真菌中DNA重复序列诱导点突变的研究进展

1987年,由Selker等在粗糙脉孢菌中首次发现重复序列诱导点突变(repeat-induced point mutation,RIP).在重复序列诱导点突变过程中,搜寻前减数分裂组织单倍体核中DNA的重复序列,然后发生众多的碱基C到T的突变,产生富碱基T+A片段,从而使重复序列中的G-C碱基对发生转换突变成为A-T碱基对.此外,发生RIP的序列多集中在着丝粒区域,主要是转座子甲基化后的遗迹.移动转座子是真核生物基因组进化的主要驱动力.对于真菌,重复序列诱导点突变(RIP)在减数分裂过程中通过突变多拷贝DNA,能最大限度地减少转座子的影响,因此对RIP的研究在一定程度上能有助于了解基因组进化的真谛.综述了重复序列诱导点突变的产生机制,以及真菌中重复序列诱导点突变的研究进展.     

着丝粒与动粒的功能、结构和动态组装（英文）

确保真核生物物种的遗传信息在亲代与子代之间忠实地传递是细胞有丝分裂的一项基本任务。着丝粒是一个特殊的染色体区域，对于在有丝分裂过程中介导姐妹染色单体的排列和分离至关重要。着丝粒身份确定是由含有着丝粒蛋白A(CENP-A)的核小体这种表观遗传机制决定的。CENP-A核小体为有丝分裂期内层动粒和外层动粒组装的关联提供了基础。本文回顾了着丝粒身份确定、内层动粒功能和组装以及外层动粒功能和组装。特别是，我们关注了组成型着丝粒关联网络（CCAN）结构活性关系的最新进展。CCAN结构信息为我们对着丝粒和动粒功能以及动态组装的理解提供了新的启示。     

野生－粒小麦着丝粒RCS1相关序列的克隆鉴定

用水稻着丝粒重复序列RCS1为探针，与3072个克隆进行菌落杂交，得到了32个阳性克隆，用RCS1与拟斯卑尔脱山羊草着丝粒重复序列Tcs250为探针进一步筛选，在32个RCS1相关的阳性克隆中任选10个克隆进行点杂交，分别有6个和5个阳性克隆．为了克隆RCS1相关片段，依据RCS1的序列设计了三对引物，将引物3从上述阳性克隆中扩增的一个543bp的片段克隆测序，发现与水稻RCS1部分片段达到约83％的同源，与大麦的反转座子(Ty3／gypsy)部分序列同源性达到了92％，与节节麦中着丝粒的整合酶基因部分序列同源性达到了96％，命名为TBRCS1．TBRCS1可能是野生一粒小麦着丝粒区的组成部分．     

着丝粒串联重复序列RCS2对亚洲栽培稻和非洲栽培稻的比较分析

为了揭示中高度重复序列在同为AA基因组的亚洲栽培稻和非洲栽培稻基因组中的差异以及重复序列在.栽培稻种的分化过程中可能起到的作用,利用水稻着丝粒串联重复序列RCS2作为探针分别对籼稻广陆矮4号、粳稻日本晴和非洲栽培稻的体细胞染色体进行荧光原位杂交(FISH)实验,并对其核型进行同源性聚类和比较分析,杂交结果显示:RCS2序列位于在3种栽培稻染色体组中,RCS2序列位于每条染色体的着丝粒位置,但有不同的分布特点,表明该3种栽培稻基因组的RCS2序列有不同的进化方向.探讨了RCS2序列结合Cot-1 DNA FISH方法对水稻染色体组进行核型分析的可行性和优势.     

