Four-jointed (Fj), which are expressed in gradients in many tissues. Previous studies have implied that Fat is regulated by the vector and slope of these expression gradients. Here, we characterize how cells interpret the Fj gradient. We demonstrate that Fj both promotes the ability of Fat to bind to its ligand Ds and inhibits the ability of Ds to bind Fat. Consequently, the juxtaposition of cells with differing Fj expression results in asymmetric Fat:Ds binding. We also show that the influence of Fj on Fat is a direct consequence of Fat phosphorylation and identify a phosphorylation site important for the stimulation of Fat:Ds binding by Fj. Our results define a molecular mechanism by which a morphogen gradient can drive the polarization of Fat activity to influence PCP and growth.
Reddy, BVVG, Rauskolb C, Irvine KD.  2010.  Influence of fat-hippo and notch signaling on the proliferation and differentiation of Drosophila optic neuroepithelia. Development (Cambridge, England). 137:2397-408. AbstractWebsite
The Drosophila optic lobe develops from neuroepithelial cells, which function as symmetrically dividing neural progenitors. We describe here a role for the Fat-Hippo pathway in controlling the growth and differentiation of Drosophila optic neuroepithelia. Mutation of tumor suppressor genes within the pathway, or expression of activated Yorkie, promotes overgrowth of neuroepithelial cells and delays or blocks their differentiation; mutation of yorkie inhibits growth and accelerates differentiation. Neuroblasts and other neural cells, by contrast, appear unaffected by Yorkie activation. Neuroepithelial cells undergo a cell cycle arrest before converting to neuroblasts; this cell cycle arrest is regulated by Fat-Hippo signaling. Combinations of cell cycle regulators, including E2f1 and CyclinD, delay neuroepithelial differentiation, and Fat-Hippo signaling delays differentiation in part through E2f1. We also characterize roles for Jak-Stat and Notch signaling. Our studies establish that the progression of neuroepithelial cells to neuroblasts is regulated by Notch signaling, and suggest a model in which Fat-Hippo and Jak-Stat signaling influence differentiation by their acceleration of cell cycle progression and consequent impairment of Delta accumulation, thereby modulating Notch signaling. This characterization of Fat-Hippo signaling in neuroepithelial growth and differentiation also provides insights into the potential roles of Yes-associated protein in vertebrate neural development and medullablastoma.
Oh, H, Irvine KD.  2010.  Yorkie: the final destination of Hippo signaling. Trends in Cell Biology. 20:410-7. AbstractWebsite
The Hippo signaling pathway is a key regulator of growth during animal development, whereas loss of normal Hippo pathway activity is associated with a wide range of cancers. Hippo signaling represses growth by inhibiting the activity of a transcriptional co-activator protein, known as Yorkie in Drosophila and Yap in vertebrates. In the 5 years since the first report linking Yorkie to Hippo signaling, intense interest in this pathway has led to rapid increases in our understanding of the action and regulation of Yorkie/Yap, which we review here. These studies have also emphasized the complexity of Yorkie/Yap regulation, including multiple, distinct mechanisms for repressing its transcriptional activity, and multiple DNA-binding partner proteins that can direct Yorkie to distinct downstream target genes.
2009
Mao, Y, Kucuk B, Irvine KD.  2009.  Drosophila lowfat, a novel modulator of Fat signaling. Development (Cambridge, England). 136:3223-33. AbstractWebsite
The Fat-Hippo-Warts signaling network regulates both transcription and planar cell polarity. Despite its crucial importance to the normal control of growth and planar polarity, we have only a limited understanding of the mechanisms that regulate Fat. We report here the identification of a conserved cytoplasmic protein, Lowfat (Lft), as a modulator of Fat signaling. Drosophila Lft, and its human homologs LIX1 and LIX1-like, bind to the cytoplasmic domains of the Fat ligand Dachsous, the receptor protein Fat, and its human homolog FAT4. Lft protein can localize to the sub-apical membrane in disc cells, and this membrane localization is influenced by Fat and Dachsous. Lft expression is normally upregulated along the dorsoventral boundary of the developing wing, and is responsible for elevated levels of Fat protein there. Levels of Fat and Dachsous protein are reduced in lft mutant cells, and can be increased by overexpression of Lft. lft mutant animals exhibit a wing phenotype similar to that of animals with weak alleles of fat, and lft interacts genetically with both fat and dachsous. These studies identify Lft as a novel component of the Fat signaling pathway, and the Lft-mediated elevation of Fat levels as a mechanism for modulating Fat signaling.
