Pre- and postnatal development of mouse embryos after storage for different periods at cryogenic temperatures

Pregnant mares' serum gonadotropin source influences fertilization and fresh or thawed embryo development, but the effect is genotype specific

The influence of the source of pregnant mares' serum gonadotropin (PMSG) on the number, quality, and in vitro development of mouse embryos before and after freezing was evaluated among three genotypes: N:NIH(S), C57BL/6N, and C3H/HeN-MTV-Immature females were given PMSG from one of five commercial sources. Following collection (116 hr later), embryos were evaluated for stage of development, and four- to eight-cell embryos were pooled within genotype and assigned to standardized fresh or freeze-thaw culture trials. Different PMSG sources stimulated the production of different numbers of total embryos (P less than 0.05) but not necessarily more embryos suitable for freezing. Differences in embryo production among genotypes indicated that absolute embryo numbers using a single mouse genotype may not accurately reflect the potency of a specific gonadotropin source. The PMSG source also affected the ability of an embryo to survive in culture either immediately after collection or after frozen storage. The effect, however, was genotype specific, with some mouse strains being relatively insensitive to PMSG source, whereas gonadotropin source played a major role in determining in vitro viability in others. Development rates for freshly collected embryos differed, often inconsistently, from those of thawed embryos regardless of the PMSG source used, demonstrating that fresh embryo development cannot be used to estimate expected post-thaw survival. In vitro development of thawed embryos is influenced not only by genotype, but also the source of the gonadotropin used to promote follicular development and oocyte maturation. These findings may explain, in part, the wide variation in embryo viability and culture rates reported among laboratories and intraspecies animal populations.

Effect of rapid addition and dilution of dimethyl sulfoxide on the viability of frozen-thawed rabbit morulae

The aim of the present study was to examine effects of altering thawing conditions and procedure of addition and dilution of Me2SO on the viability of frozen-thawed rabbit morulae. Five hundred and sixty two rabbit morulae were cooled from room temperature to -80 degrees C at 1 degree C/min in the presence of 1.5 M dimethyl sulfoxide (Me2SO) using a programmable liquid nitrogen vapor freezing machine with an automatic seeding device, cooled rapidly, and stored in liquid nitrogen. When Me2SO was added in a single step, the frozen embryos were thawed in ambient air at 40 degrees C/min and Me2SO was diluted in a single step, 99 of 107 (93%) embryos cultured for 48 hr and 12 of 32 (38%) embryos transferred to 6 recipients developed to expanding blastocysts and viable fetuses, respectively. When Me2SO was added in a single step and the frozen embryos were thawed at the same rate and transferred directly without removal of Me2SO to culture media or oviducts of 8 recipients, 67 of 75 (89%) embryos cultured and 12 of 40 (30%) embryos transferred developed to expanding blastocysts and viable fetuses, respectively. There were no significant differences between these survival rates and survival rates obtained by conventional method, i.e., frozen embryos were thawed at 4 degrees C/min by interrupted slow method and Me2SO was added and diluted in a stepwise manner.

Effects of low temperatures on survival of frozen-thawed mouse embryos

Almost no damage to mouse morulae was observed between 0 and -40 degrees C, and freezing damage to embryos in DMSO, glycerol or ethylene glycol occurred after exposure to -60, -50 or -50 degrees C, respectively. Cooling embryos in DMSO or glycerol to temperatures below -50 to -60 degrees C increased freezing damage. To the contrary, in the presence of ethylene glycol, no more damage occurred after exposure to temperatures below -50 degrees C.