JFMK, Vol. 2, Pages 25: FGFs Treatment on Amputated Lizard Limbs Stimulate the Regeneration of Long Bones, Opening New Avenues for Limb Regeneration in Amniotes: A Morphological Study

JFMK, Vol. 2, Pages 25: FGFs Treatment on Amputated Lizard Limbs Stimulate the Regeneration of Long Bones, Opening New Avenues for Limb Regeneration in Amniotes: A Morphological Study

Journal of Functional Morphology and Kinesiology doi: 10.3390/jfmk2030025

Authors: Lorenzo Alibardi

Previous studies indicated that Fibroblast Growth Factors (FGFs) are present during tail and early limb regeneration in lizards, but FGFs disappear in the limb that turns into a scar and does not regenerate at 25–40 days post-amputation. Based on these indications, the aim of the present study was to evaluate the influence of administered FGFs on limb regeneration in lizards by injections of FGF1–2 into amputated hind-limbs that were studied between 40 and 70 days post-amputation. Outgrowths of 2.0 to 3.5 mm were produced but they did not develop an autopodium during this period. The skin remained most un-scaled, resembling that of a tail blastema. Four hours before sacrifice, the animals were injected with 5BrdU to study cell proliferation using microscopic and immunofluorescent methods. Histological examination of the outgrowths at 40–70 days of regeneration showed the presence a rod of cartilage (femur), or partially or completely sub-divided into two parts likely corresponding to a tibia and fibula. The regenerated cartilage was in continuity with the transected long bones and was surrounded by a perichondrium and a dense connective tissue, sparse nerves while muscles were reduced or absent. Qualitative observations on 5BrdU-immunolabeling indicated that most proliferating cells were present in the apical wound epidermis, the apical-most perichondrium and in the regenerating scales at 40–60 days post-amputation, but decreased at 70 days. Few 5BrdU-labeled cells were seen in other tissues, including in the regenerated cartilages. The present study indicates that FGF1-2 treatment in lizards mainly stimulate cartilage regeneration and the formation of a thick epidermis with an Apical Epidermal Peg, the epidermal micro-region that favors regeneration. In summary, these results suggest that FGFs treatments on amputated limbs could also be attempted in others amniotes, including mammals. However FGFs are not capable to induce an autopodium, which requires further signaling factors for its formation.

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