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

Abstract

Objective: To elucidate the mechanism for the mode of action of coculture by the use of a coculture system for mouse one-cell embryos with human oviductal 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 fluid medium alone (control), in coculture system with human oviductal cells, in five kinds of conditioned media, and in a contactless coculture system using a cell-culture insert. Main Outcome Measure(s): The percentage of the embryos developed to hatching blastocyst stage and the level of superoxide anion in the supernatant from 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 was similar to that of the embryos in the five kinds of conditioned media. The effects of coculture on embryo development disappeared in the contactless 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 and the removal of deleterious components from medium, rather than a result of embryotrophic factors.