Surrallés J, Natarajan A T
Department of Radiation Genetics and Chemical Mutagenesis, Leiden University, Leiden, Netherlands.
Mutat Res. 1998 May 11;414(1-3):117-24. doi: 10.1016/s1383-5718(98)00046-1.
The inactive X-chromosome provides a unique opportunity to study the role of transcriptional activity and chromatin condensation in the repair of chromosome damage. We induced chromosome breakage in human lymphocytes with X-rays (1 or 2 Gy) in either G0 and G1 phase of the cell cycle, and in the presence or absence of an inhibitor of double strand break repair, adenine 9-beta-D-arabinofuranoside (Ara-A). Chromosomal aberrations involving the X-chromosome were detected by means of fluorescence in situ hybridization with an X-chromosome specific red painting probe. The activation status of the X-chromosomes involved in the chromosomal aberrations was determined by simultaneous immunocytogenetics with FITC-conjugated antibodies against BrdUrd incorporated at late S-phase to distinguish the late replicating inactive X-chromosome in green-yellow. This multicolor approach allowed us to study and compare breakage and the extent of repair in the active and inactive X-chromosome. Our data indicate that both chromosomes responded with a similar radiosensitivity. This observation was consistent at both X-ray doses and at the two stages of the cell cycle analyzed. However, the number of chromosomal aberrations involving the inactive X-chromosome was increased after repair inhibition with Ara-A. The differential sensitivity to repair inhibition was observed in G0 after 1 Gy and in G1 after 2 Gy. Thus, the activation status of the X-chromosome might be a source of heterogeneity in breakage and repair. These observations suggest that there is heterogeneous repair when the active and the inactive X-chromosomes are compared and that the observed fragility is the result of a compromise between the actual number of breaks induced in each chromosome and their differential processing.
失活的X染色体为研究转录活性和染色质凝聚在染色体损伤修复中的作用提供了独特的机会。我们用X射线（1或2 Gy）在细胞周期的G0和G1期，以及在存在或不存在双链断裂修复抑制剂腺嘌呤9-β-D-阿拉伯呋喃糖苷（Ara-A）的情况下，诱导人淋巴细胞中的染色体断裂。通过用X染色体特异性红色涂染探针进行荧光原位杂交来检测涉及X染色体的染色体畸变。通过与针对在S期晚期掺入的BrdUrd的FITC偶联抗体进行同步免疫细胞遗传学，以区分绿色黄色的晚期复制失活X染色体，来确定参与染色体畸变的X染色体的激活状态。这种多色方法使我们能够研究和比较活性和失活X染色体中的断裂和修复程度。我们的数据表明，两条染色体的放射敏感性相似。这一观察结果在两个X射线剂量以及所分析的细胞周期的两个阶段都是一致的。然而，在用Ara-A抑制修复后，涉及失活X染色体的染色体畸变数量增加。在1 Gy后的G0期和2 Gy后的G1期观察到对修复抑制的差异敏感性。因此，X染色体的激活状态可能是断裂和修复中异质性的一个来源。这些观察结果表明，当比较活性和失活X染色体时存在异质性修复，并且观察到的脆性是每条染色体中诱导的实际断裂数量与其差异处理之间折衷的结果。
