A light and electron microscopy study of the yak placentome.

In order to clarify and reveal the morphological characteristics of yak placentomes, placentomes obtained from 151 to 180 days of pregnant yaks were observed using light microscopy and scanning and transmission electron microscopy. The results indicated that sessile, dome-shaped yak placentomes seemed to have a relatively complex villous-crypt architecture pattern. There was a straight maternal plate beneath the placentome. Plentiful uterine glands and a dense cellular layer were present in the endometrium lamina propria close to the maternal plate. Trophoblast giant cells appeared to have similar ultrastructure features to these in other ruminants, including abundant mitochondria, an extensive array of rough endoplasmic reticulum, advanced Golgi complex and many specific secretory granules. Trophoblast giant cells could also secrete neutral and acid glycoconjugates. Furthermore, numerous glycoconjugates were distributed in the connective zones between mononuclear trophoblast cells and crypt epithelial cells as well as in maternal connective tissues. Mononucleate trophoblast cells which had abundant microvilli that interdigitated with the corresponding microvilli arising from the crypt epithelial cells, had numerous mitochondria and vesicles,but did not exist glycoconjugates.