植物着丝粒区串联重复序列的研究进展

着丝粒是细胞染色体的重要结构组成,控制姊妹染色单体的结合、动粒的组装和纺锤丝的附着,确保真核生物细胞在有丝分裂和减数分裂过程中染色体的正常分离及遗传信息的稳定传递。植物着丝粒DNA序列主要由反转录转座子和串联重复序列构成。串联重复序列在着丝粒功能实现和基因组进化过程中起重要作用。随着测序技术的成熟,近年来对串联重复序列的研究取得了很大的进展。综述了植物串联重复序列结构、分析方法及在进化中的作用,以期为相关研究提供参考。     

Genomic and genetic definition of a functional human centromere

The definition of centromeres of human chromosomes requires a complete genomic understanding of these regions. Toward this end, we report integration of physical mapping, genetic, and functional approaches, together with sequencing of selected regions, to define the centromere of the human X chromosome and to explore the evolution of sequences responsible for chromosome segregation. The transitional region between expressed sequences on the short arm of the X and the chromosome-specific alpha satellite array DXZ1 spans about 450 kilobases and is satellite-rich. At the junction between this satellite region and canonical DXZ1 repeats, diverged repeat units provide direct evidence of unequal crossover as the homogenizing force of these arrays. Results from deletion analysis of mitotically stable chromosome rearrangements and from a human artificial chromosome assay demonstrate that DXZ1 DNA is sufficient for centromere function. Evolutionary studies indicate that, while alpha satellite DNA present throughout the pericentromeric region of the X chromosome appears to be a descendant of an ancestral primate centromere, the current functional centromere based on DXZ1 sequences is the product of the much more recent concerted evolution of this satellite DNA.     

着丝粒特异组蛋白CENH3的研究及应用

着丝粒特异组蛋白CENH3是较早被发现的一种基本蛋白,存在于真核生物的功能着丝粒中,是功能着丝粒染色质最基本的特征。CENH3在进化上比较快速,其氨基末端尾巴和组蛋白质折叠域都具有变异性,在着丝粒的组装及染色体的正常分离与传递中起着关键作用。该文主要围绕CENH3的发现及进化、结构与功能及应用展开综述。     

Requirement of heterochromatin for cohesion at centromeres

Centromeres are heterochromatic in many organisms, but the mitotic function of this silent chromatin remains unknown. During cell division, newly replicated sister chromatids must cohere until anaphase when Scc1/Rad21-mediated cohesion is destroyed. In metazoans, chromosome arm cohesins dissociate during prophase, leaving centromeres as the only linkage before anaphase. It is not known what distinguishes centromere cohesion from arm cohesion. Fission yeast Swi6 (a Heterochromatin protein 1 counterpart) is a component of silent heterochromatin. Here we show that this heterochromatin is specifically required for cohesion between sister centromeres. Swi6 is required for association of Rad21-cohesin with centromeres but not along chromosome arms and, thus, acts to distinguish centromere from arm cohesion. Therefore, one function of centromeric heterochromatin is to attract cohesin, thereby ensuring sister centromere cohesion and proper chromosome segregation.     

Requirement of Mis6 centromere connector for localizing a CENP-A-like protein in fission yeast

Mammalian kinetochores contain the centromere-specific histone H3 variant CENP-A, whose incorporation into limited chromosomal regions may be important for centromere function and chromosome segregation during mitosis. However, regulation of CENP-A localization and its role have not been clear. Here we report that the fission yeast homolog SpCENP-A is essential for establishing centromere chromatin associated with equal chromosome segregation. SpCENP-A binding to the nonrepetitious inner centromeres depended on Mis6, an essential centromere connector protein acting during G1-S phase of the cell cycle. Mis6 is likely required for recruiting SpCENP-A to form proper connection of sister centromeres.     

Two histone marks establish the inner centromere and chromosome bi-orientation

For proper partitioning of chromosomes in mitosis, the chromosomal passenger complex (CPC) including Aurora B and survivin must be localized at the center of paired kinetochores, at the site called the inner centromere. It is largely unknown what defines the inner centromere and how the CPC is targeted to this site. Here, we show that the phosphorylation of histone H3-threonine 3 (H3-pT3) mediated by Haspin cooperates with Bub1-mediated histone 2A-serine 121 (H2A-S121) phosphorylation in targeting the CPC to the inner centromere in fission yeast and human cells. H3-pT3 promotes nucleosome binding of survivin, whereas phosphorylated H2A-S121 facilitates the binding of shugoshin, the centromeric CPC adaptor. Haspin colocalizes with cohesin by associating with Pds5, whereas Bub1 localizes at kinetochores. Thus, the inner centromere is defined by intersection of two histone kinases.     

