No description available.

No description available.

No description available.

No description available.

Les cils et flagelles sont des organites cellulaires retrouvés des protozoaires aux mammifères. Une dérégulation de l’assemblage (ciliogenèse) ou de la fonction des cils, entraîne diverses maladies chez l’homme. Parmi les acteurs de la ciliogenèse, se trouvent les facteurs de transcription RFX. La recherche de gènes cibles de RFX chez la drosophile a permis d’identifier le gène Chibby (Cby), précédemment décrit comme un antagoniste de la voie de signalisation Wnt/wingless. Contrairement aux vertébrés, chez les invertébrés aucun lien n’est encore établi entre cil et voie wg. L’identification de cby comme cible de dRFX chez la drosophile suggère une fonction ciliaire de cby et permettrait l’établissement du lien cil/voie wg. CBY se localise à la zone de transition des cils des neurones sensoriels du système nerveux périphérique et aux centrioles des spermatides. Les drosophiles invalidées pour cby présentent un phénotype de non coordination, mais aucun phénotype de type wg. Ces mutants ont des défauts des cils sensoriels, ainsi que des défauts d’organisation des spermatides. De plus, chez les embryons, les protéines actrices du transport intra-flagellaire, NompB et CG11356, sont mal distribuées lorsque CBY est absente. Enfin, chez les mutants, la localisation de la protéine UNC est affectée dans les cellules germinales en fin de spermatogenèse. En conclusion, chez la drosophile, CBY est impliquée dans le tri protéique organisé à la base du cil de neurones sensoriels, de concert avec les autres protéines localisées à la zone de transition. Dans le testicule, CBY est nécessaire à la maturation des spermatides. En revanche, CBY n‟intervient pas dans la régulation de la voie wg / Cilia and flagella are organelles found from protozoa to mammals. Deregulation of the assembly (ciliogenesis) or function of cilia, causes various diseases in humans. Among those involved in ciliogenesis are the RFX transcription factors. The search for RFX target genes in Drosophila identified the Chibby (CBY) gene, previously described as an antagonist of the Wnt / wingless pathway. Unlike in vertebrates, in invertebrates is still no link established between cilia and the wg pathway. The identification of CBY as a target of dRFX in Drosophila suggests a ciliary function of CBY and would allow the establishment of the link cilia / wg pathway. CBY is localized at the transition zone of cilia of sensory neurons of the peripheral nervous system and at centrioles in spermatids. Drosophila invalidated for CBY present a phenotype of uncoordination, but no wg phenotype. These mutants have defects in sensory cilia and defects in organization of spermatids. In addition, in embryos, the distribution of proteins involved in intra-flagellar transport, NompB and CG11356, is affected when CBY is absent. Finally, in the mutants, the localization of the UNC protein is affected in germ cells at the end of spermatogenesis. In conclusion, in Drosophila, CBY is involved in the protein sorting organized at the base of cilia of sensory neurons, with the other proteins located at the transition zone. In the testes, CBY is necessary for the maturation of spermatids. However, CBY is not involved in the regulation of the wg pathway

No description available.

Morphogens of the Wnt and Hedgehog families are secreted signaling molecules that coordinate growth and patterning of many different tissues. Both, Wingless and Hedgehog spread across long distances in developing wing of Drosophila melanogaster. However, both proteins are covalently modified with lipid moieties. The mechanisms that allow long-range movement of such hydrophobic molecules are unclear. Like Wingles and Hedgehog, glycosylphosphatidylinositol (gpi)-linked proteins also transfer between cells with their lipid anchor intact. It has been speculated that gpi-linked proteins and lipid-linked morphogens travel together on a membranous particle, which was termed an argosome. As yet however, no functional link between argosome production and dispersal of lipid-linked proteins has been established. The topic of this thesis is to understand the cell biological nature of the argosome and thus contribute to understanding of morphogen gradient formation. To address the question of argosome biosynthesis, at least two models have been proposed. One possibility is that argosomes are membranous exovesicles with a complete membrane bilayer. Alternatively, argosomes might resemble lipoprotein particles that comprise on of a family of apolipoproteins scaffolded around a phospholipid monolayer that surrounds a core of esterified cholesterol and triglyceride. Lipid-modified proteins of the exoplasmic face of the membrane (like GFPgpi, Wingless or Hedgehog) might fit well into the outer phospholipid monolayer of such a particle. Here, I utilize biochemical fractionation to determine the sort of particle that lipid-linked proteins associate with. I show that Wingless, Hedgehog and gpi-linked proteins bind Drosophila lipoprotein particles in vitro, and colocalize with them in wing imaginal discs. Next, I use genetic means to address the functional importance of this association. I demonstrate that reducing Lipophorin levels in Drosophila larvae perturbs long-range but not shor-range Wingless and Hedgehog signaling, and increases the sequestration of Hedgehog by Patched. I propose that Lipophorin particles are vehicles for the long-range movement of lipid-linked morphogens and gpi-linked proteins.

