Epimorphic vs. tissue regeneration in Xenopus forelimbs

Abstract

Postmetamorphic froglets of Xenopus laevis regenerate hypomorphic unbranched spikes from amputated arm stumps. These are composed primarily of cartilage, produced from blastemalike structures sparsely populated with cells and rich in connective tissue. Some consider these outgrowths to be an example of epimorphic regeneration produced from blastemas, albeit deficient ones. Others interpret them as a case of tissue regeneration derived from fibroblastemas augmented by chondrocytes and periosteal and perichondrial fibroblasts. To resolve these alternatives, forelimbs were amputated proximal to the wrist, skinned, and inserted through the body wall into the abdominal cavity. In the absence of skin, epidermal wound healing failed to occur and blastemas could not develop. After 2 months, by which time controls had regenerated spikes averaging 3.38 mm long, the denuded stumps had not given rise to outgrowths. They typically developed cartilaginous caps on the severed ends of the radius-ulna, and in rare cases formed amorphous growths of cartilage. If blastema formation is considered diagnostic of epimorphic regeneration and tissue regeneration can proceed in the absence of epidermal wound healing and blastema formation, these findings lead to the conclusion that Xenopus limb regeneration is epimorphic.

Deer antler regeneration: Cells, concepts, and controversies

“…However, other regeneration biologists (Carlson, 1978(Carlson, , 2005Goss, 1980Goss, , 1983Goss, , 1984Reichman, 1984;Goss and Holt, 1992) do not use the term epimorphic regeneration in this broad sense, but apply a narrower (more specific) concept of this process. For these authors, epimorphic regeneration by definition involves the formation of a blastema composed of dedifferentiated cells.…”

Beyond early development: Xenopus as an emerging model for the study of regenerative mechanisms

“…This contrasts with the situation in urodeles where a complete and correctly patterned limb is regrown: the textbook case of epimorphic regeneration (see Box 1 for definition). Grafting experiments performed by Goss and Holt in 1992 support the idea that epithelial-mesenchymal interactions are required for production of the hypomorphic spike (Goss and Holt, 1992). They showed that skinned forelimbs amputated at wrist level could not form a blastema when inserted into the abdominal cavity.…”

Cellular and molecular mechanisms of regeneration inXenopus

“…Indeed the mosaic behaviour of the chick limb bud was long held to represent evidence for the progress zone model (Summerbell et al 1973). However, like other anurans, and unlike urodele amphibians, Xenopus can produce only the occasional hypomorphic unbranched spike if amputated after metamorphosis (Goss & Holt 1992 One hundred per cent of complete regenerates can only be formed up to stage 52, when the developing limb is a flattened paddle shape, and the ability to regenerate a complete limb declines progressively until stage 57 when only the occasional toe is formed (Dent 1962). Although this ability is of some interest, it is not clear, prima facie, that it is really the same sort of phenomenon as regeneration of the urodele limb, which involves dedifferentiation of mature cells to form a blastema (Nye et al 2003).…”