256 SYNERGISTIC EFFECT ON EMBRYO DEVELOPMENT AND EMBRYO QUALITY WHEN BOVINE DENUDED OOCYTES ARE CO-CULTURED WITH CUMULUS–OOCYTE COMPLEXES DURING IN VITRO MATURATION

Abstract

The oocyte and its surrounding somatic cells are metabolically coupled to each other through gap junctions. This phenomenon allows intercellular communication and transfer of different low-molecular-weight substrates between the cells necessary for oocyte growth. The oocyte itself regulates the cumulus cell microenvironment through oocyte-secreted factors. The development competence of the bovine oocytes is increased when denuded oocytes (DO) are co-cultured with cumulus–oocyte complexes (COC) during in vitro maturation (IVM). However, the fate of the DO, which are usually discarded after IVM, has not been determined. The present study aimed to investigate whether there is a synergistic effect of co-culturing COC and DO during IVM. We performed 3 IVM schemes: 1) COC and DO co-culture, with 12 COC and 60 DO; 2) COC control, with 12 COC; and 3) DO control, with 60 DO in 120-μL drop of TCM-199 for 22 to 24 h. Following IVM, IVF and in vitro culture were separately performed for the COC (COC co-culture) and DO (DO co-culture) from the IVM co-culture group. In vitro fertilization and in vitro culture (modified CR1aa) were done in 60-μL drops. Embryos were cultured at 38.5°C and 5% CO₂ in air. Cleavage and blastocyst rates were checked at Day 3 and 8 from IVF on total COC/DO placed in IVM drop. Day 8 blastocysts were used for TUNEL staining using In Situ Cell Death Detection Kit (Roche, Budapest, Hungary). Data were analysed by one-way ANOVA, and significant differences among groups were tested by DMRT. Compared with the respective control treatments, co-culture has no effect on cleavage rates of COC and DO (see Table 1). However, blastocyst rates and total cell numbers of blastocysts were increased in COC co-culture and DO co-culture group compared with their respective control groups (see Table 1). Co-culture had no effect on apoptosis of blastocysts. These data show that co-culture of COC and DO improved developmental competence and quality of embryos from the COC co-culture and DO co-culture group.

Table 1.  Development competence and blastocyst quality of intact and denuded bovine oocytes