The mechanism of action of coculture on embryo development in the mouse model: direct embryo-to-cell contact and the removal of deleterious components

Objective: To elucidate the mechanism for the mode of action of coculture b y the use of a coculture system for mouse one-cell embryos with human ovidu ctal epithelial cells. Design: Prospective, controlled in vitro experimental study. Setting: Academic research laboratory. Animal(s): Female ICR strain mice aged between 6 and 8 weeks. Intervention(s): Flushed one-cell embryos were cultured in human tubal flui d medium alone (control), in coculture system with human oviductal cells, i n five kinds of conditioned media, and in a contactless coculture system us ing a cell-culture insert. Main Outcome Measure(s): The percentage of the embryos developed to hatchin g blastocyst stage and the level of superoxide anion in the supernatant fro m each culture condition. Result(s): The rates of embryo development to the hatching blastocyst stage were significantly higher in the coculture group (43%) than in the control group (none) (P < .05). The embryo development rate in the control group w as similar to that of the embryos in the five kinds of conditioned media. T he effects of coculture on embryo development disappeared in the contactles s coculture group. The level of superoxide anion was significantly reduced in the coculture group compared to the control group. Conclusion(s): The present coculture system overcomes the two-cell block in vitro and improves the embryo development. The beneficial effect may be a result of direct cell-to-cell contact between the embryo and helper cells a nd the removal of deleterious components from medium, rather than a result of embryotrophic factors. (C) 2001 by American Society for Reproductive Med icine.