Oh, H, Reddy BVVG, Irvine KD.  2009.  Phosphorylation-independent repression of Yorkie in Fat-Hippo signaling. Developmental biology. 335:188-97. AbstractWebsite
The Fat-Hippo signaling pathway plays an important role in the regulation of normal organ growth during development, and in pathological growth during cancer. Fat-Hippo signaling controls growth through a transcriptional co-activator protein, Yorkie. A Fat-Hippo pathway has been described in which Yorkie is repressed by phosphorylation, mediated directly by the kinase Warts and indirectly by upstream tumor suppressors that promote Warts kinase activity. We present here evidence for an alternate pathway in which Yorkie activity is repressed by direct physical association with three other pathway components: Expanded, Hippo, and Warts. Each of these Yorkie repressors contains one or more PPXY sequence motifs, and associates with Yorkie via binding of these PPXY motifs to WW domains of Yorkie. This direct binding inhibits Yorkie activity independently from effects on Yorkie phosphorylation, and does so both in vivo and in cultured cell assays. These results emphasize the importance of the relative levels of Yorkie and its upstream tumor suppressors to Yorkie regulation, and suggest a dual repression model, in which upstream tumor suppressors can regulate Yorkie activity both by promoting Yorkie phosphorylation and by direct binding.
Feng, Y, Irvine KD.  2009.  Processing and phosphorylation of the Fat receptor. Proceedings of the National Academy of Sciences of the United States of America. AbstractWebsite
The Drosophila tumor suppressors fat and discs overgrown (dco) function within an intercellular signaling pathway that controls growth and polarity. fat encodes a transmembrane receptor, but post-translational regulation of Fat has not been described. We show here that Fat is subject to a constitutive proteolytic processing, such that most or all cell surface Fat comprises a heterodimer of stably associated N- and C-terminal fragments. The cytoplasmic domain of Fat is phosphorylated, and this phosphorylation is promoted by the Fat ligand Dachsous. dco encodes a kinase that influences Fat signaling, and Dco is able to promote the phosphorylation of the Fat intracellular domain in cultured cells and in vivo. Evaluation of dco mutants indicates that they affect Fat's influence on growth and gene expression but not its influence on planar cell polarity. Our observations identify processing and phosphorylation as post-translational modifications of Fat, correlate the phosphorylation of Fat with its activation by Dachsous in the Fat-Warts pathway, and enhance our understanding of the requirement for Dco in Fat signaling.
Anderson, KV, Irvine KD.  2009.  Developmental biology moves forward in the 21st century. Current opinion in genetics & development. 19:299-301.Website
Oh, H, Irvine KD.  2009.  In vivo analysis of Yorkie phosphorylation sites. Oncogene. 28:1916-27. AbstractWebsite
The co-activator Yorkie (Yki) mediates transcriptional regulation effected by the Drosophila Fat-Warts (Wts)-Hippo (Hpo) pathways. Yki is inhibited by Wts-mediated phosphorylation, and a Wts phosphorylation site at Ser168 has been identified. Here we identify two additional Wts phosphorylation sites on Yki, and examine the respective contribution of all three sites to Yki nuclear localization and activity. Our results show that although Ser168 is the most critical site, all three phosphorylation sites influence Yki localization and activity in vivo, and can be sites of regulation by Wts. Thus, investigations of the role of Yki and its mammalian homolog Yes-associated protein (YAP) in development and oncogenesis should include evaluations of additional sites. The WW domains of Yki are not required for its phosphorylation, but instead are positively required for its activity. We also identify two potential sites of phosphorylation by an unknown kinase, which could influence phosphorylation of Ser168 by Wts, suggesting that there are additional mechanisms for regulating Yki/YAP activity.
2008
Reddy, BVVG, Irvine KD.  2008.  The Fat and Warts signaling pathways: new insights into their regulation, mechanism and conservation. Development (Cambridge, England). 135:2827-38. AbstractWebsite
A cassette of cytoplasmic Drosophila tumor suppressors, including the kinases Hippo and Warts, has recently been linked to the transmembrane tumor suppressor Fat. These proteins act within interconnected signaling pathways, the principal functions of which are to control the growth and polarity of developing tissues. Recent studies have enhanced our understanding of the basis for signal transduction by Fat and Warts pathways, including the identification of a DNA-binding protein at the end of the pathway, have established the conservation of Fat and Warts signaling from flies to mammals, and have given us new insights into their regulation and biological functions.
