Studies of the developmental potential of 4‐ and 8‐cell stage mouse blastomeres

Abstract The object of this study was to assess the full developmental potential of all the blastomeres in 4‐cell and 8‐cell stage mouse embryos. Isolated blastomeres at these stages have limited developmental powers, and in order to follow their development into the postimplantation period a method of combining each blastomere into a chimaeric composite was devised. Preliminary experiments indicated the most favourable genetic combinations and blastomere arrangements. For the 4‐cell stage embryos each individual donor blastomere was combined with genetically distinct blastomeres at the same stage to make a “Quarted” of composite embryos. The occurrence of the donor cell characters in these composites when they were recovered at the tenth day of pregnancy and at term, indicates that each 4‐cell stage blastomere is totipotent and may contribute extensively to a mouse and also to the yolk sac and trophoblast. Eight‐cell stage blastomeres were obtained in pairs, each pair being derived from a particular 4‐cell stage blastomere. The development of the pairs were followed in chimaeric composites. Each blastomere of a pair was found to have the same range of developmental potential. This indicates a lack of segregation of morphogenetic factors and implies totipotency of the 8‐cell stage blastomeres. The relevance of these results to the current theories of blastocyst differentiation is discussed.