EFFECTS OF THE REDUCTION OF CYTOPLASM OF MOUSE 2-CELL EMBRYOS ON BLASTOCELE FORMATION TIMING AND DEVELOPMENTAL ABILITY IN-VITRO AND IN-VIVO

Experiments were conducted to test the hypothesis that the nucleo/cyto plasmic ratio of mouse embryos determines the time of blastocele forma tion. Half the volume of 2-cell stage embryos was removed from each bl astomere by micropipette to alter the nucleo/cytoplasmic ratio. Reduce d embryos chose nucleo/cytoplasmic ratio increased and non-treated con trol embryos were cultured in vitro to compare the timing of division to the 4-cell stage and blastocele formation. Reduced 2-cell embryos f ormed blastoceles significantly earlier than the controls(49.0+/-2.9 v s 52.2+/-6 h) and with fewer cells, although division into the 4-cell stage was significantly delayed(11.4+/-4.4 vs 9.0+/-2.4 h). The cell n umber of blastocysts 70 h after treatment and developmental ability of blastocysts after transfer to pseudopregnant recipients were the same for the reduced and control groups. The present study indicates that the nucleo/cytoplasmic ratio of embryos may possibly be an important f actor that determines the time of blastocele formation.