Kokileva L
Bulgarian Academy of Sciences, Institute of Molecular Biology, Sofia.
Comp Biochem Physiol B Biochem Mol Biol. 1995 May;111(1):35-43. doi: 10.1016/0305-0491(94)00233-k.
A common strongly ordered multi-step-pattern of endogenous DNA degradation was induced in rat liver nuclei and intact thymocytes, prepared in the presence of chelating agents and incubated in the presence of CaCl2 and/or MgCl2. It consisted of sequential generation of 0.3 Mbp, then 0.05 Mbp DNA fragments and finally of oligo- and mononucleosomal DNA. Oligonucleosomal DNA was generated when the genome had already been disintegrated into 0.05 Mbp DNA fragments. ZnCl2 completely inhibited advanced genome cleavage to oligo- and mononucleosomal DNA without affecting the initial generation of large DNA fragments. Therefore, the endonucleolytic activity which produce large DNA fragments is different from Ca2+/Mg2+ endonuclease. The similar pattern of DNA degradation was observed in thymocytes treated with dexamethasone and with the topoisomerase II inhibitor VM-26, the agents known to induce apoptosis. The effect of VM-26 strongly suggests the involvement of topoisomerase II in generation of large DNA fragments. Multi-level organization and regulation of the chromatin structure determine the stepwise process of genome degradation. Detachment of chromatin from the nuclear matrix attachment regions may be one of the possible mechanisms of switching off the genome function and triggering the multi-step process of endogenous chromatin degradation thus leading to cell death in terminal differentiation or stress-induced apoptosis.
在存在螯合剂的情况下制备，并在氯化钙和/或氯化镁存在下孵育的大鼠肝细胞核和完整胸腺细胞中，诱导出了一种常见的内源性DNA降解的强有序多步模式。它包括依次产生0.3 Mbp、然后0.05 Mbp的DNA片段，最后是寡核小体和单核小体DNA。当基因组已经分解成0.05 Mbp的DNA片段时，就会产生寡核小体DNA。氯化锌完全抑制了基因组向寡核小体和单核小体DNA的进一步切割，而不影响大DNA片段的初始产生。因此，产生大DNA片段的核酸内切酶活性不同于Ca2+/Mg2+核酸酶。在用已知可诱导凋亡的地塞米松和拓扑异构酶II抑制剂VM-26处理的胸腺细胞中，观察到了类似的DNA降解模式。VM-26的作用强烈表明拓扑异构酶II参与了大DNA片段的产生。染色质结构的多层次组织和调节决定了基因组降解的逐步过程。染色质从核基质附着区域的脱离可能是关闭基因组功能和触发内源性染色质降解多步过程从而导致终末分化或应激诱导凋亡中细胞死亡的可能机制之一。
