Formation of a New Limb Bud at the Boundary Between a Transplanted Limb Bud and the Tail Surface ofXenopusTadpoles

Abstract

Through transplantation experiments with Xenopus laevis tadpoles, we found a new morphogenetic phenomenon consisting of limb bud formation at the boundary between transplanted whole limb buds and the tail surface. This phenomenon occurs without limb-limb stump interaction and has a number of unique features: (1) Only one extra limb bud was formed per transplant and the new limb and the transplanted limb were bilaterally symmetrical, forming a pair of limb girdles. (2) Extra new limb bud formation occurred not only at the tail but also at other non-limb regions, including abdominal and head surfaces. (3) Successful limb formation required the presence of basal 1/4 region (presumptive limb girdle) of a limb bud explant. (4) New limb formation was host-stage-dependent: before metamorphosis, limb bud formation ratio was high (> 90%), but as the host tadpole entered metamorphosis, this potential declined and morphological abnormalities of new limbs increased. (5) Cell lineage analysis showed that epidermis of the new limb bud always contained many (about 60%) host-derived cells, while new limb cartilage cells were completely graft-derived. These results suggest that heterotopic new limb formation occurs through interaction between graft mesenchyme and host epidermis. Thus, the present study has clarified the two important aspects of limb ontogeny: the importance of presumptive limb girdle for the limb bud initiation and the relationship between limb bud formation potential and metamorphic tissue remodeling. The present experimental system may help to improve our understanding of epithelial-mesenchymal interaction during limb bud initiation and subsequent limb cell differentiation during metamorphosis.

Vitamin A induced homeotic hindlimb formation on dorsal and ventral sides of regenerating tissue of amputated tails of Japanese brown frog tadpoles

“…However, more limbs were found in some regenerates, suggesting the further induction or duplication of trunk positional values to produce limb fields. The mechanism for the formation of more than four paired limbs in a tail regenerate might be similar to the process through which the systemic administration of retinoids duplicates regenerating anuran limbs (reviewed by Maden ) or through which a new limb is induced on the base of a limb implanted on the tail in X. laevis (Adaniya & Nishikawa ).…”