Fanconi anemia (FA) is a rare chromosomal instability syndrome with various clinical features and high cancer incidence. Despite being a DNA repair disorder syndrome and a frequently observed clinical hypersensitivity of FA patients towards ionizing radiation, the experimental evidence regarding the efficiency of radiation-induced DNA double-strand break (DSB) repair in FA is very controversial. Here, we performed a thorough analysis of the repair of radiation-induced DSBs in G1 and G2 in FA fibroblasts of complementation groups A, C, D1 (BRCA2), D2, E, F, G and P (SLX4) in comparison to normal human lung and skin fibroblasts. γH2AX, 53BP1, or RPA foci quantification after X-irradiation was combined with cell cycle markers. Cytogenetic analyses were performed on first metaphases after irradiation in G1 and by premature chromosome condensation after exposure in G2. Furthermore, the role of canonical-NHEJ and alternative-NHEJ for the fidelity of the repair of radiation-induced DSBs was examined. In FA fibroblasts, DSB repair was normal in G1 but compromised and more error-prone in the slow repair component of G2 as suggested by higher yields of radiation-induced γH2AX and 53BP1 foci as well as chromatid exchanges. However, RPA foci quantification in G2 indicated proficiency for homology-directed repair of DSBs in FA except for FA D1 (BRCA2). In lung fibroblasts, DSB repair in G1 was conducted with normal kinetics but elevated chromosome exchanges compared to skin fibroblasts. The overall repair of radiation-induced DSBs and the formation of chromosome exchanges in normal and FA fibroblasts in G1 and G2 were governed by canonical-NHEJ with no contribution of alternative-NHEJ. Together, we show impaired repair of radiation-induced DSBs in various FA complementation groups in the slow repair component of G2 that might promote the formation of potentially oncogenic aberrations and clinical radiation hypersensitivity.

范可尼贫血（FA）是一种罕见的染色体不稳定综合征，具有各种临床特征和高癌症发生率。尽管是DNA修复障碍综合症，并且FA患者对电离辐射经常观察到的临床超敏性，但有关FA中由辐射引起的DNA双链断裂（DSB）修复效率的实验证据仍然存在争议。在这里，我们对与正常组相比，互补组A，C，D1（BRCA2），D2，E，F，G和P（SLX4）的FA成纤维细胞中G1和G2中辐射诱导的DSBs的修复进行了彻底的分析。人肺和皮肤成纤维细胞。X射线照射后的γH2AX，53BP1或RPA病灶定量与细胞周期标记物结合使用。细胞遗传学分析在G1中照射后的第一个中期进行，并在G2中暴露后通过过早的染色体凝结进行。此外，还研究了经典的-NHEJ和替代的-NHEJ在保真度方面的作用。在FA成纤维细胞中，DSB修复在G1中是正常的，但在G2的缓慢修复组分中受损且易出错，这是由辐射诱导的γH2AX和53BP1病灶的更高产量以及染色单体交换所暗示的。但是，G2中的RPA病灶定量表明，除了FA D1（BRCA2）外，FA中DSB的同源性直接修复能力也很强。在肺成纤维细胞中，G1中的DSB修复以正常动力学进行，但与皮肤成纤维细胞相比，染色体交换增加。辐射诱导的DSB的整体修复以及G1和G2中正常和FA成纤维细胞中染色体交换的形成均受规范-NHEJ的控制，而没有其他-NHEJ的贡献。在一起，我们显示G2的慢速修复组件中各个FA补体组中辐射诱导的DSB修复受损，这可能会促进潜在的致癌像差的形成和临床辐射超敏反应。