Synthesis of Serum Albumin, Prealbumin, α-Foetoprotein, α₁-Antitrypsin and Transferrin by the Human Yolk Sac

Abstract

BOTH in the chick embryo and in the rat foetus, the yolk sac is an important, biologically active membrane throughout almost all of antenatal development. In the chick, the yolk sac envelops the great mass of yolk present in the egg and absorbs yolk material for embryo nutrition. The yolk sac in the rat forms one of the foetal membranes that encompass and protect the foetus, and during the last quarter of gestation it lies in direct apposition to the maternal endometriurn. In both these species, the yolk sac synthesizes serum proteins^1,2: in both, a serum iron-binding globulin and a serum α-globulin specific for the embryo or foetus are produced. The yolk sac of the chick also synthesizes serum albumin², a feat apparently not matched by the rat yolk sac¹. The yolk sac of the human embryo, on the other hand, is a relatively small vesicle at the height of its development, and, it soon degenerates to become atretic by the end of the first trimester of gestation³. The observation that the chick and rat yolk sacs can synthesize serum proteins prompted the present investigation into the possibility that the human yolk sac, too, might do so during its relatively brief existence as a well developed structure.