The Development of Diploid/Tetraploid Mosaic Mouse Embryos Produced by Electrofusion at the 4-Cell Stage

The developmental ability of diploid / tetraploid mosaic mouse embryos produced by electrofusion at the 4-cell stage was examined in vitro and in vivo. Diploid / tetraploid mosaic embryos amounted to 51.3% of embryos treated. They were cultured for 60 h in BMOC-III medium to examine their development, and 77.8% of them developed to blastocysts. This was about the same rate as in unfused diploid embryos. Compaction of the diploid/tetraploid mosaic embryos started at the 6-cell stage, and the mean number of cells in these blastocysts was about three quarters that in control embryos. These embryos which developed to blastocysts were transferred to the uterus of recipients. By 11.5 days of pregnancy, 90.0% of diploid / tetraploid mosaic embryos had been implanted and 25.9% of them had developed into foe-tuses, but in these foetuses, however, there were no tetraploid cells, and they contributed to only some foetal membranes in 3 out of 9 embryos examined. On the 19th day of pregnancy, two recipients were delivered of seven pups altogether. These pups were morphologically normal and grew to be adult mice. Chromosome preparation of the bone marrow cells showed that all of these mice had only diploid chromosome constitutions. These results suggest that tetraploid cells show poor developmental ability after implantation