Abstract

PIP: New information on alpha fetoprotein (AFP) sites of synthesis are presented in this letter to the editor. Traces of AFP were synthesized by not only the human yolk sac and liver but also, in 6/9 human embryos and fetuses studied, by the gastrointestinal tract. Also, sharks synthesize an AFP similar to that of the human in molecular size and electrophoretic mobility. Although small amounts of AFP are synthesized by sharks in the liver, the greatest site of synthesis is actually the stomach, with smaller amounts synthesized in the intestinal mucosa; no synthesis was observed in the shark yolk sac. Thus it appears that early in evolution the site of synthesis of AFP was mainly in the gastrointestinal tract and that during evolution 2 outgrowths of the entoderm (the liver and yolk sac) became the major sites of AFP synthesis; in birds the synthesis seems to be restricted to the yolk sac, with only traces found in the gastrointestinal tract.