大鼠老化过程大脑皮层及小脑神经元染色质构象分析

Analysis of Chromatin Conformation in the Cerebral Cortex and Cerebellum Neurons During Rat Aging

本文在前文~[2]的基础上进一步以MCN和DNaseⅠ为探针研究大鼠脑神经元终末分化后不同生理时期染色质构象,结果表明:<l>MCN酶解DNA产物PAGE显示脑老化过程大脑皮层及小脑神经元染色质核小体单体DNA分别保持在176bp和215bp水平,核小体连接DNA长度存在组织差异,但不受老化影响;<2>DNaseⅠ酶解DNA产物PAGE显示各年龄组大脑皮层及小脑神经元染色质DNA存在10bp间隔重复结构和相同的泳动区带分布特征,提示脑老化中染色质具有稳定的B型双螺旋结构和一致的螺线管卷曲形式。染色质DNaseⅠ降解率随年龄增加而降低,提示老化导致活性染色质区域减少,老化过程脑神经元染色质构象改变成为其转录功能减退的结构基础。

Male rats of different ages (4-, 16-17-, 33-34- and 99-103-week) were studied. By using endonucleases (MCN and DNase I ) as probe to study changes of chromatin conformation in neurons from these animals,H was showed that the neuronal chromatin in cerebral cortex and cerebellum had a repeat length (nucleosome core and linker region) of 176 bp and 215 bp respectively, regardless of the age of rats. The DNA length of nucleosome core was 140 bp in both neuronal populations. These indicated there were no aging-related changes in the neuronal nucleosome spacing.Analysis of DNA fragments produced by DNase I on PAGE showed that DNase I cleaved neuronal nucleosome DNA at 10 bp intervals and the cleavage patterns were the same in all ages of rats. The characteristic of the PAGE patterns, in which a weak band at 60 nucleotides(NT) and an intense one at 80 NT were observed, were identical either in different neurons or in ages of rats, it means the chromatin DNA mainly existed in B type of duplex conformation and contained similiar superhelical structure of solenoid in cerebral cortex and cerebellum neurons during rat aging. However, comparison of DNA fragments produced by DNase J in young and old rats showed that less fragments with lower base pair were produced in old rats,it probably due to the aging-induced decline of transcribing regions in the neuronal chromatin.