Mahadev K, Vemuri M C
School of Life Sciences, University of Hyderabad, India.
Neurochem Res. 1998 Sep;23(9):1179-84. doi: 10.1023/a:1020778018149.
Changes in chromatin conformation and nonhistone nuclear protein composition were analyzed in various classes of nuclei from the brain of control and chronic ethanol fed rats. Conformational studies of chromatin by circular dichroism spectrophotometry showed an increased molar ellipticity [theta] of chromatin in neuronal, astrocyte and oligodendroglial nuclei due to ethanol treatment. The increased molar ellipticity directly indicates relaxed state of chromatin in these nuclei, which facilitates ready state of transcription and replication. Further, the circular dichroism spectrum, due to a change over point at approximately 260 nm also indicated the possibility of DNA-protein interactions governing chromatin conformation. In microglial nuclei, the circular dichroism spectrum showed a decrease in molar ellipticity due to ethanol treatment, indicating the existence of chromatin in a condensed state. This type of circular dichroism change points towards the possibility of closed conformation, which renders the gene sequences not accessible due to conformational constrains of the chromatin. Since circular dichroism changes indicated the involvement of DNA-protein interactions, changes in nonhistone nuclear proteins were analyzed in these classes of nuclei by two-dimensional gel electrophoresis. In astrocytes and oligodendrocytes two new proteins appeared in each type of nuclei while in neurons and microglial nuclei four different proteins were either completely missing or showed a decrease. These changes indicate the presence of dynamic flux of nonhistone nuclear proteins in chromatin. Taken together, the changes in chromatin conformation, associated with specific changes in non histone nuclear protein composition suggest the modulation of chromatin as a response to ethanol evoked stimulus and has relevance in the regulation of cellular responses to ethanol crisis in brain.
在对照大鼠和长期喂食乙醇的大鼠大脑的各类细胞核中，分析了染色质构象和非组蛋白核蛋白组成的变化。通过圆二色光谱法对染色质进行的构象研究表明，由于乙醇处理，神经元、星形胶质细胞和少突胶质细胞核中的染色质摩尔椭圆率[θ]增加。摩尔椭圆率的增加直接表明这些细胞核中染色质处于松弛状态，这有利于转录和复制的就绪状态。此外，由于在约260nm处有一个转变点，圆二色光谱也表明存在DNA-蛋白质相互作用来控制染色质构象。在小胶质细胞核中，由于乙醇处理，圆二色光谱显示摩尔椭圆率降低，表明染色质处于浓缩状态。这种类型的圆二色性变化表明存在封闭构象的可能性，由于染色质的构象限制，使得基因序列无法接近。由于圆二色性变化表明涉及DNA-蛋白质相互作用，因此通过二维凝胶电泳分析了这些类型细胞核中非组蛋白核蛋白的变化。在星形胶质细胞和少突胶质细胞中，每种类型的细胞核中都出现了两种新蛋白质，而在神经元和小胶质细胞核中，四种不同的蛋白质要么完全缺失，要么含量降低。这些变化表明染色质中存在非组蛋白核蛋白的动态通量。综上所述，染色质构象的变化与非组蛋白核蛋白组成的特定变化相关，表明染色质作为对乙醇诱发刺激的反应受到调节，并且与大脑中细胞对乙醇危机的反应调节有关。
