Isolation and characterization of a transforming growth factor-beta Type II receptor cDNA from Xenopus laevis.

Transforming Growth Factor-beta (TGF-beta) and their receptors have been characterized from many organisms. Two TGF-beta signaling receptors called Type I and II have been described for various ligands of the superfamily from organisms ranging from Drosophila to humans. In Xenopus laevis, TGF-beta2 and 5 have been reported and presumably, play important roles during early development. Several Type I and type II receptors for many ligands of the TGF-beta superfamily except TGF-beta type II receptor (TbetaIIR), have been characterized in Xenopus laevis. A chemical cross linking experiment using iodinated TGF-beta1 and -beta5, revealed four specific binding proteins on XTC cells. In order to understand the TGF-beta involvement during Xenopus development, a TGF-beta type II receptor (XTbetaIIR) has been isolated from a XTC cDNA library. XTbetaIIR was a partial cDNA lacking a portion of the signal peptide. The sequence analysis and homology comparison with the human TbetaIIR revealed 67% amino acid similarity in the extra cellular domain, 60% similarity in the transmembrane domain and 87% similarity in the cytoplasmic kinase domain, suggesting that XTbetaIIR is a putative TGF-beta type II receptor. In addition, the consensus amino acid motif for serine threonine receptor kinases was also present. Further, a dominant negative expression construct lacking the cytoplasmic kinase domain (engineered with the signal peptide from human TGF-beta type II receptor), was able to abolish TGF-beta mediated induction of a luciferase reporter plasmid, in a transient cell transfection assay. This substantiates the notion that XTbetaIIR cDNA can act as a receptor for TGF-beta. RT-PCR analysis using RNA isolated from various developmental stages of Xenopus laevis revealed expression of this gene in all the early stages of development and in the adult organs, except in stages 46/48.