ABSTRACT
Xenopus laevis larvae can regenerate an exact replica of the missing part of a limb after amputation at an early limb bud stage. However, this regenerative capacity gradually decreases during metamorphosis, and a froglet is only able to regenerate hypomorphic cartilage, resulting in a spike-like structure (spike). It has been reported that the spike has tissue deformities, e.g., a muscleless structure. However, our previous study demonstrated that the muscleless feature of the spike can be improved. The existence of other kinds of tissue, such as tendon, has not been clarified. In this study, we focused on the tendon and dermis, and we isolated the scleraxis and dermo-1 genes, which are known to be marker genes for the tendon and dermis, respectively. The expressions of these genes were investigated in both the developmental and regenerating processes of a Xenopus limb. Although muscle was needed to maintain scleraxis expression, scleraxis transcription was detectable in the muscleless spike. Additionally, although grafting of matured skin, including dermal tissue, inhibited limb regeneration, the expression of dermo-1, a dermal marker gene, was detected from the early stage of the froglet blastema. These results indicate that tendon precursor cells and dermal cells exist in the regenerating froglet blastema. Our results support the idea that spike formation in postmetamorphic Xenopus limbs is epimorphic regeneration.
Subject(s)
Extremities/physiology , Regeneration , Xenopus Proteins/genetics , Xenopus laevis/genetics , Xenopus laevis/physiology , Amino Acid Sequence , Animals , Avian Proteins/genetics , Basic Helix-Loop-Helix Transcription Factors/genetics , Biomarkers/analysis , Cloning, Molecular , Dermis/cytology , Gene Expression Regulation , Helix-Loop-Helix Motifs , In Situ Hybridization , Molecular Sequence Data , Phylogeny , RNA, Messenger/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid , Tendons/cytology , Transcription, Genetic , Twist-Related Protein 1 , Xenopus Proteins/chemistry , Xenopus Proteins/metabolismABSTRACT
Limb regeneration in amphibians is a representative process of epimorphosis. This type of organ regeneration, in which a mass of undifferentiated cells referred to as the "blastema" proliferate to restore the lost part of the amputated organ, is distinct from morphallaxis as observed, for instance, in Hydra, in which rearrangement of pre-existing cells and tissues mainly contribute to regeneration. In contrast to complete limb regeneration in urodele amphibians, limb regeneration in Xenopus, an anuran amphibian, is restricted. In this review of some aspects regarding adult limb regeneration in Xenopus laevis, we suggest that limb regeneration in adult Xenopus, which is pattern/tissue deficient, also represents epimorphosis.
