Regenerating limbs of urodele amphibians and Xenopus tadpole are reconstructed along proximal-distal, anterior-posterior (AP), and dorsal-ventral axes. In contrast, a regenerated limb of the Xenopus froglet does not have digits, and only a simple cartilaginous structure referred to as a "spike" is formed. This suggests that repatterning along the AP axis is absent in the froglet blastema. Previous studies have shown that Shh and its target genes are not expressed in the froglet blastema. In this study, we activated Hedgehog signaling in the froglet blastema and found that target genes of Shh were inducible in the mesenchyme of limb blastema. Furthermore, we found that activation of the signaling had effects on blastema cell proliferation and chondrogenesis and resulted in the formation of multiple cartilaginous structures. These findings indicate that activation of signaling that is absent in the froglet blastema is effective for improvement of limb regeneration ability in the Xenopus froglet.
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