PURPOSE: Although the hatching of embryos is an important phenomenon, the mechanism of hatching remains controversial. Therefore, we attempted to develop a new coculture system with human placental cells to investigate the hatching of mouse embryos. RESULTS: In our new system there was no difference in development from the two-cell stage to blastocysts between embryos cultured with a T6 medium and embryos cocultured with human placental cells at 1 x 10(5), 5 x 10(5), and 1 x 10(6) cells/ml. However, the hatching-rate cell number increased significantly in embryos cocultured with placental cells compared to embryos cultured without placental cells. [3H]Thymidine uptake did not show any significant difference from the beginning of in vitro culture to the hatching stage between the coculture group and the control group. Nevertheless, the [3H]uridine uptake was significantly different in the two groups, measuring 2167 +/- 532 cpm/10 embryos in the coculture group and 804 +/- 86 cpm/10 embryos in the control group at 114 hr after human chorionic gonadotropin injection (P < 0.01). CONCLUSION: These results therefore seem to indicate that the hatching of blastocysts depends on the protein synthesis of the embryos and not on DNA duplications.
PURPOSE: Although the hatching of embryos is an important phenomenon, the mechanism of hatching remains controversial. Therefore, we attempted to develop a new coculture system with human placental cells to investigate the hatching of mouse embryos. RESULTS: In our new system there was no difference in development from the two-cell stage to blastocysts between embryos cultured with a T6 medium and embryos cocultured with human placental cells at 1 x 10(5), 5 x 10(5), and 1 x 10(6) cells/ml. However, the hatching-rate cell number increased significantly in embryos cocultured with placental cells compared to embryos cultured without placental cells. [3H]Thymidine uptake did not show any significant difference from the beginning of in vitro culture to the hatching stage between the coculture group and the control group. Nevertheless, the [3H]uridine uptake was significantly different in the two groups, measuring 2167 +/- 532 cpm/10 embryos in the coculture group and 804 +/- 86 cpm/10 embryos in the control group at 114 hr after human chorionic gonadotropin injection (P < 0.01). CONCLUSION: These results therefore seem to indicate that the hatching of blastocysts depends on the protein synthesis of the embryos and not on DNA duplications.