EXPRESSION OF A NOVEL FGF IN THE XENOPUS EMBRYO - A NEW CANDIDATE INDUCING FACTOR FOR MESODERM FORMATION AND ANTEROPOSTERIOR SPECIFICATION

We have cloned and sequenced a new member of the fibroblast growth fac tor family from Xenopus laevis embryo cDNA. It is most closely related to both mammalian kFGF (FGF-4) and FGF-6 but as it is not clear wheth er it is a true homologue of either of these genes we provisionally re fer to it as XeFGF (Xenopus embryonic FGF). Two sequences were obtaine d, differing by 11% in derived amino acid sequence, which probably rep resent pseudotetraploid variants. Both the sequence and the behaviour of in vitro translated protein indicates that, unlike bFGF (FGF-2), Xe FGF is a secreted molecule. Recombinant XeFGF protein has mesoderm-ind ucing activity with a specific activity similar to bFGF. XeFGF mRNA is expressed maternally and zygotically with a peak during the gastrula stage. Both probe protection and in situ hybridization showed that the zygotic expression is concentrated in the posterior of the body axis and later in the tailbud. Later domains of expression were found near the midbrain/hindbrain boundary and at low levels in the myotomes. Bec ause of its biological properties and expression pattern, XeFGF is a g ood candidate for an inducing factor with possible roles both in mesod erm induction at the blastula stage and in the formation of the antero posterior axis at the gastrula stage.