Effect of the removal of cumulus cells on the nuclear maturation, fertilization and development of porcine oocytes

The present study was conducted to investigate the effects of attachment of cumulus cells to porcine oocytes during the process of maturation and fertilization on the nuclear maturation, fertilization and subsequent development after in vitro fertilization (IVF). In the first experiment, the cumulus cells were removed from cumulus-oocyte complexes (COCs) at 0, 24 and 42 h after the onset of maturation culture and were then cultured until reaching 42 h of cultivation. In the second experiment, COCs were denuded as described in the first experiment, then fertilized and cultured for 7 days. As a control, cumulus cells were allowed to maintain attachment to the oocytes until the end of IVF. The proportion of oocytes reaching metaphase II significantly increased with the delay in the removal treatment of cumulus cells. The proportion of normal fertilization gradually increased with delay in the removal treatment of cumulus cells from COCs until the end of IVF. However, no significant difference in the proportion of normal fertilization was found between the 42-h and control groups. The removal treatment of cumulus cells in the 0- and 24-h group significantly (p < 0.05) decreased the proportion of cleaved embryos when compared with the control, and none of them developed to the blastocyst stage. The proportion of development to the blastocyst stage was significantly higher (p < 0.05) in the control group than in the 42-h group (18.1% vs 12.4%; p < 0.05). The present study indicates that the attachment of cumulus cells to the oocyte during maturation and fertilization is important to support oocyte nuclear maturation, fertilization and subsequent embryo development. Particularly, the attachment of cumulus cells to the oocyte during IVF promotes embryonic development.