Cryopreservation of mammalian oocytes

Effect of supplementation of vitrification solution on post-thaw survivability rate of porcine follicular oocytes

Oocytes (510) with two or more cumulus cell layers adhered to zona pellucida obtained by aspiration from follicles (2–8 mm dia) of 127 abattoir porcine ovaries were utilized to study the effect of supplementation of 0.5 M sucrose (Suc), 50 mg/ml polyvinyl pyrrolidone (PVP) and Suc + PVP into two different vitrification solutions, i.e. 35% concentration of both ethylene glycol (EG)+ propylene glycol (PG) and EG + dimethyl sulphoxide (DMSO). Vitrified post-thaw oocytes with intact zona pellucida and vitelline membrane, normal spherical shape and dark and evenly granulated cytoplasm under a stereo-zoom microscope were considered as viable. Out of the three supplements treatments, supplementation with sucrose + PVP combination and sucrose alone resulted in significantly higher mean post-thaw survivability rate of vitrified oocytes both for EG + PG and EG + DMSO as compared to the supplementation with PVP alone. It was concluded that addition of sucrose alone or in combination with PVP in vitrification solution, significantly improved survivability of vitrified porcine follicular oocytes.

Effect of type and concentration of cryoprotectant on post-thaw survivability of vitrified porcine follicular oocytes

A total of 950 and 510 oocytes with two or more cumulus cell layers adhered to zona pellucida obtained by aspiration from follicles (2–8 mm dia) of 315 and 135 abattoir porcine ovaries, respectively, were utilized in the study to find the effect of cryoprotectant and concentration on post-thaw survivability of porcine follicular oocytes. Vitrified post-thaw oocytes with intact zona pellucida and vitelline membrane, normal spherical shape and dark and evenly granulated cytoplasm under a stereo-zoom microscope were considered as viable. Out of the 10 cryoprotectant treatments i.e. ethylene glycol (EG), propylene glycol (PG), dimethyl sulphoxide (DMSO), glycerol (GL), EG + PG, EG + DMSO, EG + GL, PG + DMSO, PG + GL and DMSO + GL used for vitrification of oocytes at a concentration of 35%, the post-thaw survivability rate was the highest in EG +DMSO followed by EG + PG group which had significantly higher mean post-thaw survived oocytes as compared to GL, PG + DMSO, PG + GL and DMSO + GL groups. Exposing the oocytes to 30, 35 and 40% of EG + DMSO and EG + PG yielded no significant difference in post-thaw survivability rate of vitrified oocytes, although the highest value was obtained with 35%. It was concluded that 35 to 40% EG + DMSO yielded efficient vitrification of porcine oocytes.

Effect of cryopreservation on acetylation patterns of lysine 12 of histone H4 (acH4K12) in mouse oocytes and zygotes

PURPOSE

to determine the effect of cryopreservation on acH4K12 in oocytes and their respective zygotes.

METHODS

AcH4K12 in fresh or vitrified-warmed oocytes and their respective zygotes at 70 min-12 h post-fertilization were assessed using fluorescent staining.

RESULTS

1. AcH4K12 levels increased significantly in vitrified oocytes compared to controls. 2. Respective zygotes derived from vitrified oocytes had abnormal chromatin distribution or acH4K12 patterns before and after pronuclear formation.

CONCLUSION

Cryopreservation alters AcH4K12 patterns in oocytes, which subsequently affect the chromatin distribution and acH4K12 in fertilized oocytes.

The individual-cell-based cryo-chip for the cryopreservation, manipulation and observation of spatially identifiable cells. I: methodology

BACKGROUND

Cryopreservation is the only widely applicable method of storing vital cells for nearly unlimited periods of time. Successful cryopreservation is essential for reproductive medicine, stem cell research, cord blood storage and related biomedical areas. The methods currently used to retrieve a specific cell or a group of individual cells with specific biological properties after cryopreservation are quite complicated and inefficient.

RESULTS

The present study suggests a new approach in cryopreservation, utilizing the Individual Cell-based Cryo-Chip (i3C). The i3C is made of materials having appropriate durability for cryopreservation conditions. The core of this approach is an array of picowells, each picowell designed to maintain an individual cell during the severe conditions of the freezing--thawing cycle and accompanying treatments. More than 97% of cells were found to retain their position in the picowells throughout the entire freezing--thawing cycle and medium exchange. Thus the comparison between pre-freezing and post-thawing data can be achieved at an individual cell resolution. The intactness of cells undergoing slow freezing and thawing, while residing in the i3C, was found to be similar to that obtained with micro-vials. However, in a fast freezing protocol, the i3C was found to be far superior.

CONCLUSIONS

The results of the present study offer new opportunities for cryopreservation. Using the present methodology, the cryopreservation of individual identifiable cells, and their observation and retrieval, at an individual cell resolution become possible for the first time. This approach facilitates the correlation between cell characteristics before and after the freezing--thawing cycle. Thus, it is expected to significantly enhance current cryopreservation procedures for successful regenerative and reproductive medicine.