日本RIKEN生物系统动力学研究中心（BDR）Ichiro Hiratani，Tomoya S. Kitajima和Hirohisa Kyogoku共同合作，近期取得重要工作进展。他们研究发现了DNA复制时序程序出现时胚胎基因组的不稳定性。相关研究成果2024年8月28日在线发表于《自然》杂志上。

据介绍，忠实的DNA复制对基因组的完整性至关重要。复制不足的DNA会导致染色体分离缺陷，这在胚胎发育过程中很常见。然而，在早期哺乳动物胚胎中，对DNA复制的调控仍然知之甚少。

研究人员构建了一个着床前小鼠胚胎的单细胞全基因组DNA复制图谱，并发现了一个伴随着短暂基因组不稳定期的突然复制程序切换。在1细胞和2细胞胚胎中，研究人员观察到完全没有复制时序程序，整个基因组使用极其缓慢的复制叉逐渐均匀地复制。在4细胞胚胎中，体细胞样复制时间程序突然开始。

然而，分叉速度仍然很慢，S期延长，复制应激、DNA损伤和修复的标志物增加。随后，断裂型染色体分离错误增加，特别是在4到8细胞分裂期间，断裂点富集在晚期复制区域。这些错误被核苷补充所挽救，核苷补充加速了分叉速度并减轻了复制压力。到8细胞阶段，分叉速度加快，S期不再延长，染色体畸变减少。

因此，在小鼠的正常发育过程中存在一个短暂的基因组不稳定性时期，在此之前的S阶段缺乏复制体级调控和巨碱基级复制定时调控之间的协调，这意味着它们之间的协调与基因组稳定性之间存在联系。

附：英文原文

Title: Embryonic genome instability upon DNA replication timing program emergence

Author: Takahashi, Saori, Kyogoku, Hirohisa, Hayakawa, Takuya, Miura, Hisashi, Oji, Asami, Kondo, Yoshiko, Takebayashi, Shin-ichiro, Kitajima, Tomoya S., Hiratani, Ichiro

Issue&Volume: 2024-08-28

Abstract: Faithful DNA replication is essential for genome integrity1,2,3,4. Under-replicated DNA leads to defects in chromosome segregation, which are common during embryogenesis5,6,7,8. However, the regulation of DNA replication remains poorly understood in early mammalian embryos. Here we constructed a single-cell genome-wide DNA replication atlas of pre-implantation mouse embryos and identified an abrupt replication program switch accompanied by a transient period of genomic instability. In 1- and 2-cell embryos, we observed the complete absence of a replication timing program, and the entire genome replicated gradually and uniformly using extremely slow-moving replication forks. In 4-cell embryos, a somatic-cell-like replication timing program commenced abruptly. However, the fork speed was still slow, S phase was extended, and markers of replication stress, DNA damage and repair increased. This was followed by an increase in break-type chromosome segregation errors specifically during the 4-to-8-cell division with breakpoints enriched in late-replicating regions. These errors were rescued by nucleoside supplementation, which accelerated fork speed and reduced the replication stress. By the 8-cell stage, forks gained speed, S phase was no longer extended and chromosome aberrations decreased. Thus, a transient period of genomic instability exists during normal mouse development, preceded by an S phase lacking coordination between replisome-level regulation and megabase-scale replication timing regulation, implicating a link between their coordination and genome stability.

DOI: 10.1038/s41586-024-07841-y

Source: https://www.nature.com/articles/s41586-024-07841-y