Falk Martin, Lukasova Emilie, Gabrielova Barbora, Ondrej Vladan, Kozubek Stanislav
Institute of Biophysics, Academy of Sciences of the Czech Republic, Kralovopolska 135, 612 65 Brno, Czech Republic.
Biochim Biophys Acta. 2007 Oct;1773(10):1534-45. doi: 10.1016/j.bbamcr.2007.07.002. Epub 2007 Jul 18.
We show that double strand breaks (DSBs) induced in chromatin of low as well as high density by exposure of human cells to gamma-rays are repaired in low-density chromatin. Extensive chromatin decondensation manifested in the vicinity of DSBs by decreased intensity of chromatin labelling, increased H4K5 acetylation, and decreased H3K9 dimethylation was observed already 15 min after irradiation. Only slight movement of sporadic DSB loci for short distances was noticed in living cells associated with chromatin decondensation around DSBs. This frequently resulted in their protrusion into the low-density chromatin domains. In these regions, the clustering (contact or fusion) of DSB foci was seen in vivo, and in situ after cell fixation. The majority of these clustered foci were repaired within 240 min, but some of them persisted in the nucleus for several days after irradiation, indicating damage that is not easily repaired. We propose that the repair of DSB in clustered foci might lead to misjoining of ends and, consequently, to exchange aberrations. On the other hand, the foci that persist for several days without being repaired could lead instead to cell death.
我们发现，人类细胞暴露于伽马射线后，在低密度和高密度染色质中诱导产生的双链断裂（DSB）在低密度染色质中得到修复。照射后15分钟即可观察到，DSB附近出现广泛的染色质解聚，表现为染色质标记强度降低、H4K5乙酰化增加以及H3K9二甲基化减少。在活细胞中，仅观察到零星的DSB位点有短距离的轻微移动，这与DSB周围的染色质解聚有关。这常常导致它们突出到低密度染色质区域。在这些区域，在体内以及细胞固定后的原位观察到DSB焦点的聚集（接触或融合）。这些聚集焦点中的大多数在240分钟内得到修复，但其中一些在照射后几天仍持续存在于细胞核中，表明存在不易修复的损伤。我们认为，聚集焦点中DSB的修复可能导致末端错接，进而导致交换畸变。另一方面，持续数天未修复的焦点可能反而导致细胞死亡。
