Beneficial influence of Vero cells on in vitro maturation and fertilization of bovine oocytes

The aim of this study was to examine the effects of Vero cells and other somatic cells on in vitro maturation of bovine oocytes. Both denuded oocytes and oocytes with intact cumuli (COCs) were cultured on monolayer of Vero cells, cumulus cells and granulosa cells. The effect of gonadotropins was investigated after the addition of gonadotropins to the culture medium. The evaluation using analysis of variance revealed that removal of cumulus cells generally reduced the percentage of oocytes completing their maturation in vitro and that this effect could not be overcome by the addition of gonadotropins to the culture medium. However, in individual experiments, when oocytes were co-cultured with different monolayers of somatic cells, Vero cells were able significantly support the maturation of denuded oocytes, and their beneficial effect was further enhanced by the addition of gonadotropins (76 vs 80.9%). We did not observe a similar effect after the co-culture of oocytes with a monolayer of cumulus cells (65.3 and 53%, respectively). Granulosa cell monolayer delayed maturation in the both COCs and denuded oocytes (10.5 and 16.5%, respectively). In vitro fertilization was successful in most of the experimental groups. However, when denuded oocytes were cultured without any somatic cell support, they did not decondense the penetrated sperm head after in vitro fertilization. This study demonstrates that 1) Vero cells beneficially affect the in vitro maturation of bovine oocytes; 2) cumulus cells in the form of monolayer lose their beneficial influence on in vitro maturation of bovine oocytes; and 3) granulosa cells and FSH and LH alone (without somatic cells) do not show positive effects on in vitro maturation of bovine oocytes.