A stepwise model system for limb regeneration

T Endo

doi:10.1016/s0012-1606(04)00135-6

Abstract

The amphibian limb is a model that has provided numerous insights into the principles and mechanisms of tissue and organ regeneration. While later stages of limb regeneration share mechanisms of growth control and patterning with limb development, the formation of a regeneration blastema is controlled by early events that are unique to regeneration. In this study, we present a stepwise experimental system based on induction of limb regeneration from skin wounds that will allow the identification and functional analysis of the molecules controlling this early, critical stage of regeneration. If a nerve is deviated to a skin wound on the side of a limb, an ectopic blastema is induced. If a piece of skin is grafted from the contralateral side of the limb to the wound site concomitantly with nerve deviation, the ectopic blastema continues to grow and forms an ectopic limb. Our analysis of dermal cell migration, contribution, and proliferation indicates that ectopic blastemas are equivalent to blastemas that form in response to limb amputation. Signals from nerves are required to induce formation of both ectopic and normal blastemas, and the diversity of positional information provided by blastema cells derived from opposite sides of the limb induces outgrowth and pattern formation. Hence, this novel and convenient stepwise model allows for the discovery of necessary and sufficient signals and conditions that control blastema formation, growth, and pattern formation during limb regeneration.

Highlights

Urodele amphibians are unique among adult vertebrates in their ability to regenerate many of their body parts
Our results show that limb regeneration can be reproducibly induced by a series of experimentally supplied signals in an ectopic location, providing a stepwise experimental system for the analysis of regeneration (Fig. 8)
The first of the signals is provided by nerves and is sufficient to turn a wound that would have regenerated only skin, into a bump, the equivalent of a regeneration blastema

Summary

Introduction

Urodele amphibians are unique among adult vertebrates in their ability to regenerate many of their body parts. The later phase of limb regeneration is equivalent to limb development, the early phase, resulting in the genesis of the blastema, is unique to regeneration. It is this phase that we seek to understand so as to be able to enhance regenerative processes in humans. Later studies demonstrated that extensive trauma was not required if a piece of skin (connective tissue fibroblasts) was grafted from the contralateral side of the limb to the wound site in conjunction with a deviated nerve (Lheureux, 1977; Maden and Holder, 1984; Reynolds et al, 1983), the frequency of full regeneration was variable. Sections were stained with either hematoxylin and eosin or Mallory’s triple stain (Humason, 1979)

Materials and methods

Surgical procedures

Results

Discussion