A Xenopus type I activin receptor mediates mesodermal but not neural specification during embryogenesis.
Activins and other ligands in the TGFbeta superfamily signal through a heteromeric complex of receptors. Disruption of signaling by a truncated type II activin receptor, XActRIIB (previously called XAR1), blocks mesoderm induction and promotes neuralization in Xenopus embryos. We report the cloning and characterization of a type I activin receptor, XALK4. Like truncated XActRIIB, a truncated mutant (tXALK4) blocks mesoderm formation both in vitro and in vivo; moreover, an active form of the receptor induces mesoderm in a ligand-independent manner. Unlike truncated XActRIIB, however, tXALK4 does not induce neural tissue. This difference is explained by the finding that tXALK4 does not block BMP4-mediated epidermal specification, while truncated XActRIIB inhibits all BMP4 responses in embryonic explants. Thus, the type I and type II activin receptors are involved in overlapping but distinct sets of embryonic signaling events.
Chang
C
C
Department of Molecular Embryology, The Rockefeller University, New York, NY 10021-6399, USA.
Wilson
P A
PA
Mathews
L S
LS
Hemmati-Brivanlou
A
A
D029404:Activin Receptors; D030201:Activin Receptors, Type I; D028341:Activins; D000595:Amino Acid Sequence; D000818:Animals; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D002454:Cell Differentiation; D003001:Cloning, Molecular; D004475:Ectoderm / Q000166:cytology; D004627:Embryonic Induction; D000078404:Epidermal Cells; D004817:Epidermis / Q000196:embryology; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D017403:In Situ Hybridization; D007265:Inhibins / Q000494:pharmacology*; D008648:Mesoderm / Q000166:cytology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D017978:Receptors, Growth Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction; D014981:Xenopus / Q000196:embryology; D029867:Xenopus Proteins
D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D017978:Receptors, Growth Factor; D029867:Xenopus Proteins; C525812:bmp4 protein, Xenopus; D028341:Activins; D007265:Inhibins; D029404:Activin Receptors; D030201:Activin Receptors, Type I