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

几种哺乳动物的新生儿可以通过将液氮中储存的胚胎成功地移植到发情同步的受体中来获得。胚胎和卵母细胞的冷冻保存是哺乳动物配子利用的重要技术之一。然而，冻存卵母细胞的成功存活率和受精率一直低于分裂胚胎。小鼠卵母细胞冻融后体外受精获得的第一卵裂胚胎中多倍体增多，多倍体来源于卵母细胞中的双雌生殖。然而，也有报道称，冻融卵母细胞中孤雌激活的发生率并未增加。由于需要更详细的冻融卵母细胞的细胞遗传学信息，我们对小鼠和牛冻融卵母细胞体外受精后第一次卵裂卵的染色体进行了分析，发现小鼠冻融卵母细胞体外受精后第一次卵裂卵染色体结构畸变的发生率较高。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造成染色体结构畸变的原因。然而，在牛卵子中，染色体结构畸变的发生率并不显着。

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.