Dataset Information

Different requirement for Wnt/?-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/?-catenin signaling inhibits the initiation of tadpole limb regeneration, but it remains unclear whether limb regeneration in young adults also requires Wnt/?-catenin signaling.

Methodology/principal findings

We expressed heat-shock-inducible (hs) Dkk1, a Wnt antagonist, in transgenic Xenopus to block Wnt/?-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/?-catenin signaling by a GSK-3 inhibitor rescued failure of limb-spike regeneration in young adult frogs after total removal of nerve supply.

Conclusions/significance

In contrast to its essential role in tadpole limb regeneration, our results suggest that Wnt/?-catenin signaling is not absolutely essential for limb regeneration in young adults. The different requirement for Wnt/?-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/?-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/?-catenin signaling.

SUBMITTER: Yokoyama H

PROVIDER: S-EPMC3144201 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Publications

Different requirement for Wnt/β-catenin signaling in limb regeneration of larval and adult Xenopus.

Yokoyama Hitoshi H Maruoka Tamae T Ochi Haruki H Aruga Akio A Ohgo Shiro S Ogino Hajime H Tamura Koji K

PloS one 20110726 7

<h4>Background</h4>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 ...[more]

PMID: 21814549

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Project description:The frog, Xenopus laevis, possesses a high capacity to regenerate various larval tissues, including the lens, which is capable of complete regeneration from the cornea epithelium. However, the molecular signaling mechanisms of cornea-lens regeneration are not fully understood. Previous work has implicated the involvement of the Wnt signaling pathway, but molecular studies have been very limited. Iris-derived lens regeneration in the newt (Wolffian lens regeneration) has shown a necessity for active Wnt signaling in order to regenerate a new lens. Here we provide evidence that the Wnt signaling pathway plays a different role in the context of cornea-lens regeneration in Xenopus. We examined the expression of frizzled receptors and wnt ligands in the frog cornea epithelium. Numerous frizzled receptors (fzd1, fzd2, fzd3, fzd4, fzd6, fzd7, fzd8, and fzd10) and wnt ligands (wnt2b.a, wnt3a, wnt4, wnt5a, wnt5b, wnt6, wnt7b, wnt10a, wnt11, and wnt11b) are expressed in the cornea epithelium, demonstrating that this tissue is transcribing many of the ligands and receptors of the Wnt signaling pathway. When compared to flank epithelium, which is lens regeneration incompetent, only wnt11 and wnt11b are different (present only in the cornea epithelium), identifying them as potential regulators of cornea-lens regeneration. To detect changes in canonical Wnt/?-catenin signaling occurring within the cornea epithelium, axin2 expression was measured over the course of regeneration. axin2 is a well-established reporter of active Wnt/?-catenin signaling, and its expression shows a significant decrease at 24 h post-lentectomy. This decrease recovers to normal endogenous levels by 48 h. To test whether this signaling decrease was necessary for lens regeneration to occur, regenerating eyes were treated with either 6-bromoindirubin-3'-oxime (BIO) or 1-azakenpaullone - both activators of Wnt signaling - resulting in a significant reduction in the percentage of cases with successful regeneration. In contrast, inhibition of Wnt signaling using either the small molecule IWR-1, treatment with recombinant human Dickkopf-1 (rhDKK1) protein, or transgenic expression of Xenopus DKK1, did not significantly affect the percentage of successful regeneration. Together, these results suggest a model where Wnt/?-catenin signaling is active in the cornea epithelium and needs to be suppressed during early lens regeneration in order for these cornea cells to give rise to a new lentoid. While this finding differs from what has been described in the newt, it closely resembles the role of Wnt signaling during the initial formation of the lens placode from the surface ectoderm during early embryogenesis.