不同物种间胰岛素及其编码mRNA,DNA序列比较与分析

通过PSI-BLAST搜索与人类胰岛素原(含有86个氨基酸)相似的蛋白质序列，并进行比对，计算比对矩阵的相似得分和期望值，同时运用ClustalW算法对不同物种编码前胰岛素原mRNA及其翻译的蛋白质和DNA序列进行多重比对．结果发现，脊椎动物的胰岛素蛋白质一级结构(A链和B链)和mRNA非常相似，但部分动物C肽的部分序列有差异；系统进化分析表明，人和猴、小鼠和大鼠编码胰岛素的mRNA在进化上关系相近．各物种间编码相同氨基酸的核苷酸序列（CDS)相同，但编码胰岛素的DNA序列不同．各物种胰岛素原蛋白质序列中，A链和B链序列保守，C肽有一定的差异；DNA序列差异较大．     

DNA指纹图技术及其在实验动物学中的应用

实验动物要求具有明确的遗传背景 ,实验动物的遗传质量直接影响生物医学研究结果的准确性、重复性与科学性 ,遗传质量监测是保证实验动物遗传质量的重要措施[1] 。现在实验动物的遗传质量监测运用生化标记等表型检测方法 ,存在灵敏度低等局限性。随着分子生物学技术的发展 ,DNA分子标记技术的出现 ,为实验动物遗传物质DNA的直接检测带来了新的可行的技术方法。1　DNA指纹技术的原理真核生物的基因组大且复杂 ,广泛分布着各种形式的重复序列 ,由于它们不编码肽链 ,很少受到自然选择作用的影响而保持着高度的多态性。这些重复序列按其在染…     

DNA检测方法在鱼类物种鉴定中的应用

总结了近年来在鱼类物种鉴定中常用的DNA序列分析、DNA指纹技术、物种特异性聚合酶链式反应和实时荧光PCR技术等DNA检测方法,同时对各类方法的特点和局限性进行了分析．     

鱼类线粒体DNA控制区的结构和进化：以BangPi鱼类为例

以Bang Pi鱼类为例，研究了鱼类线粒体DNA控制区的结构和进化规律。识别了终止序列区、中央保守区和保守序列区3个区域。指出扩展终止相关序列（ETAS）的主体是TACAT和它的反向互补序列ATGTA形成的发夹结构。给出了鱼类中若干重要保守序列的普遍形式。研究结果表明，一般情况下，只有一个行使功能的ETAS，但可能会有多个复制的、不行使功能的ETAS存在。鱼类的保守序列CSB2最为保守。线粒体DNA控制区被认为是由各功能单位形成主体框架，主体框架复制产生重复序列，重复序列产生快速变异，这样造成不同类群间线粒体DNA控制区巨大差异。易突变点和二级结构的存在均可能与变异的发生相关。     

分子标记及AFLP技术

分子标记类型可以基因表达的结果为基础,对基因的间接反映;分子标记则是DNA分子碱基序列变异的直接反映.早期利用限制性内切酶,酶切生物体DNA后来检测不同遗传位点等位变异(RFLP)和以一个碱基顺序随机排列的寡核苷酸序列为引物,利用对基因组DNA随机扩增来鉴别DNA多态性(RAPDs).真核生物基因组中普遍存在的重复序列产生了微卫星(microsatellites)标记技术.而RFLP与RAPDs有机结合形成了有着更为广阔的应用前景的AFLP技术.SNP标记利用大多数基因位点上都会有若干个等位型(alleles)为DNA芯片技术应用于遗传作图提供了基础.     

端粒酶与食管癌、胃癌相关性的研究

端粒是染色体DNA端部的特化部分，由高度重复的短序列DNA一蛋白质组成的特殊结构，能维持染色体的稳定和完整．端粒酶是由RNA与蛋白质亚基组成的核糖核蛋白酶，能以自身RNA为模板，合成端粒序列，是一种非常特殊的逆转录酶．端粒的长度和端粒酶的活性与细胞永生化，细胞衰老和癌变密切相关，在肿瘤发生发展中，端粒酶成为一种重要的肿瘤生物学标志物，有望作为诊断和治疗肿瘤的新靶点．本对端粒酶的结构与功能，端粒酶与食管癌、胃癌相关性的研究新进展及端粒酶活性的检测方法做一简要综述．     

Microtubule-motor activity of a yeast centromere-binding protein complex.