Oh, H, Irvine KD.  2008.  In vivo regulation of Yorkie phosphorylation and localization. Development (Cambridge, England). 135:1081-8. AbstractWebsite
Yorkie (Yki), a transcription factor of the Fat and Hippo signaling pathways, is negatively regulated by the Warts kinase. Here, we use Phos-tag gels to characterize Warts-dependent phosphorylation of Yki in vivo, and show that Warts promotes phosphorylation of Yki at multiple sites. We also show that Warts inhibits Yki nuclear localization in vivo, and can promote binding of Yki to 14-3-3 proteins in cultured cells. In vivo assessment of the influence of individual upstream regulators of Warts reveals that some mutants (e.g. fat) have only partial effects on Yki phosphorylation, and weak effects on Yki localization, whereas other genotypes (e.g. ex fat double mutants) have stronger effects on both Yki phosphorylation and localization. We also identify serine 168 as a critical site through which negative regulation of Yki by Warts-mediated phosphorylation occurs, but find that this site is not sufficient to explain effects of Hippo signaling on Yki in vivo. These results identify modulation of subcellular localization as a mechanism of Yki regulation, and establish that this regulation occurs in vivo through multiple sites of Warts-dependent phosphorylation on Yki.
Ishikawa, HO, Takeuchi H, Haltiwanger RS, Irvine KD.  2008.  Four-jointed is a Golgi kinase that phosphorylates a subset of cadherin domains. Science. 321:401-4. AbstractWebsite
The atypical cadherin Fat acts as a receptor for a signaling pathway that regulates growth, gene expression, and planar cell polarity. Genetic studies in Drosophila identified the four-jointed gene as a regulator of Fat signaling. We show that four-jointed encodes a protein kinase that phosphorylates serine or threonine residues within extracellular cadherin domains of Fat and its transmembrane ligand, Dachsous. Four-jointed functions in the Golgi and is the first molecularly defined kinase that phosphorylates protein domains destined to be extracellular. An acidic sequence motif (Asp-Asn-Glu) within Four-jointed was essential for its kinase activity in vitro and for its biological activity in vivo. Our results indicate that Four-jointed regulates Fat signaling by phosphorylating cadherin domains of Fat and Dachsous as they transit through the Golgi.
Irvine, KD.  2008.  A notch sweeter. Cell. 132:177-9. AbstractWebsite
Notch is a key signaling protein mediating cell-fate decisions during development. In this issue, Acar et al. (2008) describe a new gene called rumi that is required for Notch signaling in Drosophila. This gene encodes an O-glucosyltransferase that attaches glucose sugars to serine residues in the multiple EGF domains of the extracellular region of Notch. This modification by Rumi likely influences Notch folding and trafficking.
Okajima, T, Reddy BVVG, Matsuda T, Irvine KD.  2008.  Contributions of chaperone and glycosyltransferase activities of O-fucosyltransferase 1 to Notch signaling. BMC Biology. 6:1. AbstractWebsite
BACKGROUND: O-fucosyltransferase1 (OFUT1) is a conserved ER protein essential for Notch signaling. OFUT1 glycosylates EGF domains, which can then be further modified by the N-acetylglucosaminyltransferase Fringe. OFUT1 also possesses a chaperone activity that promotes the folding and secretion of Notch. Here, we investigate the respective contributions of these activities to Notch signaling in Drosophila. RESULTS: We show that expression of an isoform lacking fucosyltransferase activity, Ofut1R245A, rescues the requirement for Ofut1 in embryonic neurogenesis. Lack of requirement for O-fucosylation is further supported by the absence of embryonic phenotypes in Gmd mutants, which lack all forms of fucosylation. Requirements for O-fucose during imaginal development were evaluated by characterizing clones of cells expressing only Ofut1R245A. These clones phenocopy fringe mutant clones, indicating that the absence of O-fucose is functionally equivalent to the absence of elongated O-fucose. CONCLUSION: Our results establish that Notch does not need to be O-fucosylated for fringe-independent Notch signaling in Drosophila; the chaperone activity of OFUT1 is sufficient for the generation of functional Notch.
