EXPRESSION AND FUNCTIONS OF FGF-3 IN XENOPUS DEVELOPMENT

We have analyzed the expression pattern of the Xenopus FGF-3 gene duri ng early development and examined its biological activity in three dif ferent bioassays using Xenopus embryos. We show that from the early ga strula stage there is a domain of expression around the blastopore whi ch becomes a posterior domain as the blastopore closes. An anterior ec todermal domain becomes detectable from mid-gastrula stages in the pro spective hind-brain, and there are several later domains of expression : the midbrain-hindbrain junction, the otocyst, the pharyngeal pouches and the tailbud region. By using double whole-mount in situ hybridiza tions we show that the XFGF-3 expression in the brain is dynamically r egulated both in time and space during development. The anterior domai n of early neurula stage embryos corresponds to the prospective rhombo meres 3-5. By the time the neural tube is closed, XFGF-3 expression is restricted to r4 and later a new domain of expression is established at the midbrain/hindbrain junction. In addition, we show that, despite its difference in receptor specificity, XFGF-3 can induce the formati on of mesoderm from animal caps similarly to other FGFs. It also displ ays a posteriorizing activity on whole embryos similar to other FGFs. Although the absence of maternal expression makes it unlikely that XFG F-3 is involved in mesoderm induction in vivo, its posterior domain of expression during gastrulation and its posteriorizing activity sugges ts that it participates in the maintenance of mesodermal gene expressi on and in the FGF mediated patterning of the anteroposterior axis duri ng gastrulation.