During cell division, sister chromosomes segregate from each other on a microtubule-based structure called the mitotic spindle. Proteins bind to the centromere, a region of chromosomal DNA, to form the kinetochore, which mediates chromosome attachment to the mitotic spindle microtubules. In the budding yeast Saccharomyces cerevisiae, genetic analysis has shown that the 28-basepair (bp) CDEIII region of the 125-bp centromere DNA sequence (CEN sequence) is the main region controlling chromosome segregation in vivo. Therefore it is likely that proteins binding to the CDEIII region link the centromeres to the microtubules during mitosis. A complex of proteins (CBF3) that binds specifically to the CDEIII DNA sequence has been isolated by affinity chromatography. Here we describe kinetochore function in vitro. The CBF3 complex can link DNA to microtubules, and the complex contains a minus-end-directed microtubule-based motor. We suggest that microtubule-based motors form the fundamental link between microtubules and chromosomes at mitosis.     

The Ph1 locus is needed to ensure specific somatic and meiotic centromere association

The correct pairing and segregation of chromosomes during meiosis is essential for genetic stability and subsequent fertility. This is more difficult to achieve in polyploid species, such as wheat, because they possess more than one diploid set of similar chromosomes. In wheat, the Ph1 locus ensures correct homologue pairing and recombination. Although clustering of telomeres into a bouquet early in meiosis has been suggested to facilitate homologue pairing, centromeres associate in pairs in polyploid cereals early during floral development. We can now extend this observation to root development. Here we show that the Ph1 locus acts both meiotically and somatically by reducing non-homologous centromere associations. This has the effect of promoting true homologous association when centromeres are induced to associate. In fact, non-homologously associated centromeres separate at the beginning of meiosis in the presence, but not the absence, of Ph1. This permits the correction of homologue association during the telomere-bouquet stage in meiosis. We conclude that the Ph1 locus is not responsible for the induction of centromere association, but rather for its specificity.     

Structural determinants for generating centromeric chromatin

Mammalian centromeres are not defined by a consensus DNA sequence. In all eukaryotes a hallmark of functional centromeres--both normal ones and those formed aberrantly at atypical loci--is the accumulation of centromere protein A (CENP-A), a histone variant that replaces H3 in centromeric nucleosomes. Here we show using deuterium exchange/mass spectrometry coupled with hydrodynamic measures that CENP-A and histone H4 form sub-nucleosomal tetramers that are more compact and conformationally more rigid than the corresponding tetramers of histones H3 and H4. Substitution into histone H3 of the domain of CENP-A responsible for compaction is sufficient to direct it to centromeres. Thus, the centromere-targeting domain of CENP-A confers a unique structural rigidity to the nucleosomes into which it assembles, and is likely to have a role in maintaining centromere identity.     

The genome of the social amoeba Dictyostelium discoideum

The social amoebae are exceptional in their ability to alternate between unicellular and multicellular forms. Here we describe the genome of the best-studied member of this group, Dictyostelium discoideum. The gene-dense chromosomes of this organism encode approximately 12,500 predicted proteins, a high proportion of which have long, repetitive amino acid tracts. There are many genes for polyketide synthases and ABC transporters, suggesting an extensive secondary metabolism for producing and exporting small molecules. The genome is rich in complex repeats, one class of which is clustered and may serve as centromeres. Partial copies of the extrachromosomal ribosomal DNA (rDNA) element are found at the ends of each chromosome, suggesting a novel telomere structure and the use of a common mechanism to maintain both the rDNA and chromosomal termini. A proteome-based phylogeny shows that the amoebozoa diverged from the animal-fungal lineage after the plant-animal split, but Dictyostelium seems to have retained more of the diversity of the ancestral genome than have plants, animals or fungi.     

