Strong nucleosomes reside in meiotic centromeres of C. elegans

Recently discovered strong nucleosomes (SNs) are characterized by strongly periodical DNA sequence, with visible rather than hidden sequence periodicity. In a quest for possible functions of the SNs, it has been found that the SNs concentrate within centromere regions of A. thaliana chromosomes . They, however, have been detected in Caenorhabditis elegans as well, although the holocentric chromosomes of this species do not have centromeres. Scrutinizing the SNs of C. elegans and their distributions along the DNA sequences of the chromosomes, we have discovered that the SNs are located mainly at the ends of the chromosomes of C. elegans. This suggests that, perhaps, the ends of the chromosomes fulfill some function(s) of centromeres in this species, as also indicated by the cytogenetic studies on meiotic chromosomes in spermatocytes of C. elegans, where the end-to-end association is observed. The centromeric involvement of the SNs, also found in A. thaliana, opens new horizons for the chromosome and centromere structure studies.     

Efficient isolation of specific genomic regions and identification of associated proteins by engineered DNA-binding molecule-mediated chromatin immunoprecipitation (enChIP) using CRISPR

Isolation of specific genomic regions retaining molecular interactions is necessary for their biochemical analysis. Here, we established a novel method, engineered DNA-binding molecule-mediated chromatin immunoprecipitation (enChIP), for purification of specific genomic regions retaining molecular interactions. We showed that enChIP using the CRISPR system efficiently isolates specific genomic regions. In this form of enChIP, specific genomic regions are immunoprecipitated with antibody against a tag(s), which is fused to a catalytically inactive form of Cas9 (dCas9), which is co-expressed with a guide RNA (gRNA) and recognizes endogenous DNA sequence in the genomic regions of interest. enChIP–mass spectrometry (enChIP–MS) targeting endogenous loci identified associated proteins. enChIP using the CRISPR system would be a convenient and useful tool for dissecting chromatin structure of genomic regions of interest.     

30 nm染色质的体外组装和电镜分析

真核生物的基因组以染色质的形式存在,染色质在真核生物的基因表达调控及胚胎发育过程中起重要作用,为表观遗传提供一个重要的信息整合平台．染色质的高级结构,特别是 30 nm染色质的动态变化在基因转录沉默和激活过程中起着重要的调控功能．但是目前对30 nm 染色质纤维的组装及其精细结构的认识还十分有限．本文通过体外表达系统,表达未经修饰的组蛋白,并利用克隆构建的601DNA均一重复序列,通过逐步降低盐离子浓度并加入组蛋白H1或镁离子的方法,体外重组均一的30 nm染色质纤维．并利用镀金属、负染色制样和冷冻电镜制样等手段通过透射式电子显微镜(TEM)对30 nm纤维结构的形成原因、组蛋白H1的作用和核小体重复单位(nucleosome repeat lengths,NRLs)长度对30 nm染色质纤维的影响进行研究．研究结果显示在组蛋白H1或二价镁离子存在的情况下,均可形成30 nm染色质纤维．其形成的染色质拓扑结构有所不同．统计分析表明,不同长度核小体重复单位(NRLs)形成的染色质纤维直径有所不同(P < 0.05)．同时,我们得到了较为均一的冷冻电镜样品,为进一步研究30 nm染色质纤维的高级结构及理解体内染色质存在的形式及动态过程打下了较好的基础．     

Dietary Resistant Starch Reduces Histone Acetylation on the Glucose-Dependent Insulinotropic Polypeptide Gene in the Jejunum

We have reported that dietary resistant starch (RS) reduces glucose-dependent insulinotropic polypeptide (GIP) mRNA levels along the jejunoileum in both normal and diabetic rats. In this study, we found that jejunal reduction of the GIP gene by feeding normal rats dietary RS was associated with decreases in histone H3 and H4 acetylation on the promoter/enhancer region of the gene.