Characterization of Xenopus digits and regenerated limbs of the froglet

Abstract

Xenopus has 4 and 5 digits in a forelimb and hindlimb, respectively. It is thought that their limbs and digits develop in Xenopus by mechanisms that are almost conserved from amphibians to higher vertebrates. This is supported by some molecular evidence. The 5hoxd genes are convenient marker genes for characterizing digits in the chick and mouse. The anteriormost digit is characterized by being hoxd13-positive and hoxd12 (hoxd11)-negative in the chick and mouse. In this study, we revealed that the anteriormost digit of the Xenopus forelimb is hoxd13-positive and hoxd11-positive, that is, a more posterior character than digit I. The order of formation of digit cartilages also suggested that Xenopus forelimb digit identity is II to V, not I to IV. We have also been interested in the relationship between digit identity and shh. The anteriormost digit develops in a shh-independent way. A limb treated with cyclopamine (a shh inhibitor) has a gene expression pattern (hoxd11-negative) similar to that in shh-deficient mice, suggesting that a hindlimb treated with cyclopamine has a digit I character. However, a Xenopus froglet regenerate (spike), which lacks shh expression during its regeneration process, does not have such an expression pattern, being hoxd11-positive. We investigated hoxd11 transcriptions in blastemas that formed in the anteriormost and posteriormost digits, and we found that the blastemas have different hoxd11 expression levels. These findings suggest that the froglet limb blastema does not have a mere digit I character in spite of shh defectiveness and that the froglet limb blastema recognizes its positional differences along the anteriorposterior axis. Developmental Dynamics 235:3316 -3326, 2006.

Attenuation of bone morphogenetic protein signaling during amphibian limb development results in the generation of stage‐specific defects

“…In both shh À/À mice and our noggin-expressing tadpoles, this single hindlimb digit has two phalanges, suggestive of a digit I identity. However, analysis of hoxd11-13 expression in shh À/À mice showed loss of late-phase hoxd11 expression, further supporting the digit I identity (Chiang et al 2001) In Xenopus limbs treated with the shh inhibitor cyclopamine, the resulting single digits also showed a hoxd13 + hoxd11-phenotype, typical of digit I (Satoh et al 2006). In contrast, in our BMP-inhibited tadpoles, both hoxd11 and hoxd13 were present in the single digit, indicating a more posterior identity (Fig.…”

“…The hypodactylous limb caused by BMP attenuation in mid limb bud development therefore has a mixed identity, developing from the normal position of digit IV, with a digit IV hox code and an eventual digit I morphology. Interestingly in regenerating froglet forelimbs, in which shh signaling is not re-established, the single spike that forms is hoxd11-positive as well, indicating a posterior identity (Satoh et al 2006). Noggin beads placed interdigitally can cause anterior homeotic transformation of the digits in developing chicken hindfeet.…”

“…In X. laevis, normal developing forelimbs have four digits, numbered II-V (Satoh et al 2006;Fig. 1A), and hindlimbs have five digits, I-V, with the anterior three digits bearing claws (Fig.…”

Different Requirement for Wnt/β-Catenin Signaling in Limb Regeneration of Larval and Adult Xenopus

“…At stage 54, a forelimb bud becomes paddle-shaped, comparable to the hindlimb bud at stage 52 (Figure S1A, [39]). Regeneration of forelimb buds amputated at stage 54 was efficiently blocked in the hsDkk1 tadpoles by heatshock given 3 to 4 h prior to amputation (Figure S1C and Table S1).…”

Identity of the avian wing digits: Problems resolved and unsolved

“…In the anuran forelimb, despite anatomical descriptions of the digits referring to them as I, II, III, and IV (Romer and Parsons, 1970), the position of the primary axis in the forelimb (Oster et al, 1988) combined with expression of Hoxd11 in the anteriormost digit (in Xenopus; Satoh et al, 2006) indicates the presence of II, III, IV, and V digit identities. Another case of digit identity conflict, remarkably similar to that in birds, occurs in Chalcides chalcides, the Italian three-toed skink.…”