A1 - Niehrs / Cruciat

Wnt/β-catenin signaling plays an important role in neural development at different stages and the pathway is regulated at various levels intra- and extracellularly. To identify additional Wnt regulators we have carried out genome-wide siRNA screens and identified a novel transmembrane regulator, TMR1. In loss-of-function Wnt reporter assays, siRNA targeting TMR1 inhibits Wnt3a-induced Wnt/β-catenin signaling. In gain-of-function Wnt reporter assays, TMR1 cooperates with Wnt3a to activate Wnt/β-catenin signaling. Analysis of its embryonic expression pattern in Xenopus shows that TMR1 is expressed in the central nervous system (CNS). Consistent with a role in Wnt/β-catenin signaling in vivo, in Xenopus embryos, TMR1 synergizes with Wnt3a in axis duplication assays. Morpholino-mediated knockdown of TMR1 in Xenopus embryos leads to malformations characterized by small head and short tail, as well as loss of otx2 expression, indicating a requirement of TMR1 for CNS development. These results therefore suggest that TMR1 is a novel Wnt regulator functioning during Xenopus early CNS development. We therefore propose in two subprojects to i) analyze the role of TMR1 concerning growth and patterning of the CNS in Xenopus embryos, and to ii) elucidate its mechanism of action within the Wnt/β-catenin signaling pathway by biochemical and cell biological analysis.

Der Wnt/β-catenin Signaltransduktionsweg spielt eine wichtige Rolle in verschiedenen Stadien der neuronalen Entwicklung und wird auf unterschiedlichen Ebenen intra- und extrazellulär reguliert. Um weitere Wnt Regulatoren zu identifizieren, haben wir genomweite siRNA Screens durchgeführt und einen neuen Transmembranregulator, TMR1, identifiziert. In Wnt reporter Assays führt die Runterregulation von TMR1 mittels siRNA zur Inhibition des Wnt3a-induzierten Wnt/β-catenin Signaltransduktionswegs. Andererseits führt die Überexpression von TMR1 in Wnt reporter Assays zu einer Kooperation mit Wnt3a bezüglich der Aktivierung des Wnt/β-catenin Signaltransduktionswegs. Die Analyse seines embryonalen Expressionsmusters in Xenopus zeigt, dass TMR1 im ZNS exprimiert ist. In Übereinstimmung mit seiner Rolle im Wnt/ β-catenin Signaltransduktionsweg in vivo, kooperiert TMR1 mit Wnt3a im Körperachsen-Verdopplungsassay in Xenopus Embryos. Die Inaktivierung von TMR1 in Xenopus Embryos mittels Morpholino führt zu Fehlbildungen des Kopfes sowie zur Verminderung der otx2 Expression. Diese Ergebnisse deuten daraufhin, dass TMR1 ein neuer Wnt Regulator ist, der während der frühen XenopusXenopus Embryos und ii) die Aufklärung seines Wirkungsmechanismus im Wnt/β-catenin Signaltransduktionsweg mittels biochemischer und zellbiologischer Methoden. ZNS Entwicklung benötigt wird. Zur weiteren Charakterisierung schlagen wir die folgenden 2 Teilprojekte vor: i) die Analyse der Rolle von TMR1 in der Entwicklung und Musterbildung des ZNS in

Own project-related publications since the last application

Davidson, G., Wu, W., Shen, J., Bilic, J., Fenger, U., Stannek, P., Glinka, A., and Niehrs, C. (2005) Casein kinase 1 gamma couples Wnt receptor activation to cytoplasmic signal transduction. Nature 438: 867-872

Cruciat, C.M., Hassler, C., and Niehrs, C. (2006) The MRH protein Erlectin is a member of the endoplasmic reticulum synexpression group and functions in N-glycan recognition. J Biol Chem 281: 12986-12993

Bilic, J., Huang, Y.L., Davidson, G., Zimmermann, T., Cruciat, C.M., Bienz, M., and Niehrs, C. (2007) Wnt induces LRP6 signalosomes and promotes dishevelled-dependent LRP6 phosphorylation. Science 316: 1619-1622

Hassler, C., Cruciat, C.M., Huang, Y.L., Kuriyama, S., Mayor, R., and Niehrs, C. (2007) Kremen is required for neural crest induction in Xenopus and promotes LRP6-mediated Wnt signaling. Development 134: 4255-4263

Reviews

Niehrs, C. (2005) Axis formation: redundancy rules. Curr Biol 15: R391-393

Niehrs, C. (2006) Function and biological roles of the Dickkopf family of Wnt modulators. Oncogene 25: 7469-7481

*Own project-related publications prior to 2005

Mao, B., Wu, W., Davidson, G., Marhold, J., Li, M., Mechler, B., Delius, H., Hoppe, D., Stannek, P., Walter, C., Glinka, A. and Niehrs, C. (2002) Kremens are novel Dickkopf receptors that regulate Wnt/beta-catenin signalling. Nature 417: 664-667

Mao, B., and Niehrs, C. (2003) Kremen2 modulates Dickkopf2 activity during Wnt/LRP6 signaling. Gene 302: 179-183

Del Barco Barrantes, I., Davidson, G., Gröne, H.J., Westphal, H., and Niehrs, C. (2003) Dkk1 and noggin cooperate in mammalian head induction. Genes Dev 17: 2239-2344

Kazanskaya, O., Glinka, A., Del Barco Barrantes, I., Stannek, P., Niehrs, C., and Wu, W. (2004) R-Spondin2 Is a Secreted Activator of Wnt/beta-Catenin Signaling and Is Required for Xenopus Myogenesis. Dev Cell 7: 525-534

Selected publications from other projects outside the SFB since 2005

Baldessari, D., Shin, Y., Krebs, O., Konig, R., Koide, T., Vinayagam, A., Fenger, U., Mochii, M., Terasaka, C., Kitayama, A., et al. and Niehrs, C. (2005) Global gene expression profiling and cluster analysis in Xenopus laevis. Mech Dev 122: 441-475

Pollet, N., Muncke, N., Verbeek, B., Li, Y., Fenger, U., Delius, H., and Niehrs, C. (2005) An atlas of differential gene expression during early Xenopus embryogenesis. Mech Dev 122: 365-439

Karaulanov, E.E., Bottcher, R.T., and Niehrs, C. (2006) A role for fibronectin-leucine-rich transmembrane cell-surface proteins in homotypic cell adhesion. EMBO Rep 7: 283-290

Barreto, G., Schafer, A., Marhold, J., Stach, D., Swaminathan, S.K., Handa, V., Doderlein, G., Maltry, N., Wu, W., Lyko, F. and Niehrs, C. (2007) Gadd45a promotes epigenetic gene activation by repair-mediated DNA demethylation. Nature 445: 671-675

Pinho, S., and Niehrs, C. (2007) Dkk3 is required for TGF-beta signaling during Xenopus mesoderm induction. Differentiation 75: 957-967

Christof Niehrs

Abteilung für Molekulare Embryologie
DKFZ
Im Neuenheimer Fald 581
69120 Heidelberg

Phone: 06221-424690
Fax:     06221-424692
niehrs(at)dkfz-heidelberg.de

Cristina-Maria Sirrenberg-Cruciat

DKFZ
Im Neuenheimer Fald 581
69120 Heidelberg

Phone: 06221-424691
Fax:     06221-424692
c.cruciat(at)dkfz-heidelberg.de