Identification of TGF-β-related genes in the early chick embryo.
Transforming growth factor-β (TGF-β)-related genes have been postulated as possible mesoderm inducers in lower vertebrates. Activin, a member of the TGF-β family has been recently suggested to be directly involved in the induction of axial mesoderm in frogs and birds. Nodal, a novel TGF-β-like gene, seems to be essential for mesoderm formation in mice. In this work we have tried to characterize which growth factors of the TGF-β family are involved in the initial stages of differentiation of the chick embryo. Using degenerate primers to specific regions of the TGF-β super family in polymerase chain reactions (PCR), we have identified both TGF-β2 and TGF-β3 transcripts in early stages of chick development. In addition, we have identified a new gene which is transcribed during early chick development. We have called this gene Vgc1 since it is probably the chick homologue of the mouse Vg-related gene Vgrl. RNA coding for the Vgcl gene was detected by RNAse protection in early stage X blastoderms, gastrula and 3-day-old embryos. In situ hybridization experiments further indicate that Vgcl RNA is distributed uniformly throughout the various regions of the chick gastrula. The role of Vgcl in early chick development remains to be established.