title: Ectopic EphA4 receptor induces posterior protrusions via FGF signaling in Xenopus embryos.
abstract: The Eph family of receptor tyrosine kinases regulates numerous biological processes. To examine the biochemical and developmental contributions of specific structural motifs within Eph receptors, wild-type or mutant forms of the EphA4 receptor were ectopically expressed in developing Xenopus embryos. Wild-type EphA4 and a mutant lacking both the SAM domain and PDZ binding motif were constitutively tyrosine phosphorylated in vivo and catalytically active in vitro. EphA4 induced loss of cell adhesion, ventro-lateral protrusions, and severely expanded posterior structures in Xenopus embryos. Moreover, mutation of a conserved SAM domain tyrosine to phenylalanine (Y928F) enhanced the ability of EphA4 to induce these phenotypes, suggesting that the SAM domain may negatively regulate some aspects of EphA4 activity in Xenopus. Analysis of double mutants revealed that the Y928F EphA4 phenotypes were dependent on kinase activity; juxtamembrane sites of tyrosine phosphorylation and SH2 domain-binding were required for cell dissociation, but not for posterior protrusions. The induction of protrusions and expansion of posterior structures is similar to phenotypic effects observed in Xenopus embryos expressing activated FGFR1. Furthermore, the budding ectopic protrusions induced by EphA4 express FGF-8, FGFR1, and FGFR4a. In addition, antisense morpholino oligonucleotide-mediated loss of FGF-8 expression in vivo substantially reduced the phenotypic effects in EphA4Y928F expressing embryos, suggesting a connection between Eph and FGF signaling.
authors.affiliation: Regulation of Cell Growth Laboratory, National Cancer Institute-Frederick, Frederick, Maryland 21702, USA.
authors.forename: Eui Kyun
authors.initials: EK
authors.lastname: Park
authors.forename: Neil
authors.initials: N
authors.lastname: Warner
authors.forename: Yong-Sik
authors.initials: YS
authors.lastname: Bong
authors.forename: David
authors.initials: D
authors.lastname: Stapleton
authors.forename: Ryu
authors.initials: R
authors.lastname: Maeda
authors.forename: Tony
authors.initials: T
authors.lastname: Pawson
authors.forename: Ira O
authors.initials: IO
authors.lastname: Daar
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D051379:Mice; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D036122:Receptor, EphA4 / Q000096:biosynthesis / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry; D014981:Xenopus; D018909:src Homology Domains
chemical_list: D012333:RNA, Messenger; D051524:Fibroblast Growth Factor 8; D014443:Tyrosine; D005346:Fibroblast Growth Factors; D012313:RNA; D036122:Receptor, EphA4