In vitro maturation and transmission electron microscopic observation of horse oocytes after vitrification.

This research study used horse oocytes, or egg cells, to examine the feasibility of their preservation through vitrification. While exposure to the vitrification solution caused some cellular changes, the results suggested that immature horse oocytes can be successfully cryopreserved with minimal disruption to viability.

Research Methodology

• The researchers collected immature oocytes from slaughtered horse ovaries. These oocytes formed the base of the experimental procedure.
• The oocytes were placed in a vitrification solution containing ethylene glycol, Ficoll, and sucrose. This solution was intended to facilitate the vitrification process, which aims to cryopreserve the oocytes. The process involved transitioning the oocytes into a glass-like state without the formation of ice crystals.
• Before introducing the oocytes into the solution, some were pre-exposed to a 20% ethylene glycol solution for either 10 or 20 minutes, while others were directly transferred.
• The procedure was conducted at two different temperatures: 20 and 30 degrees centigrade, to evaluate the impact of temperature on the vitrification process.

Results and Observations

• After vitrification and warming, the viability of the oocytes was determined by observing their maturation in cell culture. Comparisons were made between groups denoting pre-exposure, temperatures, and maturation rates.
• The research found that a higher percentage of oocytes reached the metaphase II stage—the stage marking successful in vitro maturation—in groups that received pre-exposure to the ethylene glycol solution (Groups 2, 3, 5, and 6) versus those that did not (Groups 1 and 4).
• Untreated control oocytes had a 55.6% meiosis completion rate in vitro, offering a baseline for comparison.
• The researchers used Transmission Electron Microscopy to observe and compare the ultrastructure of vitrified oocytes with untreated and solely EFS-exposed oocytes.

Morphological Changes and Viability

• One observation from the study was that the vitrification process caused several ultrastructural alterations in the oocytes, such as mitochondrial swelling, damage to communication between the oocyte and surrounding cumulus cells, and the presence of vacuoles (spaces or voids within the cell).
• However, these changes were not consistent across all samples.
• Exposure of oocytes to EFS solution alone also resulted in changes to the cell ultrastructure—although to a lesser extent. Notably, the EFS exposure induced vacuoles to the same extent as the vitrification process.
• The research suggested that the viability loss in some EFS-exposed or vitrified oocytes could be due to morphological changes such as the destruction of intercellular communications between cumulus cells and oocytes.
• Despite these changes, the results suggested that immature horse oocytes can be effectively cryopreserved via vitrification with EFS solution.