A, In Rb1d/d mice with pre-implantation P4 treatment, the fragmented uterine epithelial cells with the cytoplasmic lipid droplets were engulfed by the trophoblast cells. Scale bar = 2µm. Arrowhead, cytoplasmic fragments engulfed by trophoblast; dotted line circle, lipid droplets in the cytoplasm; tr, trophoblast; le, luminal epithelium; s, stroma; red dotted line, stroma; green dotted line, luminal epithelium; blue dotted line, trophoblast. 