Effect of oviduct epithelial cells on the fertilization and development of sheep oocytes in vitro

Abstract

The study examined whether co-culture with oviductal epithelial cells was of benefit to ovine in vitro fertilization (IVF) and embryo culture procedures utilizing a well characterized culture system based on a synthetic oviductal fluid medium (SOFM) supplemented with serum in a 90% N2, 5% O2, 5% CO2, atmosphere at 38.6°C. Two experiments were carried out. In Experiment 1, comparison was made between the frequency of fertilization and development of in vitro matured (IVM) oocytes cultured in the absence (Group 1) or presence of oviductal cells for a 24 h (Group 2), 48 h (Group 3) or 96 h (Group 4) period post insemination. In Experiment 2, comparison was made between the development of IVM oocytes fertilized and cultured in vitro for 7.5 days in the absence or presence of oviductal cells with IVM oocytes which had been fertilized in vitro for 20 h in the presence of oviductal cells and then transferred to the oviducts of a recipient ewe, 30 h post oestrus, for a 6.5 day period of in vivo culture. Similar rates of fertilization (54-58%) and blastocyst development from cleaving zygotes (48-69%) were achieved in both experiments in vitro with no evident benefit of including oviductal cells. In fact, fewer (P = 0.02) blastocysts developed from cleaved embryos when co-cultured for the 96 h period (Group 4). Whilst the blastocyst development rates obtained in vitro (45-58%) were similar to, or higher than (P = 0.03), those obtained in vivo (43%), more than 50% of in vitro cultured embryos in both experiments showed evidence of fragmentation and/or irregular cleavage as well as a lack of firm compaction at the morula stage. Also the blastocysts that had not hatched, or hatched by 7.5 days of in vitro culture had significantly fewer cells than those cultured in vivo (P < 0.003). The results confirm that SOFM supplemented with serum can support the fertilization and development of ovine oocytes to the blastocyst stage in vitro, but that development is compromised compared with that obtained in vivo and that these defects were not offset by including oviductal cells in the culture media. However, it should be noted that the composition of the medium and gaseous atmosphere developed for the IVF embryo culture procedures are recognized as being suboptimal to the maintenance of the viability of somatic cells, highlighting the difficulties of selecting culture conditions suited for both embryonic and somatic cells development, a primary requisite for realizing the potential beneficial effects of co-culture on embryo viability. © 1994.