高等植物着丝粒序列的结构与特征研究

着丝粒是染色体的重要组成成分之一,在细胞有丝分裂和减数分裂中行使重要的生物学功能,着丝粒在不同的物1种中保持着一致的功能,即在细胞分裂中期,着丝粒在纺锤丝的牵引下使染色体向两级运动,从而完成细胞的分裂。如此保守的功能,是乎暗示着丝粒序列不同物种间具有一定的保守性,然而随着测序技术的发展,越来越多的物种的基因组序列被释放,分析发现着丝粒序列主要由重复序列和反转录转座子组成,然而不同物种着丝粒序列比对发现,它们之间的同源性极低,此外染色体的着丝粒的序列的组成和大小都相差甚远。文中回顾了近些年在着丝粒研究方面所取得的进展,探讨维持着丝粒功能稳定性的序列结构特征。     

植物着丝粒的研究进展

着丝粒是许多高等真核生物染色体的重要结构域之一,它的最内层是由串联重复的卫星DNA及其侧翼富集的中度重复元件组成。在整个真核生物类群中,不同物种间着丝粒的DNA序列千差万别,但其功能却相当保守,可确保在有丝分裂和减数分裂过程中染色体的正确分离和传递。近年来,植物着丝粒的结构、功能和进化方面的研究进展较快,故对此进行了综述。     

Gene for von Recklinghausen neurofibromatosis is in the pericentromeric region of chromosome 17

Linkage analysis of 15 Utah kindreds demonstrated that a gene responsible for von Recklinghausen neurofibromatosis (NF) is located near the centromere on chromosome 17. The families also gave no evidence for heterogeneity, indicating that a significant proportion of NF cases are due to mutations at a single locus. Further genetic analysis can now refine this localization and may lead to the eventual identification and cloning of the defective gene responsible for this disorder.     

Centromere: absence of DNA replication during chromatid separation in human fibroblasts

Cultures of human fibroblasts were labeled briefly with tritiated thymidine and fixed; autoradiographs were made and exposed for 3(1/2) months. No labeling was noted over the centromere of metaphase or anaphase chromosomes. The technique was sensitive to replication at the centromere of a DNA helix only 2.5 microns long, considerably shorter than the estimated length of a replicon in humans. This suggests that chromatid separation during mitosis is not associated with delayed replication of a short segment of chromosomal DNA.     

Factors affecting early embryonic development in cattle: relevance for bovine cloning

Female infertility represents a major challenge for improving the production efficiency in the dairy industry. Historically, fertility has declined whereas milk yield has increased tremendously due to intensive genetic selection. In vivo evidence reveals about 60% pregnancy loss takes place during the first month following fertilization. Meanwhile, early embryo development is significant for somatic cell nuclear transfer in cattle as a large proportion of cloned embryos fail to develop beyond peri-implantation stage. Oocyte quality is of utmost importance for the early embryo to develop to term for both fertilized and cloned embryos. Epigenetic reprogramming is a key process occurring after fertilization and critical roles of epigenetic modifiers during preimplantation development are now clear. Incomplete epigenetic reprogramming is believed to be a major limitation to cloning efficiency. Treatment of cloned embryos with epigenetic modifying drugs (e.g., Trichostatin A) could greatly improve cloning efficiency in both mice and cattle. Recently, the rapid progress in high-throughput sequencing technologies has enabled detailed deciphering of the molecular mechanisms underlying these events. The robust efficiency of genomic editing tools also presents an alternative approach to the functional annotation of genes critical to early development.     

