Tissue-specific expression of onco-fetal antigens during embryogenesis.

It has become evident from recent literature that especially in tumor virus systems, cell transformation leads to an arrest of differentiation or to a retrodifferentiation. This may be reflected by the expression of embryonic antigens and it is therefore particularly important to characterize such antigens according to their specificity as well as to their specificity during embryogenesis. We have demonstrated the expression of embryonic antigens which are cross-reactive in avian fibroblasts transformed either by Rous sarcoma virus or by methylcholanthrene. This paper is intended to demonstrate that these embryonic antigens are detected only at a certain period of embryogenesis and particularly in muscle cells. They are detected only occasionally or not at all in cells of other tissues such as brain, liver, lung, and the digestive organs. These antigens are absent from the target cells before transformation and are consequently induced by the transforming agent, either viral or chemical. Therefore, these results suggest that by transformation mechanism, cells become specifically reverted to an earlier stage of differentiation (retrodifferentiation).