FGF-8 is associated with anteroposterior patterning and limb regeneration in Xenopus

FGF-8 has attracted attention particularly because of its importance for limb development in the chick and mouse, although it also has a number of earlier expression domains in these species. We have now cloned an FGF-8 homologue from Xenopus in which it is easier to do functional studies on early development. There is no maternal expression, while zygotic expression is highest in the gastrula and neurula stages. XFGF-8 is expressed as a ring around the blastopore and subsequently in the tail bud. There are several domains in the head including the hatching gland, the branchial clefts, and the midbrain-hindbrain border. At later stages there is a prominent band of expression in the limb bud epidermis. Although there is no morphological apical ridge, this band of expression suggests that the Xenopus limb bud contains a cryptic region with a similar ability to stimulate mesenchymal outgrowth. The mesoderm-inducing activity of XFGF-8 is somewhat lower than that of other FGFs, while the posteriorizing activity is similar. These differences are probably due to the different receptor specificity. The posterior expression and high posteriorizing activity suggest that XFGF-8 contributes to the patterning of the anterior-posterior axis by FGF family members during gastrulation. In contrast to the amniotes, Xenopus limb buds can regenerate following damage. We show that regeneration is correlated with the reexpression of XFGF-8 in the distal epidermis, suggesting that this ability is critical for successful limb regeneration.