Heterochromatin links to centromeric protection by recruiting shugoshin

The centromere of a chromosome is composed mainly of two domains, a kinetochore assembling core centromere and peri-centromeric heterochromatin regions. The crucial role of centromeric heterochromatin is still unknown, because even in simpler unicellular organisms such as the fission yeast Schizosaccharomyces pombe, the heterochromatin protein Swi6 (HP1 homologue) has several functions at centromeres, including silencing gene expression and recombination, enriching cohesin, promoting kinetochore assembly, and, ultimately, preventing erroneous microtubule attachment to the kinetochores. Here we show that the requirement of heterochromatin for mitotic chromosome segregation is largely replaced by forcibly enriching cohesin at centromeres in fission yeast. However, this enrichment of cohesin is not sufficient to replace the meiotic requirement for heterochromatin. We find that the heterochromatin protein Swi6 associates directly with meiosis-specific shugoshin Sgo1, a protector of cohesin at centromeres. A point mutation of Sgo1 (V242E), which abolishes the interaction with Swi6, impairs the centromeric localization and function of Sgo1. The forced centromeric localization of Sgo1 restores proper meiotic chromosome segregation in swi6 cells. We also show that the direct link between HP1 and shugoshin is conserved in human cells. Taken together, our findings suggest that the recruitment of shugoshin is the important primary role for centromeric heterochromatin in ensuring eukaryotic chromosome segregation.     

An analysis of the gene expression of a centromere constitutive protein CenpG affected by antisense CenpB

By means of indirect immunofluorescence ( IIF), indirect immunofluorescence-flow cytometry ( IIF FCM ) and Western blot, the gene expression level and localization and distribution of CenpG in HeLa-Tet Off cell with the inhibition of the expression of CenpB were detected, and some problems related to cell proliferation were analyzed. The results show that, (1) affected by antisense CenpB, the indirect immunofluorescence of centromeres is weakened, with notable network like fluorescent material structure in the nuclei, and centromere number indicated by fluorescence is much less; (2) CenpG expresses less;(3) the CenpG antigenicity is inhibited by around 79%. It is suggested that the effects of anti-sense CenpB on CenpG are highly consistent to that on its own sense CenpB gene, disclosing the rather close relation between these two centromere proteins.     

Pre-meiotic S phase is linked to reductional chromosome segregation and recombination

Meiosis is initiated from G1 of the cell cycle and is characterized by a pre-meiotic S phase followed by two successive nuclear divisions. The first of these, meiosis I, differs from mitosis in having a reductional pattern of chromosome segregation. Here we show that meiosis can be initiated from G2 in fission yeast cells by ectopically activating the meiosis-inducing network. The subsequent meiosis I occurs without a pre-meiotic S phase and with decreased recombination, and exhibits a mitotic pattern of equational chromosome segregation. The subsequent meiosis II results in random chromosome segregation. This behaviour is similar to that observed in cells lacking the meiotic cohesin Rec8 (refs 3, 4), which becomes associated with chromosomes at G1/S phase, including the inner centromere, a region that is probably critical for sister-centromere orientation. If the expression of Rec8 is delayed to S phase/G2, then the centromeres behave equationally. We propose that the presence of Rec8 in chromatin is required at the pre-meiotic S phase to construct centromeres that behave reductionally and chromosome arms capable of a high level of recombination, and that this explains why meiosis is initiated from G1 of the cell cycle.     

三种国外冷杉的核型研究

首次报道了３种国外冷杉的核型。ＡｂｉｅｓｃｅｐｈａｌｏｎｉｃａＬｏｕｄ。有９对中部着丝粒和３对近中着丝粒染色体,Ａ．ｎｕｍｉｄｉｃａＤｅＬａｎｎｏｎｅｘＣａｒｒ．文中还讨论了３种冷杉及其氯不组的进化地位。     

The Karyotypes,C-banding Patterns and AgNORs of Epinephelus malabaricus

0　IntroductionThestudyonfishchromosomeswasstartedabroadinthethirtiesofthetwentiethcentury .Butduetoimperfectfixedmethodsandtechniques ,determinationwasstronglysubjective ,inadditionfishchromosomesbeingmuchsmallerthanthoseofhumanspeciesandothermammals ,plantsandinsects ,thereliabilityofearlyresearchresultswasratherdeviated .Afterthefifties ,thepreparation ,observationmethodsandtechniquesofhumanchromo someswereconstantlyimproved ,andin 1 970s ,variouschromosomebandingtechniqueswereestablished .…