Is direct cell-to-cell contact needed to improve embryonic development in co-culture?

In vitro co-culture of embryos and somatic cells is used to obtain well-developed embryos of humans and other species. However, it is not known whether direct cell-to-cell contact is essential to embryonic development. To elucidate this mechanism, we cultured mouse embryos using rabbit oviductal cell as a somatic cell. To avoid the direct contact we used a microporous membrane cell-culture insert. This cell-culture insert permits only the liquid portion of the culture medium to pass through it and was interposed between mouse embryos and cultured rabbit oviductal cells. When mouse embryos were placed on the cultured oviductal cells directly, 52.2% of two-cell-stage embryos developed to the blastocyst stage. In contrast, when the cell-culture insert was interposed between the embryos and the cultured oviductal cells, 50.0% of two-cell-stage embryos developed to that stage. There was no difference between the rate of blastocyst development in co-culture system with and without cell culture insert. Results indicate that oviductal factor (a), rather than a direct contact with oviductal cells, is essential to the enhancement of embryonic development in vitro.