EVALUATION OF VERO CELL COCULTURE SYSTEM FOR MOUSE EMBRYOS IN VARIOUS MEDIA

Our objective was to evaluate and compare the efficacy and mechanisms of co-culturing mouse embryos with Vero cells in both Dulbecco's modified Eagle's medium/Ham's F12 (DMEM/F12) and human tubal fluid (HTF) culture medium. Two-cell CB6F1 mouse embryos were cultured either in the presence of Vero cells (group A) or in culture medium alone (group B). In DMEM/F12 significantly more morulae developed in group A than in group B on day 3 (91 versus 23%; P < 0.01). In contrast, the mouse embryos grew rapidly in HTF and significant differences were noted only in later embryonic stages (on day 5; 86% and 50%, P < 0.01 of group A and B respectively, hatching or hatched). Similar experiments using DF1 and ICR mouse strains also revealed enhanced embryo development in the presence of Vero cells. To determine whether the embryo-enhancing effects of Vero cells were due to the removal of toxins or to the secretion of embryotrophic factors, ICR mouse embryos were cultured in fresh media with cells (group A), without cells (group B) and in cell-free conditions using cell-conditioned media which were obtained in the presence (group C) or absence (group D) of embryos. These results demonstrated that completion of hatching was highest (52%; P < 0.01) in group A after 6 days in culture. There were no significant differences between groups B, C and D (rates of total hatching 18, 17 and 17%, respectively). It is concluded that Vero cells improve the development of mouse embryos and this is likely to be due to removal of substances inhibitory to development. The beneficial effects of Vero cells in HTF in later developmental stages may be due to the removal of toxins resulting from media degradation.