Strain differences in early mouse embryo development in vitro: role of the nucleus

Mouse embryos of many strains are blocked in development at the two-cell stage when placed in culture at the one-cell stage. If, however, they are placed in culture at the two-cell stage, they develop to blastocysts at a high rate. We investigated the transcriptional and translational systems in blocked embryos by assaying enzymatic activity of the protein product of an injected gene and found these systems to be functioning normally. The role of the nucleus was investigated by reciprocal nuclear transplants between blocked and nonblocked embryos. The results indicate that the source of the nucleus was of equal importance to that of the cytoplasm for the successful development of embryos cultured from the one-cell stage. When cultured from the two-cell stage, however, the nucleus was solely responsible for strain differences in culture rates.