The effect of cooling and hypertonic exposure on murine oocyte function, fertilization, and development

Area of Science:

• Reproductive Biology
• Cryobiology
• Developmental Biology

Background:

• Cryopreservation involves multiple steps: cryoprotectant addition, cooling, storage, rewarming, and removal.
• Understanding the impact of individual steps is crucial for optimizing oocyte cryopreservation protocols.
• Mouse oocytes are a model system for studying reproductive cell cryopreservation.

Purpose of the Study:

• To differentiate the effects of specific cryopreservation procedures on mouse oocyte viability.
• To assess the impact of temperature, media tonicity, and cooling rates on fertilization and embryonic development.

Main Methods:

• Mouse oocytes were subjected to various conditions: isotonic/hypertonic media at 37°C, slow/rapid cooling to 0°C, and exposure to cryoprotectants (glycerol, dimethyl sulfoxide).
• Fertilization rates and subsequent development to hatching blastocyst were assessed for each experimental group.
• Control oocytes underwent standard in vitro fertilization and culture.

Main Results:

• Exposure to isotonic or hypertonic media at 37°C did not significantly affect fertilization or development.
• Rapid cooling to 0°C reduced fertilization rates, especially when combined with hypertonic solutions.
• Cryoprotectant exposure (glycerol, DMSO) reduced fertilization and development, but subsequent cooling or hypertonic exposure had no additional negative impact.

Conclusions:

• Hypertonic solutions and rapid cooling are detrimental to mouse oocyte cryopreservation, significantly reducing fertilization and development.
• Cryoprotectant addition is a critical step, and its effects appear to dominate over subsequent cooling or tonicity challenges.
• Optimizing cooling rates and maintaining isotonic conditions are essential for improving cryopreservation success in oocytes.