R-Spondin2 is a secreted activator of Wnt/beta-catenin signaling and is required for Xenopus myogenesis.
We have carried out a small pool expression screen for modulators of the Wnt/beta-catenin pathway and identified Xenopus R-spondin2 (Rspo2) as a secreted activator of this cascade. Rspo2 is coexpressed with and positively regulated by Wnt signals and synergizes with Wnts to activate beta-catenin. Analyses of functional interaction with components of the Wnt/beta-catenin pathway suggest that Rspo2 functions extracellularly at the level of receptor ligand interaction. In addition to activating the Wnt/beta-catenin pathway, Rspo2 overexpression blocks Activin, Nodal, and BMP4 signaling in Xenopus, raising the possibility that it may negatively regulate the TGF-beta pathway. Antisense Morpholino experiments in Xenopus embryos and RNAi experiments in HeLa cells reveal that Rspo2 is required for Wnt/beta-catenin signaling. In Xenopus embryos depleted of Rspo2, the muscle markers myoD and myf5 fail to be activated and later muscle development is impaired. Thus, Rspo2 functions in a positive feedback loop to stimulate the Wnt/beta-catenin cascade.
Division of Molecular Embryology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
Olga
O
Kazanskaya
Andrei
A
Glinka
Ivan
I
del Barco Barrantes
Peter
P
Stannek
Christof
C
Niehrs
Wei
W
Wu
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D046508:Culture Techniques / Q000379:methods; D003598:Cytoskeletal Proteins; D016326:Extracellular Matrix Proteins; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins; D008156:Luciferases / Q000378:metabolism; D008845:Microinjections; D008969:Molecular Sequence Data; D024510:Muscle Development; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012313:RNA / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators; D051153:Wnt Proteins; D014981:Xenopus / Q000196:embryology* / Q000235:genetics; D029867:Xenopus Proteins / Q000737:chemistry / Q000378:metabolism*; D051176:beta Catenin
C495266:CTNNB1 protein, Xenopus; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D016326:Extracellular Matrix Proteins; D036341:Intercellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C493338:Rspo2 protein, Xenopus; C122166:SPON2 protein, human; D015534:Trans-Activators; D051153:Wnt Proteins; D029867:Xenopus Proteins; D051176:beta Catenin; D012313:RNA; D008156:Luciferases