Animal morphogenesis is largely driven by concerted changes in the shape of individual cells. However, how cell shape changes are regulated and coordinated in developing animals is not well understood. Here we show that the two perpendicular signaling gradients of the morphogens Dpp, a TGF-β homologue, and Wingless, a Wnt family member, maintain tissue homoeostasis and control cell shape changes in the developing Drosophila wing. Clones of cells lacking Dpp or Wingless signaling invaginate apically, shorten apico-basally and subsequently extrude basally without disruption of the epithelium. During early larval development, the onset of Dpp and Wingless signaling correlates with the cuboidal-to-columnar cell shape transition of wing disc cells. Gradients in apical-basal length of columnar cells correlate during late larval development with the gradients of Dpp and Wingless signaling activities. Cells receiving high levels of Dpp and Wingless signaling are most elongated and apically constricted. Low levels of Dpp and Wingless signaling correlate with a shorter and apically wider cell morphology. Dpp and Wingless signaling is cell-autonomously required for maintaining the elongated columnar cell shape of late larval wing disc cells. Overactivation of these pathways results in precocious cell elongation during early larval development. These morphogenetic responses to Dpp and Wingless require the transcription factor complexes Mad and Tcf/β-catenin, respectively, indicating that they are mediated by changes in gene expression. The morphogenetic function of Wingless is in part mediated by one of its target genes, the transcription factor Vestigial. Wingless signaling promotes an enrichment of E-cadherin at the adherens junctions, and we show that E-cadherin is required to maintain apical-basal cell length. Dpp signaling controls the subcellular distribution of the activities of the small GTPase Rho1 and the regulatory light chain of non-muscle myosin II (MRLC). Alteration of Rho1 or MRLC activity has a profound effect on apical-basal cell length. Finally, we demonstrate that a decrease in Rho1 or MRLC activity rescues the shortening of cells with compromised Dpp signaling. Our results identify cell-autonomous roles for Dpp and Wingless signaling in promoting and maintaining the elongated columnar shape of wing disc cells. Furthermore, they suggest that Dpp and Wingless signaling control cell shape by regulating the actin-MyosinII/E-cadherin network. / Morphogenese in Tieren wird in hohem Maße von konzertierten Zellformveränderungen einzelner Zellen bewirkt. Es ist jedoch noch nicht hinreichend verstanden, wie Zellformveränderungen in sich entwickelnden Tieren reguliert und koordiniert werden. Hier zeigen wir, dass die zwei zueinander senkrecht stehenden Signalgradienten der Morphogene Dpp, eines TGF-β Homologs, und Wingless, eines Mitglieds der Wnt Familie, im sich entwickelnden Drosophila-Flügel Gewebe-Homöostase aufrechterhalten und Zellformveränderungen kontrollieren. Klone von Zellen, denen Dpp oder Wingless Signalaktivität fehlt, invaginieren von ihrer apikalen Seite her, verkürzen sich in apiko-basaler Richtung und extruieren im Folgenden auf der basalen Seite des Epithels, ohne es zu zerstören. Während der frühen Larvalentwicklung korreliert das Anschalten der Dpp und Wingless Signale mit der Zellformveränderung der Flügelscheibenzellen von kuboidal zu kolumnar. Gradienten in der apiko-basalen Länge von kolumnaren Zellen korrelieren während der späten Larvalentwicklung mit den Gradienten der Dpp und Wingless Signalaktivitäten. Zellen, die hohe Werte an Dpp und Wingless Signalen empfangen, sind am meisten elongiert und apikal konstringiert. Niedrige Werte von Dpp und Wingless Signalen korrelieren mit kürzerer und apikal weiterer Zellmorphologie. Dpp und Wingless Signale werden zellautonom gebraucht für die Aufrechterhaltung der elongierten Zellform von späten larvalen Flügelscheibenzellen. Die Überaktivierung dieser Signalwege führt zu vorzeitiger Zellverlängerung während der frühen Larvalentwicklung. Diese morphogenetischen Antworten auf Dpp und Wingless benötigen die Transkriptionsfaktor-Komplexe Mad beziehungsweise Tcf/β-catenin, was darauf hindeutet, dass sie durch Änderungen in der Genexpression vermittelt werden. Die morphogenetische Funktion von Wingless wird teilweise durch eines seiner Zielgene, Vestigial, vermittelt. Wingless Signale fördern die Anreicherung von E-cadherin an den Adherensverbindungen. Wir zeigen hier, dass E-cadherin gebraucht wird, um apiko-basale Zelllänge aufrechtzuerhalten. Dpp Signale kontrollieren die subzelluläre Verteilung der Aktivitäten der kleinen GTPase Rho1 und der regulatorischen leichten Kette von nicht-muskulärem Myosin II (MRLC). Eine Änderung in der Rho1 oder MRLC Aktivität hat weitreichende Auswirkungen auf die apiko-basale Zelllänge. Schließlich zeigen wir noch, dass eine Verringerung der Rho1 oder MRLC Aktivitäten die Zellverkürzung von Dpp-Signal kompromittierten Zellen rettet. Unsere Resultate identifizieren zellautonome Rollen für Dpp und Wingless Signale in der Förderung und Aufrechterhaltung der elongierten kolumnaren Zellform von Flügelimaginalscheibenzellen. Darüber hinaus suggerieren sie, dass Dpp und Wingless Signale die Zellform durch die Regulierung des Aktin-MyosinII/E-cadherin-Netzwerks kontrollieren.