Stolz, A, Haines N, Pich A, Irvine KD, Hokke CH, Deelder AM, Gerardy-Schahn R, Wuhrer M, Bakker H.  2008.  Distinct contributions of beta 4GalNAcTA and beta 4GalNAcTB to Drosophila glycosphingolipid biosynthesis. Glycoconjugate Journal. 25:167-75. AbstractWebsite
Drosophila melanogaster has two beta4-N-acetylgalactosaminyltransferases, beta4GalNAcTA and beta4GalNAcTB, that are able to catalyse the formation of lacdiNAc (GalNAcbeta,4GlcNAc). LacdiNAc is found as a structural element of Drosophila glycosphingolipids (GSLs) suggesting that beta4GalNAcTs contribute to the generation of GSL structures in vivo. Mutations in Egghead and Brainaic, enzymes that generate the beta4GalNAcT trisaccharide acceptor structure GlcNAcbeta,3Manbeta,4GlcbetaCer, are lethal. In contrast, flies doubly mutant for the beta4GalNAcTs are viable and fertile. Here, we describe the structural analysis of the GSLs in beta4GalNAcT mutants and find that in double mutant flies no lacdiNAc structure is generated and the trisaccharide GlcNAcbeta,3Manbeta,4GlcbetaCer accumulates. We also find that phosphoethanolamine transfer to GlcNAc in the trisaccharide does not occur, demonstrating that this step is dependent on prior or simultaneous transfer of GalNAc. By comparing GSL structures generated in the beta4GalNAcT single mutants we show that beta4GalNAcTB is the major enzyme for the overall GSL biosynthesis in adult flies. In beta4GalNAcTA mutants, composition of GSL structures is indistinguishable from wild-type animals. However, in beta4GalNAcTB mutants precursor structures are accumulating in different steps of GSL biosynthesis, without the complete loss of lacdiNAc, indicating that beta4GalNAcTA plays a minor role in generating GSL structures. Together our results demonstrate that both beta4GalNAcTs are able to generate lacdiNAc structures in Drosophila GSL, although with different contributions in vivo, and that the trisaccharide GlcNAcbeta,3Manbeta,4GlcbetaCer is sufficient to avoid the major phenotypic consequences associated with the GSL biosynthetic defects in Brainiac or Egghead.
Lin, Y-R, Reddy BVVG, Irvine KD.  2008.  Requirement for a core 1 galactosyltransferase in the Drosophila nervous system. Developmental dynamics : an official publication of the American Association of Anatomists. 237:3703-14. AbstractWebsite
Mucin type O-glycosylation is a widespread modification of eukaryotic proteins, but its functional requirements remain incompletely understood. It is initiated by the attachment of N-acetylgalactosamine (GalNAc) to Ser or Thr residues, and then elongated by additional sugars. We have examined requirements for mucin-type glycosylation in Drosophila by characterizing the expression and phenotypes of core 1 galactosyltransferases (core 1 GalTs), which elongate O-GalNAc by adding galactose in a beta1,3 linkage. Drosophila encode several putative core 1 GalTs, each expressed in distinct patterns. CG9520 (C1GalTA) is expressed in the amnioserosa and central nervous system. A null mutation in C1GalTA is lethal, and mutant animals exhibit a striking morphogenetic defect in which the ventral nerve cord is greatly elongated and the brain hemispheres are misshapen. Lectin staining and blotting experiments confirmed that C1GalTA contributes to the synthesis of Gal-beta1,3-GalNAc in vivo. Our results identify a role for mucin-type O-glycosylation during neural development in Drosophila.
Rogulja, D, Rauskolb C, Irvine KD.  2008.  Morphogen control of wing growth through the Fat signaling pathway. Developmental Cell. 15:309-21. AbstractWebsite
Organ growth is influenced by organ patterning, but the molecular mechanisms that link patterning to growth have remained unclear. We show that the Dpp morphogen gradient in the Drosophila wing influences growth by modulating the activity of the Fat signaling pathway. Dpp signaling regulates the expression and localization of Fat pathway components, and Fat signaling through Dachs is required for the effect of the Dpp gradient on cell proliferation. Juxtaposition of cells that express different levels of the Fat pathway regulators four-jointed and dachsous stimulates expression of Fat/Hippo pathway target genes and cell proliferation, consistent with the hypothesis that the graded expression of these genes contributes to wing growth. Moreover, uniform expression of four-jointed and dachsous in the wing inhibits cell proliferation. These observations identify Fat as a signaling pathway that links the morphogen-mediated establishment of gradients of positional values across developing organs to the regulation of organ growth.