B, Transmission electron microscopic analyses (TEM) showed that the uterine epithelium surrounding the embryo disappears and the trophoblast contacts directly with the stroma at 2000h on day 5 in Rb1f/f mice, while the uterine epithelium is persistent and the embryo does not attach to the stroma in Rb1d/d mice. Scale bar = 10µm; red dotted line, stroma; green dotted line, luminal epithelium; blue dotted line, trophoblast. 