Comparison of different cryopreservation techniques: higher survival and implantation rate of frozen-thawed mouse pronuclear embryos in the presence of beta-mercaptoethanol in post-thaw culture.

The objective of this study was to investigate the effects of beta-mercaptoethanol (β-ME) on post-thaw embryo developmental competence and implantation rate of mouse pronuclear (PN) embryos that were cryopreserved after slow freezing, solid surface vitrification (SSV) or open-pulled straw (OPS) vitrification methods. Mouse PN embryos were cryopreserved by using slow freezing, SSV and OPS methods. After cryopreservation, freeze-thawed PN embryos were cultured up to blastocyst stage in a defined medium supplemented without or with 50 μM β-ME. The blastocyst formation rate of embryos that were cryopreserved by slow freezing method (40.0%) or vitrified by OPS method (18.3%) were lower than those vitrified by SSV method (55.6%) and fresh embryos (61.9%) in the absence of 50 β-ME in the culture media (p < 0.05). The blastocyst formation rate of embryos that were cryopreserved by slow freezing method (53.1%) or by OPS method (41.9%) were lower than those vitrified by SSV method (79.5%) and that of fresh (85.7%) in the presence of β-ME in the culture media (p < 0.05). The embryos transfer results revealed that the implantation rate of blastocyst derived from mouse PN embryos vitrified by SSV method (31.9% vs 51.2%) was similar to that of the control (39.0% vs 52.5%), but higher than those cryopreserved by slow freezing (28.2% vs 52.0%) and by OPS method (0.0% vs 51.2%) (p < 0.05). In conclusion, supplementation of β-ME in an in vitro culture medium was shown to increase survival of embryo development and implantation rate of frozen-thawed mouse PN embryos after different cryopreservation protocols.