The Digits of the Lizard Podarcis muralis Heal But Do Not Regenerate After Topical Application of Hyaluronate and FGFs

Abstract

Attempts to stimulate blastema formation and growth of digits in lizards have been carried out by topic treatments of a hyaluronate gel embedded with FGF1-2 on the amputated surface of digits. Six to ten topic coatings were applied on the stump surface during wound healing and after re-epithelialization, from 2 hours to 20 days post-amputation. Four lizards received injection of 5BrdU to evaluate cell proliferation. Histology of controls and treated digit stumps showed that a multilayered wound epidermis formed around 10-12 days post-amputation. Connective cells present underneath the wound epidermis gave rise to fibrocytes and numerous collagen fibrils after the second week post-amputation, turning the initial soft outgrowths of 0.3-0.5 mm into a solid and scaling scar at 32 days post-injury. Injection of 5BrdU revealed that cell proliferation was low in untreated and treated digit stumps at 12 and 32 days post-amputation, explaining the lack of growth of the initial digit outgrowth. The lack of regeneration may derive from limited penetration of hyaluronate-FGF. Cells activated on the stump surface are prevalently osteogenic, blocking digit regeneration. Next subcutaneous microinjections of hyaluronate-FGF gels might obtain a better stimulatory effect and induce formation of a growing digit outgrowth, as previously obtained for the limb.