Placental polyploidization: a comparative study in the mouse and the guinea pig.

The trophoblastic and endodermal tissues of the guinea pig were cytophotometrically examined at two stages of development, either shortly after the primary trophoblastic giant cell layer had degenerated (Sansom and Hill, 1931) and the visceral yolk sac was starting to form (Kaufman and Davidoff, 1977) (c. 10.5 days p.c. at the egg cylinder stage) or later in gestation, when the yolk sac was well developed (c. 17.5 days p.c. at the neural tub closure stage). Subsequently, the trophoblastic and endodermal tissues of the mouse were analysed in a manner identical to those of the guinea pig. Finally, the nuclear DNA content values from the analysis of the tissues of each species were compared. The results thus obtained indicate firstly that, in the guinea pig, polyploid nuclei also appear within visceral endoderm after the primary trophoblastic giant cells degenerate and, secondly, that placental specialization in the rodents, as originally defined by Mossman (1937), apparently tends towards lower levels of polyploidy within trophoblast and higher levels within the derivatives of visceral endoderm.