Survival of mouse embryos after vitrification depending on the cooling rate of the cryoprotectant solution

Growth differentiation factor 9 and cumulus cell supplementation in in vitro maturation culture media enhances the viability of human blastocysts

Objective

In vitro maturation (IVM) of immature oocytes can be useful for some infertile patients. In IVM programs, the rates of embryo formation and pregnancy are low. Therefore, it is essential to recognize the main factors involved in regulating oocyte maturation in vitro. The purpose of this study was to investigate the effects of growth differentiation factor 9 (GDF9) and cumulus cell (CC) supplementation in IVM medium on the rates of embryo formation and viability of human blastocysts.

Methods

A total of 80 germinal vesicle oocytes from stimulated cycles underwent an IVM program. The oocytes were divided into four groups, where group I consisted of IVM media only and served as the control, group II consisted of IVM+CCs, group III consisted of IVM+GDF9 (200 ng/mL), and group IV consisted of IVM+CCs+GDF9 (200 ng/mL). Intracytoplasmic sperm injection was performed on the IVM oocytes, and the cleavage embryos that were generated were vitrified. Following thawing, the embryos were cultured for 3 additional days, and the viability rates of the developed blastocysts were determined.

Results

The maturation rate of the oocytes did not differ significantly across the four groups. The fertilization rate in group II was significantly higher than that in the control group (76.5% vs. 46.2%). Embryo formation was significantly more frequent in all experimental groups than in the control group, while blastocyst formation did not show significant differences in the three experimental groups compared to the control. The mean viability rates in groups II, III, and IV were 58.16%, 55.91%, and 55.95%, respectively, versus 37.78% in the control group (p<0.05).

Conclusion

Supplementation of IVM culture media with GDF9 and CCs enhanced the fertilization, embryo formation, and viability rates of blastocysts generated from vitrified cleavage embryos.

Mouse embryo cryopreservation utilizing a novel high-capacity vitrification spatula

Embryo cryopreservation is an indispensable technique in reproductive programs and in animal facilities where genetically modified mice are used extensively. Here we report the use of a vitrification spatula (VS) that can be readily homemade and has a large holding capacity to vitrify preimplantation mammalian embryos in a micro-drop employing ultra-rapid cooling in liquid nitrogen (LN2). Vitrified one-cell embryos and morulae have high survival rates after thawing, and the fertility of the derived progeny is comparable to that of the control unvitrified group. The large holding capacity (up to 50 embryos per VS) does not only allow rapid expansion of storage capacity for additional mouse strains but also opens up the possibility to streamline transgenic mice generation procedures in transgenic facilities.

Effect of vitrification technique and assisted hatching on rabbit embryo developmental rate

The aim of the study was to determine the efficiency of two vitrification techniques followed by two assisted hatching (AH) techniques based on post-thaw developmental capacity of precompacted rabbit embryos and their ability to leave the zona pellucida (hatching) during in vitro culture. The total cell number and embryo diameter as additional markers of embryo quality after warming were evaluated. In vivo fertilized, in vitro cultured 8–12-cell rabbit embryos obtained from superovulated rabbit does were cryopreserved by two-step vitrification method using ethylene glycol (EG) as cryoprotectant or by one-step vitrification method with EG and Ficoll (EG+Ficoll). Thawed embryos were subjected to enzymatic or mechanical AH. Vitrified EG group showed significantly lower (P < 0.05) blastocyst rate (22.5%) and hatching rate (15%) than those vitrified with EG + Ficoll (63 and 63% resp.) and that of control (97 and 97% respectively). Significantly lower values of total cell number (P < 0.05) as well as embryo diameter (P < 0.01) in EG group compared with EG + Ficoll and control group were recorded. No significant difference was found in developmental potential of warmed embryos treated by either mechanical or enzymatic AH. The present study demonstrates that the EG + Ficoll vitrification protocol provides superior embryo survival rates over the EG vitrification protocol for 8–12-cell stage precompacted rabbit embryos. No positive effect of either mechanical or enzymatic AH on the post-thaw viability and quality of rabbit embryos in vitro was observed.