Identification and Characterization of a Transient Embryonic Antigen in the Chick

Abstract

<p>Transient embryonic antigens have been described in many systems in development. Although their function has not yet been elucidated their detection in the embryo but not in the adult state suggests a direct relationship with embryogenesis. The present investigation was undertaken in order to characterize and study a transient antigen (TEA) in chick embryo brain extracts.</p> <p>TEA was identified by using specific antiserum prepared against 9 day embryonic chick brain extract. The antiserum was first absorbed with adult serum, liver and kidney extracts to remove non-neural antibodies. Then adult brain extract was added to remove antibodies directed against adult neural antigens. This antiserum (TAS) was then considered to be both embryo and neural specific. However, subsequent studies demonstrated TEA in extracts of 9 day embryonic liver, kidney and serum in concentrations similar to that found in 9 day brain extracts. TEA was therefore not specific to neural tissue as initially considered.</p> <p>TEA demonstrated anodal migration in an electric field, similar to an alpha-globulin at pH 8.6. Ontogenic studies using immunoelectrophoresis and the quantitative technique of rocket immunoelectrophoresis were performed. TEA was present by 2 days incubation, and an initial peak at 4 days was noted. From day 6 on, TEA accumulated until a maximum concentration was reached at 12 days incubation. TEA levels then decreased until it could no longer be detected in 20 day embryo or adult brain extracts.</p> <p>Molecular exclusion chromatography revealed the molecular weight of TEA to be 73,000 daltons. Isoelectric focusing demonstrated the isoelectric point at pH 4.8. The antigenic site of the TEA molecule was considered to be proteinaceous on the basis of its sensitivity to pronase; however it was not hydrolysed by either trypsin of chymotrypsin.</p> <p>Based on the ontogenic pattern and the physical and chemical characteristics it was concluded that TEA was a chick alpha-fetoprotein. The possible role of TEA in embryonic development and the mechanisms of its regulation were also discussed.</p>