Differential expression of transforming growth factor-alpha during prenatal development of the mouse.

Transforming growth factors (TGFs) are differentially expressed in the mouse during neonatal development. Highest levels are seen early at Day 7, and lower levels, at Day 13. Both small- and large-molecular-weight forms of TGF are found; they share many biochemical properties with rat TGF-alpha, including a similar high-pressure liquid chromatography elution profile. Although the embryo-derived activities compete with epidermal growth factor for binding to epidermal growth factor membrane receptors, they are immunologically distinct from epidermal growth factor. These embryonic polypeptides, however, do cross-react in a competitive radioimmunoassay developed using a synthetic peptide corresponding to the carboxy-17 amino acids of rat TGF-alpha as the immunogen. The highly conserved TGF-alpha family of peptides produced by some tumor cells may therefore represent derepressed forms of these embryonic growth factors. A functional role in neonatal development is proposed.