综述: 表观遗传之染色质重塑

真核细胞中的染色质重塑因子种类繁多,多数以蛋白多聚体的形式存在于细胞中．不同的染色质重塑因子在特定时间定位于特定的核小体上,通过改变染色质结构,影响基因转录活性,进而确保细胞内各种生物学过程的正确运行．另外,染色质重塑因子根据所含功能结构域的不同,大致分为SWI/SNF、ISWI、CHD和INO80四大家族,不同的染色质重塑因子之间既有蛋白质结构和酶活性的相似性,各自又有其特异性．本综述的宗旨在于全面概括和总结染色质重塑因子的分类、结构特点以及其在细胞内的生物学功能,为深入研究染色质重塑因子的生物学功能,尤其是在发育和疾病发生中的作用机制提供理论基础．     

Causes and Consequences of the DNA Damage Response

A prerequisite for maintaining genome stability in all cell types is the accurate repair and efficient signaling of DNA double strand breaks (DSBs). It is believed that DSBs are initially detected by damage sensors that trigger the activation of transducing kinases. These transducers amplify the damage signal, which is then relayed to effector proteins, which regulate the progression of the cell cycle, DNA repair and apoptosis. Errors in the execution of the repair and/or signaling of DSBs can give rise to multi-systemic disorders characterized by tissue degeneration, infertility, immune system dysfunction, age-related pathologies and cancer. This special Spotlight issue of Cell Cycle highlights recent advances in our understanding of the biology and significance of the DNA damage response. A range of issues are addressed including mechanistic ones: what is the aberrant DNA structure that triggers the activation of the checkpoint - how does chromatin structure influence the recruitment of repair and checkpoint proteins- how does chromosomal instability contribute to the evolution of cancer. In addition, questions related to the physiology of the DNA damage response in normal and abnormal cells is explored: what is the in vivo consequence of altering specific amino acids in a DNA damage sensor- does DNA damage accumulation in stem cells cause aging- how is neurodegeneration linked to deficiencies in specific DNA repair pathways, and finally, what is the biological basis for selection of aberrant DNA damage responses in cancer cells?     

DNA Methylation is Reduced in DNasel-Sensitive Regions of Plant Chromatin

Pea, barley, and corn chromatin was isolated and subjected to limited digestion with DNasel. The preferentially degraded, small molecular weight fraction, presumably consisting of sequences in an active state of expression, was isolated and its 5-methylcytosine content determined. The DNasel-sensitive chromatin fraction from all three plant species investigated contained a markedly reduced level of DNA methylation compared to total DNA.