A closer look at long-range chromosomal interactions

Higher-order chromosome organization is emerging as a major determinant of gene regulation. Although the structure of chromatin at the level of individual nucleosomes has been studied in considerable detail, less is known about higher levels of organization. Two new methods have been developed that can be used to obtain detailed information about the higher-order folding of chromatin. Using these methods, long-range looping interactions have been shown to occur upon activation of the murine beta-globin locus, explaining the long-standing question of how gene regulatory elements can act at large genomic distances from their target genes.     

Imprinting and looping: epigenetic marks control interactions between regulatory elements

Gene regulation involves various cis-regulatory elements that can act at a distance. They may physically interact each other or with their target genes to exert their effects. Such interactions are beginning to be uncovered in the imprinted Igf2/H19 domain.(1) The differentially methylated regions (DMRs), containing insulators, silencers and activators, were shown to have physical contacts between them. The interactions were changeable depending on their epigenetic state, presumably enabling Igf2 to move between an active and a silent chromatin domain. The study gives us a novel view on how regulatory elements influence gene expression and how epigenetic modifications modulate their long-range effects.     

人与小鼠核糖体蛋白基因内含子中的转录调控位点分析

前期对酵母和果蝇核糖体蛋白(Ribosomal protein, RP)基因内含子序列中的寡核苷酸分析表明, 内含子中含有潜在的转录因子结合位点。为进一步发掘核糖体蛋白基因内含子参与转录调控的证据, 文章首先基于频率分析方法抽提出人和小鼠核糖体蛋白基因第一内含子中高频(Over-represented)出现的寡核苷酸片段 (亦称模体, Motif), 这些寡核苷酸中超过85%与已知的转录因子结合位点吻合, 是潜在的转录调控元件。对抽提出的寡核苷酸进行碱基组成分析, 发现95%以上的寡核苷酸富含碱基C和G, 而较少富含A和T。从寡核苷酸在内含子中的分布情况看, 它们相对靠近第一内含子的5′端, 即距离基因转录起始位点和上游区域较近。推测这些特征可能与基因转录调控有关。