EMBRYONIC EXPRESSION OF EPH SIGNALING FACTORS IN XENOPUS

Cellular communication in the developing embryo is mediated by recepto r-ligand interactions at the cell surface. Receptor protein tyrosine k inases (RTKs) have been shown to play a critical role in the developme nt of the vertebrate embryo. The eph receptors are a large subclass of RTKs for which a corresponding ligand family has only recently been d escribed. The restricted expression patterns of several eph receptors imply roles for these molecules in early vertebrate development. We ha ve isolated both a ligand of the eph ligand family (ELF), that we have named XELF-a, and an eph-related receptor, XE10, the likely homolog o f the murine eck/Sek-2 receptor. At least two forms of the XELF-a tran script are present in the developing embryo. A truncated form of the X ELF-a ligand, XELF-a', is the first ELF ligand isolated that lacks bot h the membrane-spanning and membrane-anchoring motifs conserved among this family, suggesting that ELF ligands can function as fully soluble molecules in vivo. XELF-a and XE10 are expressed maternally and throu ghout early embryogenesis, while XELF-a' is only expressed zygotically . The dynamic expression patterns of these signalling molecules, in bo th mesoderm and neurectoderm, suggest that they may play a role in the patterning of the early vertebrate embryo.