Immunobiochemical evidence for the loss of sperm specific histones during male pronucleus formation in monospermic zygotes of sea urchins

To obtain information on the remodeling of sperm chromatin during male pronuclei formation, we have followed the sperm specific histones (SpH) that form the nucleosomal core by Western immunoblot analysis with polyclonal antibodies directed against the core SpH. The results obtained indicate that the complete set of SpH is absent from zygote chromatin at the beginning of the first S phase. The disappearance of SpH is not coincidental for the five histone classes: SpH4 and SpH3 are lost 5-15 min post insemination (p.i.), SpH2B and SpH2A disappear 20-40 min p.i., and SpH1 is progressively diminished up to 30 min p.i. This order of sperm chromatin remodeling is not affected by the inhibition of protein synthesis by emetine, indicating that the factor(s) responsible for SpH disappearance are present in unfertilized eggs. The lost SpH's are not replaced by newly synthesized CS variants, since the basic proteins synthesized de novo during male pronuclei formation are not incorporated into chromatin remaining in the cytoplasm. These newly synthesized proteins are different from the CS variants as judged by their electrophoretic migration.     

Nucleosome positioning and gene regulation

Recent genetic and biochemical studies have revealed critical information concerning the role of nucleosomes in eukaryotic gene regulation. Nucleosomes package DNA into a dynamic chromatin structure, and by assuming defined positions in chromatin, influence gene regulation. Nucleosomes can serve as repressors, presumably by blocking access to regulatory elements; consequently, the positions of nucleosomes relative to the location of cis-acting elements are critical. Some genes have a chromatin structure that is “preset,” ready for activation, while others require “remodeling” for activation. Nucleosome positioning may be determined by multiple factors, including histone–DNA interactions, boundaries defined by DNA structure or protein binding, and higher-order chromatin structure. © 1994 Wiley-Liss, Inc.     

ATP依赖的染色质改构复合物及其作用机制

染色质高度紧密的折叠阻止了转录因子和辅因子与DNA的结合, 因而通过染色质重塑以解除这样的抑制环境, 对于转录活动的正常进行是至关重要的。目前认为, 染色质重塑至少是通过两种机制来完成的, 一种是通过ATP依赖的染色质改构复合物, 另一种是通过对组蛋白尾部进行共价修饰的组蛋白修饰酶复合物。文章结合近年来的研究进展, 对前者进行染色质重塑的机制及两者在基因转录调控过程中如何相互协作等进行了论述。     

丝状真菌中纤维素酶与半纤维素酶的合成调控简

综述了丝状真菌合成纤维素酶和半纤维素酶的相关调控研究进展。对最近研究文章分析发现：细胞外信号分子（C源、光信号）,转录因子以及染色质重建等对丝状真菌合成调控纤维素酶及半纤维素酶有重要影响。同时解析丝状真菌合成纤维素酶和半纤维素酶调控网络,以期为利用基因工程改造纤维素酶和半纤维素酶生产工业菌株提供理论指导。     

染色质结构与珠蛋白基因表达调控

综述了β－珠蛋白基因表达调控中,与染色质结构调控相关的区域,染色质重组复合体,染色质修饰等因素及它们之间协同作用的研究。     

依赖ATP的染色质物理修饰

染色质重塑是基因表达调控过程中一个非常重要的环节 .染色质重塑主要包括 2种类型 :一种是依赖ATP的物理修饰 ,另一种是依赖共价结合反应的化学修饰 .依赖ATP的物理修饰主要是利用ATP水解释放的能量 ,使DNA超螺旋旋矩和旋相发生变化 ,使转录因子更易接近并结合核小体DNA ,从而调控基因的转录过程     

Reaction cycle of the yeast Isw2 chromatin remodeling complex

Members of the ISWI family of chromatin remodeling factors hydrolyze ATP to reposition nucleosomes along DNA. Here we show that the yeast Isw2 complex interacts with DNA in a nucleotide-dependent manner at physiological ionic strength. Isw2 efficiently binds DNA in the absence of nucleotides and in the presence of a nonhydrolyzable ATP analog. Conversely, ADP promotes the dissociation of Isw2 from DNA. In contrast, Isw2 remains bound to mononucleosomes through multiple cycles of ATP hydrolysis. Solution studies show that Isw2 undergoes nucleotide-dependent alterations in conformation not requiring ATP hydrolysis. Our results indicate that during an Isw2 remodeling reaction, hydrolysis of successive ATP molecules coincides with cycles of DNA binding, release, and rebinding involving elements of Isw2 distinct from those interacting with nucleosomes. We propose that progression of the DNA-binding site occurs while nucleosome core contacts are maintained and generates a force dissipated by disruption of histone-DNA interactions.     

DNA methylation, nucleosome formation and positioning.

Recent mapping of nucleosome positioning on several long gene regions subject to DNA methylation has identified instances of nucleosome repositioning by this base modification. The evidence for an effect of CpG methylation on nucleosome formation and positioning in chromatin is reviewed here in the context of the complex sequence-structure requirements of DNA wrapping around the histone octamer and the role of this epigenetic mark in gene repression.     

雷帕霉素诱导β-珠蛋白家族基因座位重塑调控该基因的转换表达

β-珠蛋白基因编码异常导致的β-地中海贫血是许多亚洲国家最常见的血红蛋白病。深入研究珠蛋白基因表达的分子基础和表观遗传机制,是探索治疗地中海贫血新方案的关键。本研究利用FAIRE、3C及ChIP等主要技术方法,探讨雷帕霉素诱导CD4⁺T细胞核内染色质重塑过程中,β-珠蛋白家族基因座位的三维相互作用网络及其重塑在功能上调控基因表达的分子机制。结果显示,雷帕霉素处理浓度从低到高的变化过程中,珠蛋白基因染色质的开放程度、基因启动子区与调控元件LCR之间的相互作用频率以及CTCF在基因启动子区的富集效率发生不同的改变,这种变化导致了基因表达模式也呈现相同的变化趋势。10 nmol/L浓度处理时,染色质可及性降低,基因表达下降(P<0.05);20 nmol/L和50 nmol/L浓度时,染色质可及性增加,基因表达上调(P<0.05)。本研究通过这种动态的变化过程阐述了β-珠蛋白家族基因表达转换调控的分子机制,为临床精准治疗提供了理论与临床实践基础。