In oestrus stage, canine oocytes surrounded by cumulus cells undergo maturation in oviduct for 3 days after ovulation. We hypothesised that canine cumulus cells (cCC) and canine oviduct cells (cOC) in oestrus stage might affect the maturation of oocyte and embryo development. Therefore, the present study was aimed to compare the effects of cCC and cOC co-culture system on oocyte in vitro maturation and embryo in vitro development. cCC were separated from cumulus‐oocyte complex (COC) in ovary from bitches in oestrus phase. cOC were collected from oviduct flushing of bitches in oestrus phase. Both cCC and cOC were cultured and cryopreserved until use for co-culture. In the first experiment, the effect of co-culture using cCC and cOC on porcine oocyte in vitro maturation (IVM) were investigated. The porcine COC were randomly cultured in different co-culture groups as follows: 1) co-culturing with cCC for 42 h, 2) co-culturing with cOC for 42 h, and 3) culturing in absence of cCC or cOC. After IVM, extrusion of the first polar body was observed under a microscope. In the second experiment, the matured oocytes with the first polar body derived from each group were activated with electrical stimulus. Parthenotes were cultured in porcine zygote medium-5 (PZM-5) for 7 days at 39°C, 5% CO2 and O2 in a humidified atmosphere. The embryo developmental competence was estimated by assessing the in vitro development under microscope. The third experiment was to evaluate the reactive oxygen species (ROS) levels in each supernatant medium obtained from cCC and cOC co-culture group after IVM using a OxiselectTM ROS ELISA Assay kit. Last, analysis of genes (MAPK1/3, SMAD2/3, GDF9 and BMP15) expression in cCC and cOC co-cultured with porcine COC using real-time PCR is in progress. As results, IVM rate of cOC group (91.19 ± 0.45%) was significantly higher than that of cCC and control group (86.50 ± 0.61% and 79.81 ± 0.82%; P < 0.05). Also, cOC groups expressed the highest efficiency in cleavage rate, blastocyst formation rate, and the total cell number in blastocyst (P < 0.05). In ROS levels, cOC group (555 ± 7.77 nM) were significantly lower than cCC and control groups (596.8 ± 8.52 nM and 657.8 ± 11.34 nM). The present study demonstrated that co-culture with cOC improved the in vitro oocyte maturation and the in vitro development rate of porcine embryos. The ROS level decreased in cOC co-culture would have beneficial influence on oocytes maturation. For further study, we will investigate the relation between gene expression related to oocyte maturation and the co-culture results.
This research was supported by a global PhD Fellowship Program through NRF funded by the Ministry of Education (NRF-20142A1021187), RDA (#PJ010928032015), IPET (#311011–05–4-SB010, #311062–04–3-SB010), Research Institute for Veterinary Science, and the BK21 plus program.
Modification of maturation condition improves oocyte maturation and in vitro development of somatic cell nuclear transfer pig embryos