Vitrification Damage
The spindle distributing chromosomes in human egg cells can lose shape when thawed after rapid freezing. On August 22, a preprint was released about experiments with 234 human egg cells that matured in a lab from immature cells. The authors tracked at which stage of rapid freezing and thawing the structure distributing chromosomes changes. Vitrification is rapid freezing that turns water in the cell into a glass-like state.
Before cooling, the egg cell is placed in solutions with cryoprotectors - substances that partially replace water inside the cell. When thawing, the cryoprotectors are gradually removed, and water re-enters the cell. The authors monitored the same cells in a polarization microscope: the ordered protein threads of the spindle give a light signal there. When loading cryoprotectors, the signal was preserved; when thawing, it disappeared as the solutions were diluted.
Staining of the cells confirmed: the protein threads were preserved, but lost their stable spindle shape with two poles. Researchers checked if such a failure could be caused by the influx of water alone. In fresh lab-matured egg cells, they halved the osmolality of the medium - the concentration of dissolved substances. Water quickly entered the cells. Within eight minutes, the width of the spindle poles grew to approximately 160-180% of the original at n = 5; in the first minutes, the chromosomes remained aligned.
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PubMed Central (PMC)
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