9507049 Servetnick Mesoderm induction in Xenopus laevis embryos is mediated by a number of diffusible signals, including members of the fibroblast growth factor (FGF) family of signalling molecules. Members of the FGF family show mesoderm inducing activity in vitro, FGF's are expressed at the appropriate time and place in embryonic development, and inactivation of FGF receptors leads to defects in mesoderm formation in vivo. The FGF signalling pathway interacts with other signalling pathways that are thought to operate in mesoderm induction (including members of the TGF-beta superfamily), though the nature of these interactions is poorly understood. The proposed project focuses on a cDNA clone encoding a novel FGF receptor, termed F37, from early Xenopus embryos. Preliminary data show that F37 mRNA is present in the unfertilized egg, and remains present through early development, consistent with a role for its cognate FGF receptor in mesoderm induction. Because experiments to date have characterized only a single FGF receptor present in the Xenopus embryo during the period of mesoderm induction, the presence of this second FGF receptor mRNA suggests that binding of FGF's to different FGF receptors, or the interactions between different FGF receptors, may play a role in the induction or patterning of mesoderm. A full length F37 clone will be isolated, sequenced, and its embryonic expression pattern will be characterized both temporally and spatially, using RNA blots and whole mount is situ hybridization. To determine whether the regulation of F37 expression is similar to, or different from, previously characterized Xenopus FGF receptors, the expression of all the Xenopus FGF receptor mRNAs will be analyzed in several ways. Using RNA blots, 1) the expression pattern of the FGF receptor mRNAs in isolated animal caps will be determined; and 2) the timing of polyadenylation (and presumably translation) of the various FGF receptor mRNAs during development will be determined. Finally, experiments will be performed to test the hypothesis that over expression of FGF receptors can extend the period of competence to respond to mesoderm induction. ***
