The Role of Retinoic Acid in the Early Phase of Salamander Limb Regeneration

Won-Sun Kim

Sogang Univ., Dept. Life Science, Seoul, Korea

Some of the unique features in the regenerating salamander limb are the formation of the well-developed wound epidermis and the active profile of dedifferentiation in the early phase of regeneration. However, it is still not well known what the key signaling molecules are in these processes. Recently, we evaluate the role of retinoic acid, RA, as a signaling molecule or an initiator of the early events of regeneration via blocking RA synthesis using disulphiram, an inhibitor of retinaldehyde dehydrogenase that oxidizes retinal to RA. Disulphiram treatment inhibited the wound epidermis formation and dedifferentiation in the regenerating salamander limb. As a consequence, the regeneration has been delayed quite a long period of time. These inhibitory effects were noticeable when the disulphiram was administered before the formation of the wound epidermis and the onset of dedifferentiation, indicating that RA is a crucial molecule for the early events of regeneration. When RA was administered after the disulphiram treatment, the disulphiram effect could be relived. It suggests that the experimental outcome is most likely resulted from the blockade of RA synthesis and not from the side effect of the disulphiram. On the other hand, the disulphiram treatment after the dedifferentiation stage resulted in the mild retardation of regeneration. It implies that RA is also involved in the blastema growth that might be still under the influence of the wound epidermis. The gene expression of the dedifferentiation specific marker enzymes, MMP-9 and cathepsin D, was also shown to be inhibited by disulphiram. The result indicates that RA mediates dedifferentiation by regulating the expression of molecules responsible for the modification of intracellular and extracellular environment.