木薯中性/碱性转化酶基因家族11个成员在染色体上的定位

中性/碱性转化酶(Alkaline or neutral invertase,N/A-lnv)是木薯淀粉合成过程中的一种关键酶。笔者以木薯华南6号古铜期嫩叶为材料制备染色体标本,利用荧光原位杂交和原位PCR技术对N/A-lnv基因家族的11个成员进行了物理定位。结果表明,基因MeNINV5,MeNINV9和MeNINV10均位于第4号染色体上,其中基因MeNINV9和MeNINV10位于短臂上,到信号点的百分距离分别为68.52和95.35,基因MeNINV5位于长臂上,到着丝粒的百分距离为22.71;基因MeNINV4和nINV1均位于第6号染色体长臂上,到着丝粒的百分距离分别为43.16和80.71;基因MeNINV6和MeNINV7分别位于第7号和第17号染色体的长臂上,信号点到着丝粒的百分距离分别是15.38和57.97;基因MeNINV1,MeNIN,V2,MeNINV3和MeNINV8分别位于第11号、第9号、第5号和第16号染色体的短臂上,信号位点到着丝粒的百分距离分别是40.10,51.88,91.75和76.33。中性/碱性转化酶基因家族内部部分成员之间存在连锁关系。研究结果可为木薯淀粉的高效积累机制及木薯种质遗传改良提供分子细胞遗传学依据。     

Role of histone H3 lysine 9 methylation in epigenetic control of heterochromatin assembly

The assembly of higher order chromatin structures has been linked to the covalent modifications of histone tails. We provide in vivo evidence that lysine 9 of histone H3 (H3 Lys9) is preferentially methylated by the Clr4 protein at heterochromatin-associated regions in fission yeast. Both the conserved chromo- and SET domains of Clr4 are required for H3 Lys9 methylation in vivo. Localization of Swi6, a homolog of Drosophila HP1, to heterochomatic regions is dependent on H3 Lys9 methylation. Moreover, an H3-specific deacetylase Clr3 and a beta-propeller domain protein Rik1 are required for H3 Lys9 methylation by Clr4 and Swi6 localization. These data define a conserved pathway wherein sequential histone modifications establish a "histone code" essential for the epigenetic inheritance of heterochromatin assembly.     

旱地春小麦籽粒碳同位素分辨率及冠层温度与产量的关系

[目的]探讨小麦冠层温度和叶绿素含量替代碳同位素分辨率（CID）进行抗旱育种的可靠性.[方法]以抗旱性不同的5个春小麦品种为材料,测定正常灌溉和干旱处理的籽粒CID、开花期与灌浆中期的冠层温度以及旗叶叶绿素含量指数,并分析这些指标与籽粒产量的关系.[结果]在干旱、灌水条件下,籽粒CID均与产量显著正相关（P≤0.01）;灌浆中期的冠层温度在干旱条件下与籽粒CID显著负相关（P≤0.05）,但在灌水条件下与后者相关不明显,开花期的冠层温度在2种条件下与籽粒产量及CID均无明显相关;在2种处理下,旗叶叶绿素含量与CID均无明显相关.[结论]灌浆中期的冠层温度仅在干旱条件下可以替代籽粒CID进行抗旱品种选育,而在干旱和灌水条件下开花期冠层温度和旗叶叶绿素含量均不能用作籽粒CID的替代指标.     

A histone acetyltransferase regulates active DNA demethylation in Arabidopsis

Active DNA demethylation is an important part of epigenetic regulation in plants and animals. How active DNA demethylation is regulated and its relationship with histone modification patterns are unclear. Here, we report the discovery of IDM1, a regulator of DNA demethylation in Arabidopsis. IDM1 is required for preventing DNA hypermethylation of highly homologous multicopy genes and other repetitive sequences that are normally targeted for active DNA demethylation by Repressor of Silencing 1 and related 5-methylcytosine DNA glycosylases. IDM1 binds methylated DNA at chromatin sites lacking histone H3K4 di- or trimethylation and acetylates H3 to create a chromatin environment permissible for 5-methylcytosine DNA glycosylases to function. Our study reveals how some genes are indicated by multiple epigenetic marks for active DNA demethylation and protection from silencing.     

Vernalization-mediated epigenetic silencing by a long intronic noncoding RNA

Vernalization is an environmentally-induced epigenetic switch in which winter cold triggers epigenetic silencing of floral repressors and thus provides competence to flower in spring. In Arabidopsis, winter cold triggers enrichment of tri-methylated histone H3 Lys(27) at chromatin of the floral repressor, FLOWERING LOCUS C (FLC), and results in epigenetically stable repression of FLC. This epigenetic change is mediated by an evolutionarily conserved repressive complex, polycomb repressive complex 2 (PRC2). Here, we show that a long intronic noncoding RNA [termed COLD ASSISTED INTRONIC NONCODING RNA (COLDAIR)] is required for the vernalization-mediated epigenetic repression of FLC. COLDAIR physically associates with a component of PRC2 and targets PRC2 to FLC. Our results show that COLDAIR is required for establishing stable repressive chromatin at FLC through its interaction with PRC2.