小麦根端分生细胞间期集缩染色质银染蛋白的分析

小麦根端分生组织经整体银染色后在电子显微镜下观察看到，间期集缩染色质中分布有许多大小不等、数量各异的银染颗粒，这些银染颗粒形状的图象分析结果显示，大的银粒 状，小的银粒有的为点状，有的实际为短纤维状，这些结果表明：小麦间期集缩染色质中存在着非组蛋白性质的骨架结构，骨架蛋白以颗粒和纤维状的形式分布于整个集缩染色质中，最后对染色质骨架、染色体骨架和核基质之间的相互关系进行了讨论。     

小麦根端分生组织细胞内染色体/质上ATP酶活性的超微结构定位

本文采用磷酸铅沉淀的细胞化学方法，对小麦根端分生组织细胞内染色体上的ATPase活性进行了超微结构定位，结果显示：染色体上有大量ATPase的分布；同时还看到间期细胞核中染色质和核仁上ATPase的活性也很高．综合染色体／质的结构特点和ATPase在生命活动中的功能，作为染色体／质骨架的组成成分，ATPase除了与染色体／染色质在细胞周期中的动态变化密切相关外，可能还执行着一定的其它生物学功能。     

小麦根端分生组织细胞内染色体/质上ATP酶活性的超微结构定位

采用磷酸铅沉淀的细胞化学方法,对小麦根端分生组织细胞内染色体上的ATPase活性进行了超微结构定位,结果显示:染色体上有大量ATPase的分布;同时还看到间期细胞核中染色质和核仁上ATPase的活性也很高.综合染色体/质的结构特点和ATPase在生命活动中的功能,作为染色体/质骨架的组成成分,ATPase除了与染色体/染色质在细胞周期中的动态变化密切相关外,可能还执行着一定的其它生物学功能.     

圆锥小麦高亲和种质的C带分析

采用改良Ｃ带技术对圆锥小麦和高亲种质矮兰麦的根尖细胞染色体进行了分析，矮兰麦体细胞具１４对染色体，非同源染色体之间，带的大小，强弱和分布不同。矮兰麦２ＡＬ和７ＡＳ染色体臂及７Ｂ染色体的带型与野生二粒小麦不同；矮兰麦３Ｂ，４Ａ，４Ｂ及７Ｂ染色体与普通小麦相应染色体的带型也有判别。     

去除核酸和组蛋白的小麦染色体超微结构

去除核酸和组蛋白的小麦染色体在电镜下仍呈现出其基本形态．中期染色体结构致密，前期和晚中期染色体能区分出其两条姊妹染色单体，不过二者之间仍有很多物质相互交联，着丝粒连接着染色单体．由此我们认为：染色体中确实也存在着一种由非组蛋白蛋白质构成的、嗜银性很强的骨架结构，呈网络分布，它在维持染色体的形态以及在染色体的集缩包装中起重要作用．着丝粒是骨架的一部分．     

染色体高级结构模型及其分歧

染色体是遗传信息的载体,对其高级结构的研究是染色体结构研究的核心问题。由30nm的染色质基础纤维如何进一步构建染色体的高级结构尚有争议。本文综述了解释染色体高级结构的几种主要模型,包括纤维折叠模型、多级螺旋模型、骨架——放射环模型、辐射环和螺旋共存模型、等级螺旋模型等,并对模型的分歧及其产生的原因进行了分析。     

新发现的毛冠鹿的一核型与性染色体探讨

以原代培养和传代培养的方法培养成年雄性毛冠鹿的皮肤细胞,对其核型进行分析,发现了一种新的核型,二倍体染色体数为2n=48,染色体正好配成24对,其中有一对为异型染色体.该对异型染色体的一条为较大的端着丝粒染色体,长度仅次于第3号染色体,C带与薄层扫描显示其异染色质丰富.另一条为较大的近端着丝粒染色体,长度介于第2号与第3号染色体之间,比其他已知核型中相应的染色体长,几乎全为异染色质.G带分析表明该对异型染色体的异染色质区域均显示一些数目不等的浅带.本文通过核型分析,对毛冠鹿的性染色体进行了初步的探讨.     

