REDUCING THE AMOUNT OF CYTOPLASM AVAILABLE FOR EARLY EMBRYONIC-DEVELOPMENT DECREASES THE QUALITY BUT NOT QUANTITY OF EMBRYOS PRODUCED BY IN-VITRO FERTILIZATION AND NUCLEAR TRANSPLANTATION

The effect of reducing the amount of cytoplasm available for early emb ryonic development was investigated in embryos produced by in vitro fe rtilization (IVF) and nuclear transplantation. In Experiment 1, approx imately 1/2 or 1/20 of the cytoplasm was removed from bovine embryos a t the pronuclear-stage of development. The percentage of embryos devel oping to the compact morula or blastocyst stage was significantly high er in non-manipulated controls (26%) than in embryos with 1/20 of the cytoplasm removed (16%), and those with 1/2 of the cytoplasm removed ( 10%; P <0.05). There was also a significant difference in the average number of cells between blastocysts in which 1/20 of their cytoplasm w as removed (67), those with 1/2 of their cytoplasm removed (55), and n on-manipulated controls (77; P <0.05). In Experiment 2, nuclear transf er embryos were produced in which approximately 1/2 or 1/20 of the cyt oplasm was removed during oocyte enucleation. The percentage of embryo s developing to the blastocyst stage was 17% for both groups of nuclea r transfer embryos compared to 44% for control embryos (P <0.05). The mean number of cells in blastocysts produced by nuclear transfer in wh ich 1/20 of the cytoplasm was removed during oocyte enucleation (61) w as no different than that in control embryos (66), but significantly h igher than the mean number of cells in blastocysts produced by nuclear transfer in which 1/2 of the cytoplasm was removed (42; P <0.05). The re was no indication that altering the amount of cytoplasm available f or early embryonic development of IVF embryos affected the timing of d ifferentiation events, including those of embryo compaction and blasto cyst formation.