E, Immunofluorescence of MFG-E8, a marker of programmed cell death, showed that MFG-E8 is not expressed at the implantation sites of Rb1f/f mice at 0900h on day 5 and Rb1d/d mice at 0900h and 2000h on day 5, but is expressed at the implantation sites of Rb1f/f mice at 2000h on day 5. Scale bar = 100μm; blue signal, nuclei stained by DAPI; yellow signal, MFG-E8; arrowhead, embryo. 