In vitro viability and ultrastructural changes in bovine oocytes treated with a vitrification solution

Area of Science:

• Reproductive Biology
• Cryobiology
• Oocyte Biology

Background:

• Cryoprotective agents are essential for preserving oocytes.
• Understanding cryoprotectant effects on oocyte ultrastructure and function is crucial for improving assisted reproductive technologies.
• Bovine oocyte cryopreservation protocols require optimization to maintain developmental potential.

Purpose of the Study:

• To evaluate the impact of a concentrated cryoprotectant solution (DAP213) on bovine oocyte viability and ultrastructure.
• To compare the sensitivity of germinal vesicle (GV) stage oocytes versus in vitro matured (IVM) oocytes to DAP213 exposure.
• To elucidate the role of cortical granule release in cryoprotectant-induced damage.

Main Methods:

• Bovine oocytes at GV or IVM stages were exposed to DAP213 for 1.5 or 5 minutes.
• Oocyte viability was assessed through in vitro fertilization (IVF) and subsequent culture to blastocysts.
• Transmission electron microscopy (TEM) was used to examine ultrastructural changes, including cortical granule exocytosis.

Main Results:

• DAP213 induced ultrastructural alterations, including microvilli and mitochondrial damage, and premature cortical granule release.
• IVM oocytes exposed for 5 minutes showed reduced IVF rates and increased cortical granule exocytosis.
• GV oocytes exposed for 5 minutes exhibited increased polyspermy, reduced cleavage, and blastocyst formation rates, with more organelle alterations.

Conclusions:

• Cortical granule kinetics is a key factor influencing the fertilizability of bovine oocytes treated with cryoprotectants.
• Germinal vesicle (GV) stage bovine oocytes are more susceptible to cryoprotectant damage than in vitro matured (IVM) oocytes.
• Exposure duration and oocyte maturation stage significantly influence the detrimental effects of cryoprotectants on bovine oocyte quality and developmental competence.