Cloning and developmental expression of the chick type II and type III TGF beta receptors

To address the role of peptide growth factors in chick organogenesis, we have focused on TGF beta 2 and have cloned the chick Type II and Type III TGF beta receptors. The chick Type II receptor is a serine/threonine kinase with a ligand binding profile identical to the human receptor and a divergent N-terminus when compared to the mammalian receptors. The chick Type III receptor is a beta-glycan that demonstrates a binding profile identical to the rat receptor and contains a single transmembrane spanning domain and short cytoplasmic tail that are highly conserved when compared to the mammalian receptors. Both the Type II and Type III TGF beta receptors are coexpressed during chick embryogenesis in the developing heart, lung, and eye, and are developmentally upregulated in parallel in the heart and lung. Levels of both receptor proteins and mRNAs also increase in cardiocytes cultured from different developmental stages, in agreement with the increase in Type II and Type III receptor mRNA levels observed in the developing heart. Although exhibiting different temporal or spatial profiles from the receptors, TGF beta 2 is also expressed in the developing heart, lung, and eye. These findings are consistent with recent data indicating that co-expression of both the Type II and Type III TGF beta receptors is required for high affinity binding of TGF beta 2 by the Type II receptor and suggest that TGF beta 2 and the Type II and Type III TGF beta receptors participate in heart, lung, and eye development.