UC Irvine

Salamanders are unique among adult vertebrates in their ability to regenerate complex body structures after traumatic injury. Axolotl limb regeneration is a stepwise sequence of three requisite processes: (1) scarless wound healing to generate a regenerative wound epithelium, (2) blastema formation by migration, proliferation and dedifferentiation to create a mass of multipotent regeneration-competent progenitor cells, and (3) induction of pattern formation by interaction of cells with opposing positional information. The challenge to understanding how to induce and enhance regenerative ability in humans is to discover which of these processes fail in humans and why they fail.

In axolotl regeneration, cells maintain a memory of their original position and use this `positional information' to accurately regenerate the lost pattern. The goal of this project was to elucidate the molecular mechanism of positional information in axolotl limb regeneration and determine if it is conserved in mammals.

I used an in vivo gain-of-function assay for the requisite processes of axolotl limb regeneration (Accessory Limb Model) to determine the minimal components required to mediate positional information and induce de novo limb pattern.

I found that cell-free anterior and posterior extracellular matrix (ECM) have position-specific signaling properties that either inhibit regeneration or induce de novo limb pattern. The position-specific functionality of the ECM is established by differential expression of heparan sulfate sulfotransferases during regeneration resulting in position-specific growth factor regulation. My findings indicate that heparan sulfates are both necessary and sufficient to mediate positional information in axolotl limb regeneration. Similarly, mouse ECM was also capable of inducing limb pattern in a position-specific, heparan sulfate-dependent, age-dependent manner. Using mammalian-derived, commercially available factors, I synthetically induced axolotl limb regeneration, thus demonstrating that the factors required for regeneration are not salamander-specific.

This study demonstrates a specific novel mechanism for positional information in axolotl limb regeneration and establishes a crucial functional link between salamander regeneration and mammals. The ability to regulate axolotl regeneration with mammalian ECM has allowed identification of target mechanisms to induce regeneration in humans. In addition to the fields of regeneration, development, and glycobiology, this novel mechanism of positional information has implications to the fields of cancer biology and aging.