TRANSFER OF NUCLEI FROM 8-CELL STAGE MOUSE EMBRYOS FOLLOWING USE OF NOCODAZOLE TO CONTROL THE CELL-CYCLE

Mouse 2-, 4-, 8-, and 16-cell embryos were exposed to nocodazole in M1 6 culture medium. The effect of different concentrations and exposure times on the efficiency of cell cycle synchronization and the developm ent of the treated embyros after release from the drug was determined. The minimum effective concentration (>95% of arrested nuclei) for 4-, 8-, and 16-cell embryos was 5 mu M nocodazole. The effect upon subseq uent development of mouse embryos depended upon both the stage of deve lopment of the embryo at treatment (P < 0.001) and the length of expos ure to nocodazole (P < 0.001). Exposure to any concentration of nocoda zole within the range 2.5-10 mu M for 12 hr caused a reduction in the proportion of embryos that formed blastocysts. As the period of exposu re to 5 mu M nocodazole increased from 12 to 24 hr, the proportion of embryos developing to the blastocyst stage decreased. The lower propor tion of embyros developing to the blastocyst stage and to term (P < 0. 01) suggests that the more advanced stages were more susceptible to da mage as a result of exposure to nocodazole. The rate of development of 4-cell embryos to blastocysts was not affected when an exposure time of 9 hr was used. Together these results show that it is possible to u se nocodazole to arrest mouse embryonic cells in mitosis but that it i s not appropriate to culture the embryos in the presence of this drug for prolonged periods. Individual blastomeres completed mitosis at 60- 90 min and started DNA synthesis at 120-150 min after release from noc odazole. Nuclei from blastomeres thus synchronized were used to conduc t studies on the effect of the cell cycle on nuclear transfer. A signf icant effect was found. When nuclei from 8-cell embryos in G1 or S-pha se were used as nuclei donors, development to blastocyst was respectiv ely 27% and none. (C) 1994 Wiley-Liss, Inc.