FGF-8 IS ASSOCIATED WITH ANTEROPOSTERIOR PATTERNING AND LIMB REGENERATION IN XENOPUS

FGF-8 has attracted attention particularly because of its importance f or limb development in the chick and mouse, although it also has a num ber of earlier expression domains in these species. We have now cloned an FGF-8 homologue from Xenopus in which it is easier to do functiona l studies on early development. There is no maternal expression, while zygotic expression is highest in the gastrula and neurula stages. XFG F-8 is expressed as a ring around the blastopore and subsequently in t he tail bud. There are several domains in the head including the hatch ing 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 re gion with a similar ability to stimulate mesenchymal outgrowth. The me soderm-inducing activity of XFGF-8 is somewhat lower than that of othe r FGFs, while the posteriorizing activity is similar. These difference s are probably due to the different receptor specificity. The posterio r expression and high posteriorizing activity suggest that XFGF-8 cont ributes to the patterning of the anterior-posterior axis by FGF family members during gastrulation. In contrast to the amniotes, Xenopus lim b buds can regenerate following damage. We show that regeneration is c orrelated with the reexpression of XFGF-8 in the distal epidermis, sug gesting that this ability is critical for successful limb regeneration . (C) 1997 Academic Press.