A Xenopus type I activin receptor mediates mesodermal but not neural specification during embryogenesis

Development. 1997 Feb;124(4):827-37. doi: 10.1242/dev.124.4.827.


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

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Activin Receptors
  • Activin Receptors, Type I
  • Activins
  • Amino Acid Sequence
  • Animals
  • Bone Morphogenetic Protein 4
  • Bone Morphogenetic Proteins / pharmacology
  • Cell Differentiation
  • Cloning, Molecular
  • Ectoderm / cytology
  • Embryonic Induction*
  • Epidermal Cells
  • Epidermis / embryology
  • Gene Expression Regulation, Developmental / genetics
  • In Situ Hybridization
  • Inhibins / pharmacology*
  • Mesoderm / cytology*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed / genetics
  • Receptors, Growth Factor / chemistry
  • Receptors, Growth Factor / genetics
  • Receptors, Growth Factor / metabolism*
  • Sequence Alignment
  • Signal Transduction
  • Xenopus / embryology
  • Xenopus Proteins


  • Bone Morphogenetic Protein 4
  • Bone Morphogenetic Proteins
  • Receptors, Growth Factor
  • Xenopus Proteins
  • bmp4 protein, Xenopus
  • Activins
  • Inhibins
  • Activin Receptors
  • Activin Receptors, Type I