Mesenchyme with fgf-10 Expression Is Responsible for Regenerative Capacity in Xenopus Limb Buds

Abstract

A young tadpole of an anuran amphibian can completely regenerate an amputated limb, and it exhibits an ontogenetic decline in the ability to regenerate its limbs. However, whether mesenchymal or epidermal tissue is responsible for this decrease of the capacity remains unclear. Moreover, little is known about the molecular interactions between these two tissues during regeneration. The results of this study showed that fgf-10 expression in the limb mesenchymal cells clearly corresponds to the regenerative capacity and that fgf-10 and fgf-8 are synergistically reexpressed in regenerating blastemas. However, neither fgf-10 nor fgf-8 is reexpressed after amputation of a nonregenerative limb. Nevertheless, nonregenerative epidermal tissue can reexpress fgf-8 under the influence of regenerative mesenchyme, as was demonstrated by experiments using a recombinant limb composed of regenerative limb mesenchyme and nonregenerative limb epidermis. Taken together, our data demonstrate that the regenerative capacity depends on mesenchymal tissue and suggest that fgf-10 is likely to be involved in this capacity.

Beyond early development: Xenopus as an emerging model for the study of regenerative mechanisms

“…The importance for Fgf signalling has also been functionally demonstrated for limb regeneration. A correlation between Fgf-10 expression in the limb bud mesenchyme and the ability to regenerate has been observed (Yokoyama et al, 2000) and a gain-offunction approach showed that Fgf-10 is indeed responsible for the regenera-tive capacity . Beads soaked in recombinant Fgf-10 protein and then placed in the stump of a nonregenerative limb (st. 56) were able to restore some regenerative capacity to the limb ).…”

“…To determine whether the mesenchyme or the epidermis was responsible for the decline in regeneration success, Yokoyama et al created recombinant limbs, combining mesenchyme and epidermis from regeneration competent (st. 52) and incompetent (st. 56) limbs (Yokoyama et al, 2000). The regenerative mesenchyme was able to induce fgf-8 expression in the regenerative incompetent epidermis and as a consequence, regeneration could proceed.…”

“…There is a clear difference in the initial mechanism of dorsal-ventral patterning although later restricted expression of lmx1 in the dorsal mesoderm appears to be the same across tetrapod species (Christen and Slack, 1998;Matsuda et al, 2001). Genes involved in defining the proximal-distal (P-D) axis such as fgf-10 (Yokoyama et al, 2000) and fgf-8 are expressed in the distal mesenchyme and in the apical region of the limb bud, respectively (Christen and Slack, 1997). However the distal mesenchymal expression of the Bmp inhibitor Gremlin in mouse limbs, which regulates the growth of the limb by means of inhibitory effects on the AER specific Fgf-8 (Verheyden and Sun, 2008), is not seen in Xenopus (Pearl et al, 2008).…”

Mechanisms of urodele limb regeneration

“…Yokoyama et al. (2000) demonstrated that mesenchymal Fgf10 maintains Fgf8 expression by the AEC in regenerating Xenopus limb buds, and vice versa. Xenopus limbs lose the power of regeneration as they differentiate and form a blastema of fibroblast‐like cells (Dent, 1962; Van Stone, 1964).…”

“…Xenopus limbs lose the power of regeneration as they differentiate and form a blastema of fibroblast‐like cells (Dent, 1962; Van Stone, 1964). This loss is accompanied by a loss of Fgf10 expression by the fibroblastema and loss of Fgf8 expression by the AEC (Yokoyama et al., 2000) due to changes in the limb bud cells related to their differentiation (Filoni, Bernardini, & Cannata, 1991; Sessions & Bryant, 1988). Fgf10‐soaked beads placed on the amputation surface of regeneration‐deficient limbs of Xenopus late tadpoles restore Fgf8 expression in the AEC and digit regeneration, although not more proximal structures (Yokoyama, Ide, & Tamura, 2001).…”