Inefficient Double-Strand Break Repair in Murine Rod Photoreceptors with Inverted Heterochromatin Organization
Inefficient Double-Strand Break Repair in Murine Rod Photoreceptors with Inverted Heterochromatin Organization
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DOI：
10.1016/j.cub.2014.03.061
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发表时间：
2014-05-19
期刊：
影响因子：
9.2
通讯作者：
Loebrich, Markus
中科院分区：
文献类型：
--
作者：
Frohns, Antonia;Frohns, Florian;Loebrich, Markus
背景：DNA双链断裂（DSB）修复对于维持基因组稳定性至关重要，而染色质组织是影响修复效率的重要因素之一。小鼠棒状光感受器具有倒置的异染色质结构，在细胞核中间含有一个大的色心，为研究活体动物异染色质中的DSB修复提供了一个独特的模型系统。结果：我们观察到，在损伤诱导后1天内，成体视杆光感受器仅修复了一半的诱导dsb，这一缺陷在任何其他类型的成体视网膜细胞和出生后第4天小鼠的视杆光感受器前体细胞中均未观察到。我们发现，成年野生型杆状细胞缺乏涉及ATM的修复途径，ATM是一种通过磷酸化KAP1和促进异染色质松弛来促进异色DSB修复的蛋白质。值得注意的是，我们观察到杆状细胞在dsb处不能稳定地积累活跃的ATM，表现出低KAP1水平，并表现出高水平的SPOC1（一种抑制KAP1磷酸化的因子）。总的来说，这导致KAP1磷酸化显著降低，无法修复异色dsb。结论：由于杆状细胞具有独特的异色结构，能够在低光子水平下聚焦传输光，因此在dsb存在的情况下，KAP1无法磷酸化和异色质无法松弛可能有助于维持这种结构和杆状细胞的功能。总的来说，我们的研究结果表明，成体杆状细胞独特的染色质组织使它们无法有效地修复异时性DSB，这为异染色质影响哺乳动物体内DSB修复提供了证据。
Background: DNA double-strand break (DSB) repair is crucial for the maintenance of genomic stability, and chromatin organization represents one important factor influencing repair efficiency. Mouse rod photoreceptors with their inverted heterochromatin organization containing a single large chromocenter in the middle of the nucleus provide a unique model system to study DSB repair in heterochromatin of living animals.Results: We observed that adult rod photoreceptors repair only half of the induced DSBs within 1 day after damage induction, a defect that is neither observed in any other cell type of the adult retina nor in rod photoreceptor precursor cells of postnatal day 4 mice. We show that adult wild-type rods are deficient in a repair pathway involving ATM, a protein that promotes heterochromatic DSB repair by phosphorylating KAP1 and facilitating heterochromatin relaxation. Of note, we observed that rods fail to robustly accumulate active ATM at DSBs, exhibit low KAP1 levels, and display high levels of SPOC1, a factor suppressing KAP1 phosphorylation. Collectively, this results in dramatically reduced KAP1 phosphorylation and the inability to repair heterochromatic DSBs.Conclusions: Because the distinct heterochromatic structure of rods focuses transmitting light to enable vision at low photon levels, the inability to phosphorylate KAP1 and the failure to relax heterochromatin could serve to maintain this structure and the functionality of rods in the presence of DSBs. Collectively, our findings show that the unique chromatin organization of adult rods renders them incapable to efficiently repair heterochronnatic DSBs, providing evidence that heterochromatin affects mammalian DSB repair in vivo.