“降落伞”核的演变和大核原基的发育

应用DAPI荧光染色术对冠突伪尾柱虫有性生殖过程中两种结构演化最复杂的核现象进行了观察。在“降落伞”的形成并向第一次成熟分裂中期转变期间,“伞盖”和“重物”染色质团之间自始至终由DNA荧光丝状物相联,“重物”染色质团随着“伞盖”部染色质丝缩短变粗而逐渐变小,并在中期染色体形成的同时消失。为解释上述演变过程,在讨论中提出了一个细胞学动态模型。在大核原基的发育过程中,于染色体多线化之前先由染色质丝转变为短杆状染色体。这些染色体移向核的一极,然后从一端开始解螺旋并向核的另一极伸展。在此期间,可以观察到某些染色体成双存在。     

小麦染色体配对基因Ph1结构剖析及调控机制研究进展

近年来,关于小麦抑制部分同源染色体配对基因Ph1的研究有了突破性进展.本文对该基因的结构和调控机理的最新研究进行综述.通过创造和分子标记鉴定Ph1缺失突变体,利用分子生物学及比较基因组学技术,该基因位点被界定于5BL上一个2.5 Mb的区域内,含有一个类cdk基因簇,且在该类cdk基因簇中插入一个亚端粒异染色质片段.细胞学研究显示,Ph1基因通过控制亚端粒的互作启始染色体识别和配对伙伴选择.与此同时,生物信息学揭示,这些类cdk基因与人类和老鼠的cdk2基因高度同源,它们与细胞周期中DNA复制、染色质凝集、碱基错配修复等事件相关.减数分裂时,该基因位点通过"感知"染色体的同源性程度而触发染色质的构象变化,从而控制染色体的配对和重组.此外,小麦中可能存在一种与Ph1相关的类似于酵母中的粗线期检查点机制.预测未来的研究将可能集中在Ph1对染色体同源性的"感知"机制、Ph1的开启与关闭、植物减数分裂重组的忠实性及减数分裂过程的检查点机制等方面.     

黑腹果蝇野生型及其突变型染色体C-带的研究

本文研究了黑腹果蝇的野生型及其几个突变型的C-带异染色质,测量了各染色体的相对长度和C-带的相对长度,结果表明,各突变型之间的C-带异染色质有多态现象。看来,这几个突变型性状表现不只是一个主基因的差异,在染色体C-带异染色质也有差异。     

Intranuclear injection of anti-actin antibodies into Xenopus oocytes blocks chromosome condensation

The role of contractile proteins in the structural organisation of the interphase nucleus and of metaphase chromosomes is largely unknown. Actin has been found in interphase nuclei of different species, especially in association with condensed chromatin. In the germinal vesicle (nucleus) of Xenopus oocytes, actin has been localised in the nuclear gel supporting the chromosomes and the extrachromosomal nucleoli. It has been reported that the premeiotic lampbrush chromosomes in these germinal vesicles are positively stained for actin and tubulin by the immunoperoxidase technique. Moreover, the longitudinal contraction of these chromosomes is ATP dependent. Therefore it has been suggested that actin participates in the structural organisation of the highly specialised lampbrush chromosomes. However, actin is not a major component of the metaphase chromosome scaffold. The results reported here suggest that actin is involved in the condensation of Xenopus chromosomes.     

Focal points for chromosome condensation and decondensation revealed by three-dimensional in vivo time-lapse microscopy

Although the dynamic behaviour of chromosomes has been extensively studied in their condensed state during mitosis, chromosome behaviour during the transition to and from interphase has not been well documented. Previous electron microscopic studies suggest that chromosomes condense in a non-uniform fashion at the nuclear periphery. But chromosome condensation is a complicated and dynamic process and requires continuous observation in living tissues to be fully understood. Using a recently developed three-dimensional time-lapse fluorescence microscopy technique, we have observed chromosomes as they relax from telophase, through interphase, until their condensation at the next prophase. This technique has been improved to produce higher-resolution images by implementing new stereographic projection and computational processing protocols. These studies have revealed that chromosomal regions on the nuclear envelope, distinct from the centromeres and telomeres, serve as foci for the decondensation and condensation of diploid chromosomes. The relative positions of the late decondensation sites at the beginning of interphase appear to correspond to the early condensation sites at the subsequent prophase.     

赖草PMC细胞融合现象的研究

文章报道了赖草(Leymusscaline)花粉母细胞(PMC)的细胞融合现象。结果表明,细胞融合主要发生在间期、终变期。间期发生细胞融合主要是细胞质转移,因此不会产生明显的遗传学效应。终变期细胞融合主要是染色体的迁移,其细胞遗传学效应主要是造成供体和受体细胞的染色体数目变化,从而产生了非整倍体配子。文章还对细胞融合产生的原因进行了讨论。     

Topological domains in mammalian genomes identified by analysis of chromatin interactions

The spatial organization of the genome is intimately linked to its biological function, yet our understanding of higher order genomic structure is coarse, fragmented and incomplete. In the nucleus of eukaryotic cells, interphase chromosomes occupy distinct chromosome territories, and numerous models have been proposed for how chromosomes fold within chromosome territories. These models, however, provide only few mechanistic details about the relationship between higher order chromatin structure and genome function. Recent advances in genomic technologies have led to rapid advances in the study of three-dimensional genome organization. In particular, Hi-C has been introduced as a method for identifying higher order chromatin interactions genome wide. Here we investigate the three-dimensional organization of the human and mouse genomes in embryonic stem cells and terminally differentiated cell types at unprecedented resolution. We identify large, megabase-sized local chromatin interaction domains, which we term 'topological domains', as a pervasive structural feature of the genome organization. These domains correlate with regions of the genome that constrain the spread of heterochromatin. The domains are stable across different cell types and highly conserved across species, indicating that topological domains are an inherent property of mammalian genomes. Finally, we find that the boundaries of topological domains are enriched for the insulator binding protein CTCF, housekeeping genes, transfer RNAs and short interspersed element (SINE) retrotransposons, indicating that these factors may have a role in establishing the topological domain structure of the genome.     

