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Abstract
SUMMARY Mevalonic acid-2-C 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.
Highlights
The nonsaponifiable fraction (NSF) obtained from pooled embryos and from pooled yolk sacmembrane fractions isolatedon the tenth dayof incubation was fractionated in each instance by alumina columnchromatography using l50 galumina,activity
Another phase of sterol syntheses may occur in the yolk sac beginning on the 12th day of incubation since arapidincreasein thetotalactivity was observed in theNSF of this component.This is further supported by the observation that the total activityin the embryo rapidly increased shortly after theincrease was observed in the yolk sac.This latter synthesis of a NSF may be coupled with an increased transfer of unlabeled sterol from the yolk since the specific activity of both the yolk sac and embryo decreased during this period
There hasbeen uncertainty asto whether or not cholesterol biosynthesis occurs during the development of the chick embryo [1,2,4], theincorporation of acetatc-Cl4 into cholesterol and desmosterol has been demonstrated during the latter half of the incubation [9]
Summary
A nonsaponifiable fraction(NSFc)ontaining labeled components was isolated from the yolk sac and from the embryo throughout the remainder of the incubation.Thespecific activity of both the yolksac and embryonicNSFincreased during the first 3 days following injection of the labeled precursor and decreased from the remainder of the incubation. (4)after studying the levels of free and esterified cholesterol in incubating eggs, concluded that there isno net cholesterol synthesis but that yolk cholesterol is esterified andtransferredtotheembryo.Thistransferis first observed about the tenth dayof incubation and is especially active 2 days prior to hatching. The present work was undertaken to determine whether or not mevalonic a ~ i d - 2 - C ' ~(MVA-2-CI4), a precursor of sterols ( 5 ) ,furnishes labeled components of the nonsaponifiable fraction (NSF) in the developing chick embryo.Concurrently,astudy of the levels of.
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