Reversible hypercondensation and decondensation of mitotic chromosomes studied using combined chemical-micromechanical techniques
Reversible hypercondensation and decondensation of mitotic chromosomes studied using combined chemical-micromechanical techniques
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DOI：
10.1002/jcb.10132
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发表时间：
2002-01-01
影响因子：
4
通讯作者：
Marko, JF
中科院分区：
文献类型：
--
作者：
Poirier, MG;Monhait, T;Marko, JF
我们表明，在有丝分裂染色体的染色质可以大大过度压缩或展开的离子浓度的临时变化。通过从微米大小的移液管中局部“微喷雾”反应物，同时监测单个染色体的大小和张力，我们能够定量研究这些反应的动力学。通过观察和校准用于操作染色体的玻璃移液管的弯曲来监测染色体中的张力。对于浓度> 500 mM的NaCl和> 200 mM的MgCl 2，我们发现最初施加的类似于500 pN的张力松弛至零，并且有丝分裂染色质暂时分散，与先前的工作一致（Maniotis等人[1997] J. Cell. 65：114-130）。这种解折叠发生在约1 s，是可逆的，一旦电荷密度恢复到生理水平，如果暴露时间不超过类似于1 min。低浓度的NaCl（< 30 mM）也诱导张力降低和尺寸增加。我们观察到这种肿胀是各向同性的实验中的染色体在零张力下，一个行为不一致的存在一个明确的中央染色体“支架”。相比之下，10 mM的二价阳离子（MgCl 2和CaCl 2）诱导张力的非常快速和可逆的增加，并减少有丝分裂染色体的大小。六氨合钴盐（三价阳离子）具有与MgCl 2和CaCl 2相同的效果，除了力增加和尺寸变化的幅度大得多。六氨合钴还原剂使有丝分裂染色体的体积减少到原来的65%，这表明它们的表观体积至少有1/3是水溶液。这些结果表明，有丝分裂染色单体内的染色质具有大量的构象自由，允许动态展开和重折叠，电荷相互作用在维持有丝分裂染色体结构中发挥着核心作用。J.细胞。85：422-434，2002. (C)2002 Wiley-Liss，Inc.
We show that the chromatin in mitotic chromosomes can be drastically overcompacted or unfolded by temporary shifts in ion concentrations. By locally 'microspraying' reactants from micron-size pipettes, while simultaneously monitoring the size of and tension in single chromosomes, we are able to quantitatively study the dynamics of these reactions. The tension in a chromosome is monitored through observation and calibration of bending of the glass pipettes used to manipulate the chromosomes. For concentrations > 500 mM of NaCl and > 200 mM of MgCl2, we find that the initially applied tensions of similar to500 pN relax to zero and that mitotic chromatin temporarily disperses in agreement with previous work (Maniotis et aL [1997] J. Cell. Biochem. 65:114-130). This unfolding occurs in about 1 s, and is reversible once the charge density is returned to physiological levels, if the exposure is not longer than similar to1 min. Low concentrations of NaCl (< 30 mM) also induces a decrease in tension and increase in size. We observe this swelling to be isotropic in experiments on chromosomes under zero tension, a behavior inconsistent with the existence of a well-defined central chromosome 'scaffold'. By contrast 10 mM of divalent cations (MgCl2 and CaCl2) induces an extremely rapid and reversible increase in tension and a reduction in the size of mitotic chromosomes. Hexaminecobalt trichloride (trivalent cation) has the same effect as MgCl2 and CaCl2, except the magnitude of force increase and size change are much larger. Hexaminecobalt trichloride reduces mitotic chromosomes to 65% of their original volume, indicating that at least 1/3 of their apparent volume is aqueous solution. These results indicate that chromatin inside mitotic chromatids has a large amount of conformational freedom allowing dynamic unfolding and refolding and that charge interactions play a central role in maintaining mitotic chromosome structure. J. Cell. Biochem. 85: 422-434, 2002. (C) 2002 Wiley-Liss, Inc.