DNA polymerase zeta contributes to heterochromatin replication to prevent genome instability

The DNA polymerase zeta (Polζ) plays a critical role in bypassing DNA damage. REV3L, the catalytic subunit of Polζ is also essential in mouse embryonic development and cell proliferation for reasons that remain incompletely understood. In this study, we reveal that REV3L protein interacts with heterochromatin components including repressive histone marks, and localizes in pericentromeric regions through direct interaction with HP1 dimer. We demonstrate that Polζ/REV3L ensures progression of replication forks through difficult-to-replicate pericentromeric heterochromatin, thereby preventing spontaneous chromosome break formation. We also find that Rev3l-deficient cells are compromised in the repair of heterochromatin-associated double-strand breaks, eliciting deletions in late replicating regions. Lack of REV3L leads to further consequences that may be ascribed to heterochromatin replication and repair-associated functions of Polζ, with a disruption of the temporal replication program at specific loci. This is correlated with changes in epigenetic landscape and transcriptional control of developmentally regulated genes. These results reveal a new function of Polζ in preventing chromosome instability during replication of heterochromatic regions.

DNA聚合酶ζ（DNA polymerase zeta，Polζ）在绕过DNA损伤的过程中发挥关键作用。作为Polζ的催化亚基，REV3L在小鼠胚胎发育与细胞增殖中同样不可或缺，但其具体调控机制仍未完全明晰。本研究揭示，REV3L蛋白可与包括抑制性组蛋白修饰在内的异染色质组分相互作用，并通过直接结合异染色质蛋白1（HP1）二聚体定位于着丝粒周边区域。我们证实，Polζ/REV3L可保障复制叉在难以复制的着丝粒周边异染色质区域顺利推进，进而防止自发性染色体断裂的形成。此外，我们还发现Rev3l缺陷细胞在修复异染色质相关双链断裂时存在功能缺陷，最终引发复制晚期区域的缺失突变。REV3L的缺失还会引发更多后续效应，这些效应可归因于Polζ在异染色质复制与修复过程中的功能，同时会破坏特定基因组位点的时序复制程序。这一现象与发育调控基因的表观遗传景观及转录调控的改变密切相关。上述研究结果揭示了Polζ在异染色质区域复制过程中维持染色体稳定性的全新功能。