124 CRYOPRESERVED BOVINE OVIDUCTAL EPITHELIAL CELLS SURVIVAL, GROWTH, AND ABILITY TO SUPPORT EARLY EMBRYO DEVELOPMENT

Abstract

Previous experiments demonstrated that co-culture of bovine embryos with bovine oviducal epithelial cells (BOEC) improved blastocyst rate and quality (Cordova et al. 2014). However, the use of primary cell support for improving embryo development in vitro may introduce a higher variability of the results between different BOEC batches used, as well as sanitary risks. The use of well-controlled large batches of frozen BOEC may help to solve these problems. Therefore, the aim of the present study was to characterise the survival and functionality of frozen-thawed BOEC. Bovine oviducts attached to ovaries showing recent ovulation were collected at a local slaughterhouse during 4 replicates (3 oviducts per replicate). Epithelial cells were expelled by gentle squeezing and washed 3 times. Half of the cell pellet was diluted 100-fold in culture medium (TCM199 + 10% FCS) for culture of fresh cells. The other half was diluted 10-fold in cell freezing medium (TCM199 + 20% FCS + 10% dimethyl sulfoxide), allowed to equilibrate in this medium for 10 min, and frozen at –80°C in a container filled with isopropyl alcohol. After 4 h, the tubes were transferred into LN for at least 1 h. The tubes were then thawed (5 min in 37°C water bath), diluted 1 : 1 in cell culture medium, and centrifuged for 10 min at 100 × g. The pellet was then diluted 100× in cell culture medium. Fresh or frozen-thawed cells were seeded in 4-well NUNC plates for 7 days at 38.8°C in a humidified atmosphere with 5% CO₂ in air. The medium was renewed every 48 h, and the viability of cells was assessed by calcein-AM and ethidium homodimer labelling. After 7 days of culture, the medium was replaced by SOF medium + 5% FCS, and bovine in vitro-produced zygotes were added the day after and co-cultured for 8 days at 38.8°C in a humidified atmosphere with 5% CO₂ in air to evaluate embryo development. Half of the medium was renewed every 48 h. Frozen-thawed cells showed the same viability than fresh ones at Days 0 and 7 of culture and reached confluence at the same time (Day 7). Development results are shown in Table 1. Frozen and fresh cells support early embryo development at the same rate. In conclusion, the present study showed that BOEC frozen on the day of collection are equivalent to fresh BOEC in regards to their survival and proliferation and their ability to support early embryo development. At collection, the cells may face stresses that are just as considerable as freezing/thawing (temperature shock, scrapping, change of environment). This may explain why they are not affected by freezing than at collection. The differentiation status of these cells is now under analysis by immunocytochemistry.

Table 1.  Cleavage rate and blastocyst rate in 3 different types of culture systems