Serum Protein Synthesis by Embryonic and Neonatal Chicks

Abstract

The chick embryo is an ideal organism for the study of serum protein synthesis since it is separated from the maternal circulation during its development. Heim and Schechtman(1) and others(2,3) have indicated that both qualitative and quantitative changes occur in the sera of developing embryos and neonatal chicks. It has not been determined what part, if any, of these changes is the result of protein synthesis by the animal, and what part is the result of absorption of proteins from the yolk(4). This problem has been investigated in our laboratory, using incorporation of radioactively labeled amino acid as a criterion for protein production, and autoradiography of immunoelectrophoretic patterns(5) to identify the labeled proteins.

Materials and methods. Animals. Seventeen- to nineteen-day-old chick embryos were given 100 μc (∼50 μg) S-35 methionine intravenously; 3-day-old and 12-day-old chicks received 200 μc intraperitoneally. All animals were bled one day following injection.

Immunoelectrophoresis and autoradiography. Microimmunoelectrophoretic patterns(6) of experimental sera alone and mixed with chicken globulin (obtained by salt fractionation) or with adult chicken serum were prepared. Rabbit antisera against chicken globulin or against whole chicken serum were employed to develop the precipitation lines. The mixtures of experimental sera with “carrier”protein solutions were used in order to obtain reproducible immunoelectrophoretic patterns. It will be seen that the patterns obtained with experimental sera varied with the age of the animals. Autoradiographs were made as previously described(5).

Results. The antisera employed demonstrated 5 proteins of gamma mobility (Fig. 1), in addition to a prealbumin, albumin, and several proteins in the α and β regions. One of these was the major γ-globulin, which has been shown to contain antibody activity(7). A second was the β ₂-macroglobulin, verified by ultracentrifugation(8). The properties and function of the remaining 3 proteins are not known.