Abstract
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.
Highlights
The loss of limbs in amniotes, if not immediately fatal due to extensive bleeding, results in a permanent deficit since the limb cannot regenerate, a condition that in nature leads more or less rapidly to death
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
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
Summary
The loss of limbs in amniotes, if not immediately fatal due to extensive bleeding, results in a permanent deficit since the limb cannot regenerate, a condition that in nature leads more or less rapidly to death. The recovery from limb loss in lizards, generally results in the formation of a flat scar of 0.5–1.0 mm that rapidly becomes scaled. The time elapsed for the formation of these rare long tail-like outgrowths is generally unknown, aside for the wall lizard Podarcis muralis where 3–12 months were recoded [3,6]. Sicula and P. muralis [4] showed a rapid, but limited growth, of 2–3 mm in rare cases within 2 months post-amputation. In the snake-eyed skink, indicatively 2–4 mm of limb outgrowths were formed at 106 and 203 days post-amputation [9]
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