Department of Pharmacology, Institute of Bioscience, University of São Paulo State (UNESP), Botucatu, São Paulo, Brazil.
Theriogenology. 2013 Jan 15;79(2):351-7. doi: 10.1016/j.theriogenology.2012.10.003. Epub 2012 Nov 12.
Heat stress is an important cause of poor development and low survival rates in bovine embryos. Experiments were conducted to test the hypothesis that Bos indicus embryos are more resistant to heat stress than are Bos taurus embryos. In experiment 1, Nelore and Jersey embryos from oocyte pick-up-derived oocytes were submitted to heat stress (96 hours post-insemination, 41 °C, 6 hours), developmental ratios were assessed at Day 7 (Day 0 = day of fertilization), and blastocysts were frozen for RNA extraction. Experiment 2 evaluated expression of COX2, CDX2, HSF1, and PLAC8 in previously frozen blastocysts. In experiment 3, Nellore and Angus embryos from oocyte pick-up-derived oocytes were submitted to heat stress (96 hours post-insemination, 41 °C, 12 hours) and transferred to recipients on Day 7. In experiment 4, embryos developed as in experiment 3 were fixed for Terminal deoxynucleotidyl transferase dUTP nick end labeling labeling and total cell counting. In experiment 1, heat stress decreased the percentage of Jersey oocytes that became blastocysts, but had no effect on Nellore embryos (34.6%, 25.0%, 39.5%, and 33.0% for Jersey control, Jersey heat-stressed, Nellore control, and Nellore heat-stressed oocytes, respectively; P < 0.05). In experiment 2, heat stress decreased (P < 0.05) expression of CDX2 and PLAC8, with higher expression of these genes in Nellore embryos than in Jersey embryos. Heat stress also decreased (P < 0.05) expression of COX2 in Jersey embryos, but had no effect on Nellore embryos. Expression of HSF1 was decreased (P < 0.05) by heat stress in both breeds, with a greater effect in Nellore embryos. In experiment 3, heat stress tended (P = 0.1) to decrease the percentage of pregnancies among cows (Day 30 to 35) that received Angus embryos. In experiment 4, heat stress increased (P < 0.05) the percentage of apoptotic blastomeres, but had no breed-specific effects. In addition, Nellore embryos had fewer (P < 0.05) Terminal deoxynucleotidyl transferase dUTP nick end labeling- positive blastomeres than did Angus embryos. We concluded that the detrimental effects of heat stress were dependent upon embryo breed and were more evident in Bos taurus embryos than in Bos indicus embryos.
热应激是牛胚胎发育不良和存活率低的一个重要原因。进行了实验以验证假设，即印度野牛胚胎比瘤牛胚胎更能抵抗热应激。在实验 1 中，从卵母细胞采集获得的卵母细胞中取出Nelore 和 Jersey 胚胎，并进行热应激处理（受精后 96 小时，41°C，6 小时），在第 7 天（受精日为 0 天）评估胚胎发育率，并将囊胚冷冻用于 RNA 提取。实验 2 评估了先前冷冻的囊胚中 COX2、CDX2、HSF1 和 PLAC8 的表达。在实验 3 中，从卵母细胞采集获得的卵母细胞中取出 Nellore 和 Angus 胚胎，并进行热应激处理（受精后 96 小时，41°C，12 小时），然后在第 7 天移植到受体中。在实验 4 中，将胚胎按实验 3 进行固定，用于末端脱氧核苷酸转移酶 dUTP 缺口末端标记和总细胞计数。在实验 1 中，热应激降低了 Jersey 卵母细胞发育为囊胚的百分比，但对 Nellore 胚胎没有影响（Jersey 对照组、Jersey 热应激组、Nellore 对照组和 Nellore 热应激组的囊胚百分比分别为 34.6%、25.0%、39.5%和 33.0%；P<0.05）。在实验 2 中，热应激降低了（P<0.05）CDX2 和 PLAC8 的表达，Nellore 胚胎中这些基因的表达高于 Jersey 胚胎。热应激还降低了 Jersey 胚胎中 COX2 的表达，但对 Nellore 胚胎没有影响。HSF1 的表达在两种品种中均受到热应激的降低（P<0.05），Nellore 胚胎的影响更大。在实验 3 中，热应激导致（P=0.1）接受 Angus 胚胎的母牛（第 30 至 35 天）怀孕百分比降低。在实验 4 中，热应激增加了（P<0.05）凋亡的胚胎细胞百分比，但没有品种特异性影响。此外，与 Angus 胚胎相比，Nellore 胚胎的末端脱氧核苷酸转移酶 dUTP 缺口末端标记阳性胚胎细胞百分比更少（P<0.05）。我们得出结论，热应激的有害影响取决于胚胎品种，并且在瘤牛胚胎中比在印度野牛胚胎中更为明显。
