A Comparison of Blastocyst Formation from One-Cell Mouse Zygotes Following an Aseptic Vitrification System

Abstract

Background: Conventional vitrification techniques have promising results. However, many use an open straw system, requiring the sample to be in direct contact with liquid nitrogen, thereby allowing the potential for contamination. An aseptic (closed) vitrification system offers protection for the sample and prevents contamination.Objective: The purpose of this study was to investigate the survivability and developmental potential of one-cell mouse zygotes after vitrification in either an aseptic or an open system.Materials and Methods: A total of 208 one-cell mouse zygotes were divided into two vitrification groups, either aseptic (AV) or open (OV), and one untreated control group. Standard vitrification media containing an equilibration solution of 7% DMSO with 7% EG and a vitrification solution of 15% DMSO with 15% EG were used for both the AV and the OV groups. The AV group used the high-security vitrification kit (HSV kit; Cryo Bio System, France) which included a capillary tube cut on one end to form a gutter for placing the sample and an outer HSV straw. The HSV straw is heat sealed once the capillary tube is placed inside, to prevent direct exposure of the one-cell mouse zygotes to liquid nitrogen. The OV group used only the capillary tube, so the cells were directly exposed to the liquid nitrogen. After warming, all three groups were cultured in vitro to determine cleavage and blastocyst rates.Results: The developmental rate of the one-cell mouse zygote to a cleaved embryo was 94% (31/33) in the control group, 93% (64/69) in the OV group, and 92% (84/91) in the AV group. Blastocyst formation rate was 81% (25/31) in the control group, 86% (55/64) in the OV group, and 82% (69/84) in the AV group. Statistical analysis by chi-squared found no significant differences between the groups for either cleavage or blastosyct formation rates.Conclusions: This study demonstrated that using an aseptic system can avoid contamination without reducing the rates of survivability and developmental potential of one-cell mouse zygotes. Background: Conventional vitrification techniques have promising results. However, many use an open straw system, requiring the sample to be in direct contact with liquid nitrogen, thereby allowing the potential for contamination. An aseptic (closed) vitrification system offers protection for the sample and prevents contamination. Objective: The purpose of this study was to investigate the survivability and developmental potential of one-cell mouse zygotes after vitrification in either an aseptic or an open system. Materials and Methods: A total of 208 one-cell mouse zygotes were divided into two vitrification groups, either aseptic (AV) or open (OV), and one untreated control group. Standard vitrification media containing an equilibration solution of 7% DMSO with 7% EG and a vitrification solution of 15% DMSO with 15% EG were used for both the AV and the OV groups. The AV group used the high-security vitrification kit (HSV kit; Cryo Bio System, France) which included a capillary tube cut on one end to form a gutter for placing the sample and an outer HSV straw. The HSV straw is heat sealed once the capillary tube is placed inside, to prevent direct exposure of the one-cell mouse zygotes to liquid nitrogen. The OV group used only the capillary tube, so the cells were directly exposed to the liquid nitrogen. After warming, all three groups were cultured in vitro to determine cleavage and blastocyst rates. Results: The developmental rate of the one-cell mouse zygote to a cleaved embryo was 94% (31/33) in the control group, 93% (64/69) in the OV group, and 92% (84/91) in the AV group. Blastocyst formation rate was 81% (25/31) in the control group, 86% (55/64) in the OV group, and 82% (69/84) in the AV group. Statistical analysis by chi-squared found no significant differences between the groups for either cleavage or blastosyct formation rates. Conclusions: This study demonstrated that using an aseptic system can avoid contamination without reducing the rates of survivability and developmental potential of one-cell mouse zygotes.