THE XENOPUS PLATELET-DERIVED GROWTH-FACTOR ALPHA-RECEPTOR - CDNA CLONING AND DEMONSTRATION THAT MESODERM INDUCTION ESTABLISHES THE LINEAGE-SPECIFIC PATTERN OF LIGAND AND RECEPTOR GENE-EXPRESSION

We have cloned the Xenopus PDGF alpha receptor cDNA and have used this clone, along with cDNA encoding PDGF A, to examine their expression p attern in Xenopus embryos and to determine the factors responsible for lineage specificity. Recombinant Xenopus alpha receptor expressed in COS cells exhibits PDGF-A-dependent tyrosine kinase activity. We find that receptor mRNA is present in cultured marginal zone tissue explant s and in animal cap tissue induced to form mesoderm either by grafting to vegetal tissue or by treatment with recombinant activin A. In cont rast, PDGF A mRNA is expressed in cultured, untreated animal cap tissu e and is suppressed by mesoderm induction. These results suggest that ectodermally produced PDGF A may act on the mesoderm during gastrulati on and that mesoderm induction establishes the tissue pattern of ligan d and receptor expression.