INVESTIGATIONS INTO MECHANISMS OF AMINO-ACID SUPPLY TO THE RAT EMBRYOUSING WHOLE-EMBRYO CULTURE

The technique pioneered by D.A.T. New for the in vitro culture of earl y post-implantation rat embryos has been used to study nutritional mec hanisms during early organogenesis. The results indicate that the prin cipal route for amino acid supply to the 8.5- to 11.5-day embryo invol ves the endocytosis of proteins into cells of the visceral yolk sac en doderm, their digestion in lysosomes, and transmission of the amino ac ids to the growing embryo. Free amino acids constitute a comparatively unimportant source. Inhibition of either endocytosis or intralysosoma l proteolysis diminishes amino acid supply to the embryo, and this can result in embryonic death or maldevelopment during organogenesis.