Morphogens of the Wnt and Hedgehog families are secreted signaling molecules that coordinate growth and patterning of many different tissues. Both, Wingless and Hedgehog spread across long distances in developing wing of Drosophila melanogaster. However, both proteins are covalently modified with lipid moieties. The mechanisms that allow long-range movement of such hydrophobic molecules are unclear. Like Wingles and Hedgehog, glycosylphosphatidylinositol (gpi)-linked proteins also transfer between cells with their lipid anchor intact. It has been speculated that gpi-linked proteins and lipid-linked morphogens travel together on a membranous particle, which was termed an argosome. As yet however, no functional link between argosome production and dispersal of lipid-linked proteins has been established. The topic of this thesis is to understand the cell biological nature of the argosome and thus contribute to understanding of morphogen gradient formation. To address the question of argosome biosynthesis, at least two models have been proposed. One possibility is that argosomes are membranous exovesicles with a complete membrane bilayer. Alternatively, argosomes might resemble lipoprotein particles that comprise on of a family of apolipoproteins scaffolded around a phospholipid monolayer that surrounds a core of esterified cholesterol and triglyceride. Lipid-modified proteins of the exoplasmic face of the membrane (like GFPgpi, Wingless or Hedgehog) might fit well into the outer phospholipid monolayer of such a particle. Here, I utilize biochemical fractionation to determine the sort of particle that lipid-linked proteins associate with. I show that Wingless, Hedgehog and gpi-linked proteins bind Drosophila lipoprotein particles in vitro, and colocalize with them in wing imaginal discs. Next, I use genetic means to address the functional importance of this association. I demonstrate that reducing Lipophorin levels in Drosophila larvae perturbs long-range but not shor-range Wingless and Hedgehog signaling, and increases the sequestration of Hedgehog by Patched. I propose that Lipophorin particles are vehicles for the long-range movement of lipid-linked morphogens and gpi-linked proteins.

