Intercellular Contacts Between the Embryonic or Extraembryonic Ectoderm and the Primitive Endoderm in Rat Egg Cylinders Prior to the Formation of Primitive Streak

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Abstract
In pre-primitive-streak stage rat egg cylinders, the embryonic and extraembryonic ectodermal cells projected cytoplasmic protrusions through gaps in the basal lamina and formed intimate cell-to-cell contact with the primitive endodermal cells. The 70 .ANG. microfilaments were considered to participate in the production of these cytoplasmic protrusions. Direct cell contact mediated by adherent junctions was occasionally found between the embryonic or extraembryonic ectodermal cells and the primitive endodermal cells. These cell-to-cell contacts may play a role in the supporting effect of primitive endodermal cells in the maintenance of cellular organization of the ectodermal cells, or in the facilitation of transport of nutritive materials from the primitive endodermal cells to both types of ectodermal cells.