Effects of various cryopreservations on chromosomes of oocytes of experimental and domestic animals

通过将保存在液氮中的胚胎成功地移植到发情同步的受体体内，可以在几种哺乳动物中获得新生儿。胚胎和卵母细胞的冷冻保存系统是哺乳动物遗传资源中利用配子最重要的技术之一。然而，冷冻保存的卵母细胞的成功率和受精率一直低于分离的胚胎。冷冻解冻的小鼠卵母细胞体外受精后获得的第一卵裂胚胎多倍体增加，多倍体来源于卵母细胞的二倍体。然而，也有报道称，冷冻解冻后卵母细胞的孤雌激活发生率并没有增加。由于对冷冻解冻卵母细胞需要更详细的细胞遗传学信息，我们对第一次卵裂小鼠的染色体和来自冷冻解冻卵母细胞的牛卵进行了分析。说明冷冻保护剂的毒性和冷冻对卵母细胞染色体的物理损伤是导致染色体结构异常的主要原因。然而，在牛卵中，染色体结构异常的发生率并不显著。

Newborns in several mammals can be obtained by successful transfer of embryos stored in liquid nitrogen into recipients synchronized estrously. The cryopreservation system for embryos and oocytes is one of the most important techniques for gamete use in mammalian genetic resources. However, the successful survival rate and fertilization rate of cryopreserved oocytes have been lower than those of the embryos divided. An increase in polyploidy was found in first-cleavage mouse embryos obtained from frozen-thawed oocytes fertilized in vitro, and the polyploids were derived from digyny in the oocytes. However, it was also reported that the incidence of parthenogenetic activation in frozen-thawed oocytes was not increased. Because more detailed cytogenetical information about frozen-thawed oocytes has been required, we analyzed chromosomes of 1st-cleavage mouse and bovine eggs derived from frozen-thawed oocytes.The present study showed that high incidence of chromosomes having structural aberrations was observed in the 1st-cleavage mouse eggs obtained from frozen-thawed oocytes fertilized in vitro. It appears that the causes of structural aberrations of chromosomes are cryoprotectant toxicity and the physical damage of cryopreservation to the chromosomes of oocytes. In bovine eggs, however, the incidence of chromosomes having structural aberrations was not significant.