Co‐culture of rabbit 2‐Cell embryos with rabbit oviduct epithelial cells and other somatic cells

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Abstract
Rabbit 2‐cell embryos were co‐cultured in Basal Synthetic Medium II + 10% fetal bovine serum with one of the following: primary cultures of rabbit oviduct epithelial cells (ROEC), a rabbit kidney epithelioid cell line (RK13), a rabbit epidermal epithelioid cell line (Sf1), or a rabbit skin fibroblast‐like cell line (RAB9). Embryos cultured in medium alone served as controls. After 4 d of culture at 39°C in 5% CO2in air, 77–93% of the rabbit embryos which were co‐cultured with somatic cells had reached the blastocyst stage, and 60–76% were hatching through their zonae pellucidae. These percentages, however, were not significantly different (P>.05) from those of embryos in medium alone, of which 90% had reached the blastocyst stage and 83% were hatching. Mean intrazonal embryo diameters also did not differ significantly among treatments (239–302 μm). Bovine 1–8‐cell embryos were also co‐cultured with ROEC. This stimulated 60% of these embryos to develop beyond the so‐called “16‐cell block” in vitro, whereas 0% of the embryos cultured in medium alone developed past this block. Evaluation of the ROEC cultures by light microscopy, immunocytochemistry, and gel electrophoretic analysis of conditioned medium, together with the positive results with bovine embryos, indicate that the ROEC culture partially simulates oviductal conditions in vivo. Therefore, our results suggest that oviduct epithelial cells may play a less pivotal role in regulating early development in the rabbit than in the cow. However, other factors besides those provided by the ROEC cultures must also be important for optimal development, as both rabbit and bovine embryos develop more slowly in co‐culture than in vivo.