210 CO-CULTURE WITH AUTOLOGOUS CUMULUS CELLS SUPPORTS THE INDIVIDUAL DEVELOPMENT OF SINGLY IN VITRO-MATURED AND FERTILIZED BOVINE OOCYTES

Abstract

The ability to produce embryos singly in vitro (in vitro production, IVP) would be a useful tool for many purposes. Without the interfering effects of other developing or degenerating oocytes or embryos, such an individual IVP system is the tool of choice for studies on oocyte quality and oocyte–embryo metabolism. Unfortunately, individual IVP in most cases leads to unsatisfactorily low blastocyst rates. Earlier work showed that individual culture of zygotes on a cumulus cell (CC) monolayer resulted in comparable numbers of good-quality embryos, as obtained following regular group culture (Goovaerts et al. 2009 Theriogenology 71, 729–738). However, co-culture with somatic cells is often criticised because of the undefined culture conditions and for sanitary reasons. In the cited study, CC for monolayer production were obtained from a different batch of ovaries. Our specific aim was to use CC from the zygote itself (autologous CC). Grade I COC (n = 660) were collected from slaughterhouse ovaries and randomly assigned to 2 treatments (5 replicates): a completely individual ‘single-oocyte’ IVP protocol, or routine group IVP as a control. Individual maturation (TCM-199 + 20% serum) and fertilization were performed in 20-μL droplets under oil in 24-well plates. Subsequently, each zygote was stripped and cultured in 20 μL of medium (SOF + 5% serum, 90% N₂, 5% CO₂, 5% O₂), to which the autologous stripped CC were added. Group maturation and fertilization were carried out per 100 COC in 500 μL, whereas group culture was performed per 25 zygotes in 50-μL droplets under oil. Cleavage, blastocyst, and hatching rates were determined 2, 8, and 10 days post-fertilization, respectively. Possible effects of the individual and group cultures were evaluated with binary logistic regression (SPSS 15.0, SPSS Inc., Chicago, IL). No interactions between replicate and treatment were found (P > 0.05). Although a blastocyst rate of 15.1% was obtained using single IVP, the general efficacy of the single-embryo production system was lower when compared with group culture (Table 1). In conclusion, although developmental competence was impaired using individual IVP, co-culture with autologous cumulus cells can be useful in specific experimental setups in which the influence of other oocytes or embryos or heterologous somatic cells is unacceptable.

Table 1.  Cleavage, blastocyst, and hatching rates after individual and group in vitro production (IVP)