Animal morphogenesis is largely driven by concerted changes in the shape of individual cells. However, how cell shape changes are regulated and coordinated in developing animals is not well understood. Here we show that the two perpendicular signaling gradients of the morphogens Dpp, a TGF-β homologue, and Wingless, a Wnt family member, maintain tissue homoeostasis and control cell shape changes in the developing Drosophila wing. Clones of cells lacking Dpp or Wingless signaling invaginate apically, shorten apico-basally and subsequently extrude basally without disruption of the epithelium. During early larval development, the onset of Dpp and Wingless signaling correlates with the cuboidal-to-columnar cell shape transition of wing disc cells. Gradients in apical-basal length of columnar cells correlate during late larval development with the gradients of Dpp and Wingless signaling activities. Cells receiving high levels of Dpp and Wingless signaling are most elongated and apically constricted. Low levels of Dpp and Wingless signaling correlate with a shorter and apically wider cell morphology. Dpp and Wingless signaling is cell-autonomously required for maintaining the elongated columnar cell shape of late larval wing disc cells. Overactivation of these pathways results in precocious cell elongation during early larval development. These morphogenetic responses to Dpp and Wingless require the transcription factor complexes Mad and Tcf/β-catenin, respectively, indicating that they are mediated by changes in gene expression. The morphogenetic function of Wingless is in part mediated by one of its target genes, the transcription factor Vestigial. Wingless signaling promotes an enrichment of E-cadherin at the adherens junctions, and we show that E-cadherin is required to maintain apical-basal cell length. Dpp signaling controls the subcellular distribution of the activities of the small GTPase Rho1 and the regulatory light chain of non-muscle myosin II (MRLC). Alteration of Rho1 or MRLC activity has a profound effect on apical-basal cell length. Finally, we demonstrate that a decrease in Rho1 or MRLC activity rescues the shortening of cells with compromised Dpp signaling. Our results identify cell-autonomous roles for Dpp and Wingless signaling in promoting and maintaining the elongated columnar shape of wing disc cells. Furthermore, they suggest that Dpp and Wingless signaling control cell shape by regulating the actin-MyosinII/E-cadherin network. / Morphogenese in Tieren wird in hohem Maße von konzertierten Zellformveränderungen einzelner Zellen bewirkt. Es ist jedoch noch nicht hinreichend verstanden, wie Zellformveränderungen in sich entwickelnden Tieren reguliert und koordiniert werden. Hier zeigen wir, dass die zwei zueinander senkrecht stehenden Signalgradienten der Morphogene Dpp, eines TGF-β Homologs, und Wingless, eines Mitglieds der Wnt Familie, im sich entwickelnden Drosophila-Flügel Gewebe-Homöostase aufrechterhalten und Zellformveränderungen kontrollieren. Klone von Zellen, denen Dpp oder Wingless Signalaktivität fehlt, invaginieren von ihrer apikalen Seite her, verkürzen sich in apiko-basaler Richtung und extruieren im Folgenden auf der basalen Seite des Epithels, ohne es zu zerstören. Während der frühen Larvalentwicklung korreliert das Anschalten der Dpp und Wingless Signale mit der Zellformveränderung der Flügelscheibenzellen von kuboidal zu kolumnar. Gradienten in der apiko-basalen Länge von kolumnaren Zellen korrelieren während der späten Larvalentwicklung mit den Gradienten der Dpp und Wingless Signalaktivitäten. Zellen, die hohe Werte an Dpp und Wingless Signalen empfangen, sind am meisten elongiert und apikal konstringiert. Niedrige Werte von Dpp und Wingless Signalen korrelieren mit kürzerer und apikal weiterer Zellmorphologie. Dpp und Wingless Signale werden zellautonom gebraucht für die Aufrechterhaltung der elongierten Zellform von späten larvalen Flügelscheibenzellen. Die Überaktivierung dieser Signalwege führt zu vorzeitiger Zellverlängerung während der frühen Larvalentwicklung. Diese morphogenetischen Antworten auf Dpp und Wingless benötigen die Transkriptionsfaktor-Komplexe Mad beziehungsweise Tcf/β-catenin, was darauf hindeutet, dass sie durch Änderungen in der Genexpression vermittelt werden. Die morphogenetische Funktion von Wingless wird teilweise durch eines seiner Zielgene, Vestigial, vermittelt. Wingless Signale fördern die Anreicherung von E-cadherin an den Adherensverbindungen. Wir zeigen hier, dass E-cadherin gebraucht wird, um apiko-basale Zelllänge aufrechtzuerhalten. Dpp Signale kontrollieren die subzelluläre Verteilung der Aktivitäten der kleinen GTPase Rho1 und der regulatorischen leichten Kette von nicht-muskulärem Myosin II (MRLC). Eine Änderung in der Rho1 oder MRLC Aktivität hat weitreichende Auswirkungen auf die apiko-basale Zelllänge. Schließlich zeigen wir noch, dass eine Verringerung der Rho1 oder MRLC Aktivitäten die Zellverkürzung von Dpp-Signal kompromittierten Zellen rettet. Unsere Resultate identifizieren zellautonome Rollen für Dpp und Wingless Signale in der Förderung und Aufrechterhaltung der elongierten kolumnaren Zellform von Flügelimaginalscheibenzellen. Darüber hinaus suggerieren sie, dass Dpp und Wingless Signale die Zellform durch die Regulierung des Aktin-MyosinII/E-cadherin-Netzwerks kontrollieren.