The Effects of Vero Cell Coculture on Mouse Oocyte Maturation and Embryo Development in Vitro

Assisted reproductive technology(ART) have contributed significantly to alleviating subfer-tility in the childless couple. In spite of the many advances in the field of ART, the pregnancy and take-home baby rates for in vitro fertilization(IVF) have been very poor. In order to overcome these problems, a variety of coculture systems has been devised. Vero cells, derived from African green monkey kidney, were selected because kidney and genital tract have a common embryonic origin. In addition, these cells are safe for coculture with embryos : they are highly controlled for viruses and other contaminants because they are used for vaccine production. Several investigators showed that cocultureing human embryos with Vero cells in vitro resulted in an improvement of embryo development. However, they did not observe the same results using mouse oocytes and embryos. We thus designed a series of experiments to demonstrate whether or not Vero cells do indeed enhance mouse oocyte maturation and embryo development. In this experiment, Vero cell does not allow the mouse immature oocytes to be enhanced maturation rate in vitro.

To study the 'In-Vitro 2-cell Block' in mouse embryo, we have cocultured ICR one-cell mouse embryos with Vero cell in different medium. In Ham's F-10 the mouse embryos arrested their development prior to 4-cell stage(control 76.7%;coculture 75.0%). In contrast, the coculturing mouse embryos revealed enhanced development(control 0%;coculture 22.8%) in human tubal fluid(HTF) only in late embryonic stages(hatching).

On the other hand, the degree of blastomere fragmentation exhibited a reverse trend to that of the developmental capacity. Embryos from coculture groups(Ham's F-10 & HTF) showed some fragmentation(0% & 4.2%) while 13.3% and 14.3% of the embryos in control groups(Ham's F-10 & HTF) were severely fragmented(P<0.05). Thus the use of coculture systems appears to be dependent on the type of medium used as a support.

The development rate of late 2-cell mouse embryos in Vero cell coculture was no significant differences until blastocyst stage but improved at late developmental stage(control 42.1% ; conculture 70.7%). Thus the Vero cell coculture system was shown to increase the hatching rate of mouse embryos.