title: Different requirement for Wnt/β-catenin signaling in limb regeneration of larval and adult Xenopus.
abstract: BACKGROUND
  In limb regeneration of amphibians, the early steps leading to blastema formation are critical for the success of regeneration, and the initiation of regeneration in an adult limb requires the presence of nerves. Xenopus laevis tadpoles can completely regenerate an amputated limb at the early limb bud stage, and the metamorphosed young adult also regenerates a limb by a nerve-dependent process that results in a spike-like structure. Blockage of Wnt/β-catenin signaling inhibits the initiation of tadpole limb regeneration, but it remains unclear whether limb regeneration in young adults also requires Wnt/β-catenin signaling.
  
  
  RESULTS
  We expressed heat-shock-inducible (hs) Dkk1, a Wnt antagonist, in transgenic Xenopus to block Wnt/β-catenin signaling during forelimb regeneration in young adults. hsDkk1 did not inhibit limb regeneration in any of the young adult frogs, though it suppressed Wnt-dependent expression of genes (fgf-8 and cyclin D1). When nerve supply to the limbs was partially removed, however, hsDkk1 expression blocked limb regeneration in young adult frogs. Conversely, activation of Wnt/β-catenin signaling by a GSK-3 inhibitor rescued failure of limb-spike regeneration in young adult frogs after total removal of nerve supply.
  
  
  CONCLUSIONS
  In contrast to its essential role in tadpole limb regeneration, our results suggest that Wnt/β-catenin signaling is not absolutely essential for limb regeneration in young adults. The different requirement for Wnt/β-catenin signaling in tadpoles and young adults appears to be due to the projection of nerve axons into the limb field. Our observations suggest that nerve-derived signals and Wnt/β-catenin signaling have redundant roles in the initiation of limb regeneration. Our results demonstrate for the first time the different mechanisms of limb regeneration initiation in limb buds (tadpoles) and developed limbs (young adults) with reference to nerve-derived signals and Wnt/β-catenin signaling.
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai, Japan. yokoyoko@biology.tohoku.ac.jp
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yokoyama
authors.forename: Tamae
authors.initials: T
authors.lastname: Maruoka
authors.forename: Haruki
authors.initials: H
authors.lastname: Ochi
authors.forename: Akio
authors.initials: A
authors.lastname: Aruga
authors.forename: Shiro
authors.initials: S
authors.lastname: Ohgo
authors.forename: Hajime
authors.initials: H
authors.lastname: Ogino
authors.forename: Koji
authors.initials: K
authors.lastname: Tamura
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D015153:Blotting, Western; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D005121:Extremities / Q000294:innervation / Q000502:physiology*; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000254:growth & development* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D012038:Regeneration / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D060509:Wnt3A Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000254:growth & development* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; C555506:WNT3A protein, Xenopus; D060509:Wnt3A Protein; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; C110182:dkk1 protein, Xenopus; C517774:fgf8a protein, zebrafish; D019938:Cyclin D1; D005346:Fibroblast Growth Factors; D038362:Glycogen Synthase Kinase 3