Ultrastructural study of the mouse antimesometrial decidua.

The ultrastructure of mouse antimesometrial decidual cells was analyzed during the development of the decidua between days 5 and 8 of pregnancy. The first decidual cells, appearing on the 5th day, are polygonal with rounded nuclei and prominent nucleoli; free ribosomes predominate in the cytoplasm. On the 6th to the 8th days the cytoplasm of these cells is typically that of cells actively engaged in macromolecular synthesis. Large numbers of granular and agranular endoplasmic reticulum cisternae are present in addition to well-developed Golgi complexes, mitochondria and lysosomes. Many bundles of microfilaments and lipid droplets occur during this period. An intense accumulation of autophagosomes and lysosomes with very heterogeneous content was noted on the 7th and especially the 8th days. The presence of these organelles is an indication that involution of this part of the decidua has begun.