The establishment of pregnancy is a well-regulated process that involves the development of a viable blastocyst, conceptus elongation, maternal recognition of pregnancy, implantation, and the onset of placentation. Pregnancy loss is a major factor limiting reproductive efficiency in livestock species. In cattle, most embryonic losses occur during the first month of gestation. The genetic and epigenetic regulation of embryonic and placental development in ruminants is still poorly understood. To investigate the transcriptome profile of the bovine conceptus during elongation, Angus heifers (n = 8) were superovulated and bred using semen from a proven high-fertility Bos indicus sire. Heifers were flushed on d 14 of gestation using a standard nonsurgical flushing technique. Recovered conceptuses were individually photographed and snap-frozen for total RNA extraction and bulk mRNA sequencing. Recovered conceptuses were classified based on size into ovoid (0.2 – 5mm; n = 6), tubular (<15 mm; n = 7), or filamentous (>16 mm; n = 7). Differentially expressed genes (DEG: FDR < 0.05) were determined using DESeq2 analysis and were functionally annotated using DAVID. The most pronounced transcriptomic changes were identified between the ovoid and tubular stages, with 5,937 DEGs (2,913 upregulated and 3,024 downregulated) and affected pathways were primarily involved in ribosome assembly and rRNA processing. There were 3,966 DEGs (2,069 upregulated and 1,897 downregulated) between the ovoid and filamentous stages, and the most significant pathways were involved in protein translation, embryonic development, and cell cycle. The transition between tubular to filamentous presented 1,435 DEGs (775 upregulated and 660 downregulated) and significant pathways were involved in protein degradation, cell division, cell cycle, protein stabilization, and mRNA splicing. Our findings indicate that the greatest alterations in the transcriptome occur precisely at the initiation of elongation, suggesting that the bovine conceptus undergoes major structural changes at the outset of this process. This major shift in gene expression is presumed to be necessary to support the subsequent exponential growth phase of elongation, required for maternal recognition of pregnancy.

中文翻译：

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121 揭开牛孕体伸长的生物学原理

妊娠的建立是一个受到良好调控的过程，涉及可行囊胚的发育、概念伸长、母体对妊娠的识别、着床和胎盘的开始。妊娠损失是限制牲畜繁殖效率的主要因素。在牛中，大多数胚胎损失发生在妊娠第一个月。反刍动物胚胎和胎盘发育的遗传和表观遗传调控仍知之甚少。为了研究伸长过程中牛概念的转录组谱，安格斯小母牛 (n = 8) 被超排卵并使用来自经过验证的高生育力 Bos indicus 公牛的精液进行繁殖。使用标准非手术冲洗技术在妊娠第 14 天对小母牛进行冲洗。回收的受孕体被单独拍照并快速冷冻，以进行总 RNA 提取和批量 mRNA 测序。回收的受孕体根据大小分为卵形（0.2 – 5mm；n = 6）、管状（<15 mm；n = 7）或丝状（>16 mm；n = 7）。使用DESeq2分析确定差异表达基因(DEG：FDR＜0.05)并使用DAVID进行功能注释。最明显的转录组变化在卵球形和管状阶段之间被发现，有 5,937 个 DEG（2,913 个上调和 3,024 个下调），受影响的途径主要涉及核糖体组装和 rRNA 加工。卵圆形阶段和丝状阶段之间存在 3,966 个 DEG（2,069 个上调和 1,897 个下调），最重要的途径涉及蛋白质翻译、胚胎发育和细胞周期。管状到丝状之间的转变存在 1,435 个 DEG（775 个上调和 660 个下调），并且重要的途径涉及蛋白质降解、细胞分裂、细胞周期、蛋白质稳定和 mRNA 剪接。我们的研究结果表明，转录组的最大变化恰好发生在伸长开始时，这表明牛概念在此过程开始时经历了重大的结构变化。据推测，基因表达的这种重大转变对于支持随后的指数生长期伸长是必要的，这是母体识别怀孕所必需的。