Free amino acids in the early cleavage stages of the rabbit egg

In the first half of gestation, mouse yolk sac contains levels of N-acetyl-β-hexosaminidase activity and a ratio of N-acetyl-β-hexosaminidase: β-glucuronidase much higher than those of other embryonic tissues or the decidua. The properties of the yolk sac enzyme are very similar to those in the other tissues, suggesting that the observed difference in activity is quantitative rather than qualitative. In blastocyst cultures, the vesicular growths derived from the inner cell mass possess patterns of N-acetyl-β-hexosaminidase activity similar to yolk sac in vivo, but different from trophoblast cells developing in the same cultures. It is therefore proposed that the vesicular growths contain at least some differentiated yolk sac cells.