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An antiserum was prepared in rabbit against rat visceral yolk sac endoderm. The initial injection was of a ConA-Sepharose purified fraction of endoderm, and subsequent injections were of whole endoderm. The antiserum was found to be a potent rat teratogen in vivo, the most common defects observed being anophthalmia and hydrocephaly.Using rat whole embryo culture, the antiserum was demonstrated to induce dysmorphogenesis and growth retardation in a concentration dependent manner. The most frequent abnormalities were of the optic primordia, suggesting a similar embryonic response in vitro to that observed in vivo.In further culture experiments, the antiserum was shown to inhibit macromolecule (I-labelled PVP) uptake by the visceral yolk sac, an essential process in embryonic nutrition. This effect of impaired yolk sac-mediated nutrition confirms previous observations using anti-whole yolk sac antiserum (Freeman et al. 1982), and it is proposed as the primary cause of teratogenesis.In order to identify the yolk sac antigen(s) involved in the teratogenic response, yolk sac endoderm peptides were separated by PAGE and electrophoretically transferred to nitrocellulose for analysis. With an enzyme linked immunoassay, the antiserum was observed to cross-react with a single 30 kd peptide, demonstrated by a ConA-binding technique to be a glycopeptide. Control serum showed no evidence of cross-reaction with yolk sac peptides.

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