In this study, the complexity of chromatin integrity was investigated in frozen‐thawed semen samples from 37 sires with contrasting fertility, expressed as 56‐day non‐return rates (NR56). Protamine deficiency, thiols, and disulfide bonds were assessed and compared with previously published data for DNA fragmentation index (DFI) and high DNA stainability (HDS). In addition, in vitro embryo development and sperm DNA methylation were assessed using semen samples from 16 of these bulls. The percentages of DFI and HDS were negatively associated with NR56 and cleavage rate and positively associated with sperm protamine deficiency (p < 0.05). Significant differences in cleavage and blastocyst rates were observed between bulls of high and low NR56. However, once fertilization occurred, further development into blastocysts was not associated with NR56. The differential methylation analysis showed that spermatozoa from bulls of low NR56 were hypermethylated compared to bulls of high NR56. Pathway analysis showed that genes annotated to differentially methylated cytosines could participate in different biological pathways and have important biological roles related to bull fertility. In conclusion, sperm cells from Norwegian Red bulls of inferior fertility have less compact chromatin structure, higher levels of DNA damage, and are hypermethylated compared with bulls of superior fertility.

中文翻译：

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对比生育力的挪威红牛的精子染色质完整性和 DNA 甲基化

在这项研究中，研究了来自 37 只生育力不同的公牛的冻融精液样本中染色质完整性的复杂性，表示为 56 天不返还率 (NR56)。对鱼精蛋白缺乏、硫醇和二硫键进行了评估，并与先前公布的 DNA 片段化指数 (DFI) 和高 DNA 染色性 (HDS) 数据进行了比较。此外，使用来自这些公牛中的 16 头的精液样本评估了体外胚胎发育和精子 DNA 甲基化。DFI和HDS的百分比与NR56和卵裂率呈负相关，与精子鱼精蛋白缺乏呈正相关（p < 0.05)。在高NR56和低NR56的公牛之间观察到卵裂和囊胚率的显着差异。然而，一旦受精发生，进一步发育成囊胚与 NR56 无关。差异甲基化分析表明，与高 NR56 的公牛相比，来自低 NR56 公牛的精子高度甲基化。通路分析表明，注释为差异甲基化胞嘧啶的基因可以参与不同的生物学通路，并具有与公牛生育能力相关的重要生物学作用。总之，与生育力高的公牛相比，生育力差的挪威红牛的精子细胞染色质结构不那么紧密，DNA损伤程度更高，并且甲基化程度高。