Cleavage rate of diandric triploid mouse embryos during the preimplantation period

The postimplantation development of human and animal triploid embryos is well documented, but there is little informative data on their preimplantation development. An analysis of cell number at appropriate times during this period and thus their cleavage rate would give an indication of the potential triploids have for further development and may explain some problems associated with their postimplantation development. To rule out any effects of technical procedures on cleavage rate, appropriate controls were used. Diandric triploid embryos were produced using standard micromanipulatory techniques, which involved the injection of a male pronucleus into a recipient one‐cell‐stage embryo. The karyoplast was fused to the cytoplasm by electrofusion, and the resulting tripronucleate diandric triploid embryos were transferred to appropriate pseudopregnant recipients. At specific times after the transfer, the embryos were recovered and cell numbers established. The results were plotted and regression lines drawn. Three controls were used (1) micromanipulated diploid embryos from which the male pronucleus had been removed and immediately reinserted and fused to restore diploidy, (2) diploid embryos that had been briefly incubated in cytochalasin D and colcemid to find out the effects these agents had on development, and (3) diploid embryos that had been isolated and briefly incubated in tissue culture medium. All embryos were subsequently transferred to recipients. After isolation at specific times during the preimplantation period, cell numbers were also established and the results plotted. The cell doubling time of the diandric triploid embryos was 13.55 hr (± 1.25), and this was not significantly different from the various controls. The cell doubling time of (1) the micromanipulated controls was 12.12 hr (± 1.16), (2) the control embyros incubated in cytoskeletal inhibitors 10.87 hr (± 0.75), and (3) the group that was briefly incubated in tissue culture 12.43 hr (± 0.74). There was no significant effect of manipulation or incubation in cytoskeletal inhibitors on cleavage rate. Our findings indicate that triploid embryos divide at the same rate as diploid embryos during the preimplantation period.