The biosynthesis of cholesterol in the developing chick embryo*

Abstract

Mevalonic acid-2-C14 was injected into the yolk of incubating fertile hens' eggs on the sixth day of incubation. A nonsaponifiable fraction (NSF) containing labeled components was isolated from the yolk sac and from the embryo throughout the remainder of the incubation. The specific activity of both the yolk sac and embryonic NSF increased during the first 3 days following injection of the labeled precursor and then decreased from the remainder of the incubation. The total activity of the yolk sac and embryonic NSF increased during the incubation. The largest increment in total radioactivity of the yolk sac NSF occurred after the 12th day of incubation and that of the embryonic NSF after the 15th day. A high level of labeled squalene was found in the yolk sac NSF. Labeled cholesterol was found in both the yolk sac and embryo. About 3% of the recovered activity of the NSF was found in the brain tissue of chicks hatched from injected eggs.