A Ligand for ALK7

Reissmann et al. examined the roles of the transforming growth factor-β (TGF-β) receptor superfamily proteins ALK7, ALK4, and ActRIIB in Xenopus development. Their results indicated that the ALK7 receptor bound Nodal and Xenopus Nodal-related 1 (Xnr1), and that Nodal-dependent signaling through ALK7 required ActRIIB for transducing signals. The presence of Cripto, an extracellular protein, increased Nodal-dependent signaling through ALK7 and ActRIIB. Additionally, Cripto was essential for Nodal-dependent activation of the Activin receptor ALK4. Thus, it appears that ALK4 can mediate vertebrate development through the selective use of at least two different ligands. Also, a Nodal and Xnr1 might act as physiologically relevant ligands for the previously described orphan receptor ALK7. E. Reissmann, H. Jörnvall, A. Blokzijl, O. Andersson, C. Chang, G. Minchiotti, M. Graziella Persico, C. F. Ibáñez, A. H. Brivanlou, The orphan receptor ALK7 and the Activin receptor ALK4 mediate signaling by Nodal proteins during vertebrate development. Genes Dev . 15 , 2010-2022 (2001). [Abstract] [Full Text]