Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Activin Receptors
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Activin Receptors, Type I
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Activins
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Amino Acid Sequence
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Animals
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Bone Morphogenetic Protein 4
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Bone Morphogenetic Proteins / pharmacology
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Cell Differentiation
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Cloning, Molecular
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Ectoderm / cytology
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Embryonic Induction*
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Epidermal Cells
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Epidermis / embryology
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Gene Expression Regulation, Developmental / genetics
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In Situ Hybridization
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Inhibins / pharmacology*
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Mesoderm / cytology*
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Molecular Sequence Data
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Mutagenesis, Site-Directed / genetics
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Receptors, Growth Factor / chemistry
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Receptors, Growth Factor / genetics
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Receptors, Growth Factor / metabolism*
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Sequence Alignment
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Signal Transduction
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Xenopus / embryology
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Xenopus Proteins
Substances
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Bone Morphogenetic Protein 4
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Bone Morphogenetic Proteins
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Receptors, Growth Factor
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Xenopus Proteins
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bmp4 protein, Xenopus
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Activins
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Inhibins
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Activin Receptors
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Activin Receptors, Type I