BackgroundEpimorphic regeneration results in the restoration of lost tissues and structures from an aggregation of proliferating cells known as a blastema. Among amniotes the most striking example of epimorphic regeneration comes from tail regenerating lizards. Although tail regeneration is often studied in the context of ecological costs and benefits, details of the sequence of tissue-level events are lacking. Here we investigate the anatomical and histological events that characterize tail regeneration in the leopard gecko, Eublepharis macularius.ResultsTail structure and tissue composition were examined at multiple days following tail loss, revealing a conserved pattern of regeneration. Removal of the tail results in a consistent series of morphological and histological events. Tail loss is followed by a latent period of wound healing with no visible signs of regenerative outgrowth. During this latent period basal cells of the epidermis proliferate and gradually cover the wound. An additional aggregation of proliferating cells accumulates adjacent to the distal tip of the severed spinal cord marking the first appearance of the blastema. Continued growth of the blastema is matched by the initiation of angiogenesis, followed by the re-development of peripheral axons and the ependymal tube of the spinal cord. Skeletal tissue differentiation, corresponding with the expression of Sox9, and muscle re-development are delayed until tail outgrowth is well underway.ConclusionsWe demonstrate that tail regeneration in lizards involves a highly conserved sequence of events permitting the establishment of a staging table. We show that tail loss is followed by a latent period of scar-free healing of the wound site, and that regeneration is blastema-mediated. We conclude that the major events of epimorphic regeneration are highly conserved across vertebrates and that a comparative approach is an invaluable biomedical tool for ongoing regenerative research.

Many lizards are able to voluntarily self‐detach (autotomize) a portion of the tail and then regenerate a functional replacement. Autotomy occurs at an intravertebral fracture plane and ruptures all the major tissue types of the tail, resulting in an open wound with various tissues exposed. The objectives of this study were to investigate the anatomy and histology of tail loss and wound healing in the leopard gecko, Eublepharis macularius. Microcomputed tomography and serial histology reveals the structure of the fracture plane and associated tissues, including a persistent notochord and sphincter muscles of the caudal artery. Following tail loss the remaining skin collapses over the wound site, the spinal cord is retracted into the original tail stump, and a clot is formed. Epithelial cells adjacent to the wound site begin to proliferate and migrate deep to the clot. Once the wound epithelium completely spans the wound site the clot drops off to reveal the developing blastema. Unlike most invasive wounds, fibrous scar tissue is not formed. Ongoing studies of wound healing studies in Eublepharis provide an important complement for ongoing regenerative research by expanding the comparative framework.

Epimorphic regeneration involves cell proliferation and the formation of a regeneration blastema to replace lost or damaged tissues. Although well described for teleosts and urodeles, this type of regeneration is also characteristic of many lizards. The objective of this study was to investigate the events that characterize epimorphic tail regeneration in the leopard gecko, Eublepharis macularius using both histochemistry and immunohistochemistry. Changes in tissue structure and composition of the regenerating tail were examined at various times post‐tail loss. A phase of wound healing follows immediately after tail loss during which time basal cells of the epidermis proliferate and migrate across the wound site. Once the wound is capped proliferation begins deep to the wound epithelium, giving rise to a localized mass of undifferentiated cells, the regeneration blastema. Blastema formation coincides with the onset of angiogenesis and redevelopment of axons and the ependymal tube of the spinal cord. Skeletal tissues differentiate somewhat later during tail regeneration, matching with the expression of Sox9. We also observe Sox9 expression in both mesenchymal and ependymal cells. Our findings demonstrate the utility of lizard tails as a model system for ongoing studies of epimorphic regeneration.Grant Funding Source: NSERC