Regenerative capacity in Xenopus laevis tadpole tail

The ability to regenerate lost tissue and organs varies among animal species, tissue and life cycle stages and the nature of repair responses has been related to the dynamic, reciprocal interactions among several signalling molecules and the cell types present and activated at the wound site. Amphibians, and in particular Xenopus laevis, provide excellent models to examine cellular and molecular mechanisms involved in the progressive loss of regenerative potential. In this context, X. laevis tadpoles in different regenerative competence stages (st 50 and st 55) were studied after tail partial amputation. The histochemical results showed similar sequences of repair events, i.e., the epithelial wound closure, the formation of a neural ampulla and a bullet-shaped mass of cells at the cut end of the notochord surrounded by mesenchymal-like cells, but they were by means different morphological patterns. Moreover differences were in a delayed full tail reconstitution in st 56, and in the extent of inflammatory responses and angiogenesis at the wound tail stumps. Immunoreactivity to antibodies for critical healing immune mediators, such as indicible nitric oxide (NO) synthase, was also found in a greater number of cells, mainly leukocytes, from the early healing phase in older tadpoles. On the whole, our data indicate an important involvement of the immune cells and induction of NO synthesis in wound microenvironment in modulating the degree of immune responses and repair quality outcomes that may be at least partly related to the gradual decline of tail regeneration efficiency during tadpole development.