香雪兰染色体的Giemsa C显带研究

利用醋酸洋红 Giemsa—C 显带技术对香雪兰根尖细胞的染色体进行了显带研究。经过处理的染色体在前期和中期呈现各种较典型的 C 带带型,如端带、着丝点带和中间带,而且非同源染色体之间的带型差异较大。第五对同源染色体具有一对特大的端带,这对端带在间期呈现大型的染色中心。在同源染色体之间未发现带型的多态性现象,所以,利用香雪兰的 C 带带型特征,完全可以鉴定该基卧组中的同源染色体对。文章还讨论了有关间期核的染色中心数与分裂期染色体带的数目之间的关系等问题。     

Role of transposable elements in heterochromatin and epigenetic control

Heterochromatin has been defined as deeply staining chromosomal material that remains condensed in interphase, whereas euchromatin undergoes de-condensation. Heterochromatin is found near centromeres and telomeres, but interstitial sites of heterochromatin (knobs) are common in plant genomes and were first described in maize. These regions are repetitive and late-replicating. In Drosophila, heterochromatin influences gene expression, a heterochromatin phenomenon called position effect variegation. Similarities between position effect variegation in Drosophila and gene silencing in maize mediated by "controlling elements" (that is, transposable elements) led in part to the proposal that heterochromatin is composed of transposable elements, and that such elements scattered throughout the genome might regulate development. Using microarray analysis, we show that heterochromatin in Arabidopsis is determined by transposable elements and related tandem repeats, under the control of the chromatin remodelling ATPase DDM1 (Decrease in DNA Methylation 1). Small interfering RNAs (siRNAs) correspond to these sequences, suggesting a role in guiding DDM1. We also show that transposable elements can regulate genes epigenetically, but only when inserted within or very close to them. This probably accounts for the regulation by DDM1 and the DNA methyltransferase MET1 of the euchromatic, imprinted gene FWA, as its promoter is provided by transposable-element-derived tandem repeats that are associated with siRNAs.     

Domain organization of human chromosomes revealed by mapping of nuclear lamina interactions

The architecture of human chromosomes in interphase nuclei is still largely unknown. Microscopy studies have indicated that specific regions of chromosomes are located in close proximity to the nuclear lamina (NL). This has led to the idea that certain genomic elements may be attached to the NL, which may contribute to the spatial organization of chromosomes inside the nucleus. However, sequences in the human genome that interact with the NL in vivo have not been identified. Here we construct a high-resolution map of the interaction sites of the entire genome with NL components in human fibroblasts. This map shows that genome-lamina interactions occur through more than 1,300 sharply defined large domains 0.1-10 megabases in size. These lamina-associated domains (LADs) are typified by low gene-expression levels, indicating that LADs represent a repressive chromatin environment. The borders of LADs are demarcated by the insulator protein CTCF, by promoters that are oriented away from LADs, or by CpG islands, suggesting possible mechanisms of LAD confinement. Taken together, these results demonstrate that the human genome is divided into large, discrete domains that are units of chromosome organization within the nucleus.     

An extrachromosomal factor causing loss of paternal chromosomes

Extrachromosomal inheritance is ubiquitous among plants and animals; however, most extrachromosomal factors are uniparentally inherited through females, but not through males. Examples include chloroplasts, mitochondria and a variety of intracellular symbionts. The only known exception to maternal extrachromosomal inheritance in an animal is a paternally transmitted sex ratio factor (psr) which causes all-male families in the parasitic wasp, Nasonia vitripennis. Normally in this wasp, male offspring are haploid and develop from unfertilized eggs whereas females are diploid and develop from fertilized eggs. The psr factor is either a venereally transmitted infection which prevents egg fertilization (and therefore causes all-male families), or a factor transmitted to eggs by the sperm of males carrying psr, which somehow prevents incorporation of the paternal chromosomes. Here we report that sperm from psr males fertilizes eggs, but that the paternal chromosomes are subsequently condensed into a chromatin mass before the first mitotic division of the egg and do not participate in further divisions. Resulting haploid offspring are male, but have inherited the paternal factor. This extrachromosomal factor promotes its own transmission at the expense of the paternal chromosomes, and therefore can be considered a 'selfish' genetic element.