Continuous protein synthesis in nuclei,shown by radioautography with H3-labeled amino acids

Radioautographic investigation of the cell nuclei of adult mice after injection of leucine-H(3), methionine-H(3), or glycine-H(3) shows a high uptake of tritium by chromatin material but not by nucleoli. It is concluded that protein synthesis occurs continuously within nuclear chromatin.     

Roles of NPM2 in chromatin and nucleolar organization in oocytes and embryos

Upon fertilization, remodeling of condensed maternal and paternal gamete DNA occurs to form the diploid genome. In Xenopus laevis, nucleoplasmin 2 (NPM2) decondenses sperm DNA in vitro. To study chromatin remodeling in vivo, we isolated mammalian NPM2 orthologs. Mouse NPM2 accumulates in oocyte nuclei and persists in preimplantation embryos. Npm2 knockout females have fertility defects owing to failed preimplantation embryo development. Although sperm DNA decondensation proceeds without NPM2, abnormalities are evident in oocyte and early embryonic nuclei. These defects include an absence of coalesced nucleolar structures and loss of heterochromatin and deacetylated histone H3 that normally circumscribe nucleoli in oocytes and early embryos, respectively. Thus, Npm2 is a maternal effect gene critical for nuclear and nucleolar organization and embryonic development.     

Dynamics of single mRNPs in nuclei of living cells

Understanding gene expression requires the ability to follow the fate of individual molecules. Here we use a cellular system for monitoring messenger RNA (mRNA)expression to characterize the movement in real time of single mRNA-protein complexes (mRNPs) in the nucleus of living mammalian cells. This mobility was not directed but was governed by simple diffusion. Some mRNPs were partially corralled throughout the nonhomogenous nuclear environment, but no accumulation at subnuclear domains was observed. Following energy deprivation, energy-independent motion of mRNPs was observed in a highly ATP-dependent nuclear environment; movements were constrained to chromatin-poor domains and excluded by newly formed chromatin barriers. This observation resolves a controversy, showing that the energetic requirements of nuclear mRNP trafficking are consistent with a diffusional model.     

Structural organization of nuclei and nucleoli of wheat shoot and root meristem during germination under alkaline pH conditions

The state of the nuclear compartment of winter wheat shoot and root meristem during germination under high pH value conditions is analyzed. An increase in the number of amoeboid nucleoli having protuberances, disturbance of chromatin compaction, and occurrence of nuclear bodies of unknown etiology in apical meristem are noted.     

桑蚕幼虫中肠细胞腺苷三磷酸酶活性的细胞化学

用电镜细胞化学技术研究了桑蚕五龄幼虫中肠组织细胞中ＡＴＰａｓｅ的亚细胞分布。ＡＴＰａｓｅ仅大量分布在中肠圆筒形细胞的微绒毛和杯形细胞在肠腔的开口处、肠壁肌肉的肌质膜上、部分细胞的细胞质膜和细胞器及细胞质中．ＡＴＰａｓｅ的这种分布状态与细胞的功能紧密相关．     

The importance of threading dislocations on the motion of domain boundaries in thin films

Thin films often present domain structures whose detailed evolution is a subject of debate. We analyze the evolution of copper films, which contain both rotational and stacking domains, on ruthenium. Real-time observation by low-energy electron microscopy shows that the stacking domains evolve in a seemingly complex way. Not only do the stacking boundaries move in preferred directions, but their motion is extremely uneven and they become stuck when they reach rotational boundaries. We show that this behavior occurs because the stacking-boundary motion is impeded by threading dislocations. This study underscores how the coarse-scale evolution of thin films can be controlled by defects.     

Visualizing chromatin dynamics in interphase nuclei

Real-time fluorescence microscopy has emerged as a powerful tool for examining chromatin dynamics. The initial lesson is that much of the genome, particularly in yeast, is highly dynamic. Its movement within the interphase nucleus is correlated with metabolic activity. Nonetheless, the nucleus is an organelle with conserved rules of organization. Determining the distribution and regulation of mobile domains in interphase chromosomes, and characterizing sites of anchorage, will undoubtedly shed new light on the function of nuclear order.     

微小泰泽球虫小配子发育的超微结构

采用纯种微小泰泽球虫卵囊,人工感染四日龄雏鹅,定时剖杀,取小肠组织进行超薄切片,在透射电镜下,观察微小泰泽球虫小配子体与小配子的超微结构和发育过程。小配子体由第二代裂殖子发育而来。当小配子体完成最后一次核分裂后,其核中染色质呈斑块状,核内无核仁。随后,细胞核移向小配子体边缘,并拉长成二部分,电子致密部分将发育成小配子的核,电子密度浅的另一部分则留在残体中。每个细胞核上方有一对中心粒,中心粒将进一步发育成为小配子两根鞭毛的基粒,鞭毛由此产生。成熟的小配子拥有两根鞭毛和一个体部,体部有一个长形的细胞核,核的前面嵌有一线粒体。     

Chromosomal and nucleolar RNA synthesis in root tips during mitosis

Comparative rates of RNA synthesis in chromatin and nucleolar fractions during mitosis in root-tip cells of Allium and Nigella were studied by pulse-labeling of cells with tritiated cytidine. Although the rate of RNA synthesis decreases in the condensing chromosomes during prophase, it remains normal in the nucleolar fraction as long as nucleoli are maintained. RNA synthesis stops in mitotic cells lacking distinct nucleoli. In the late telophase or very early interphase cells, RNA synthesis resumes at a faster rate in the pronucleolar bodies than in the chromatin.     

The bacterial flagellar cap as the rotary promoter of flagellin self-assembly

The growth of the bacterial flagellar filament occurs at its distal end by self-assembly of flagellin transported from the cytoplasm through the narrow central channel. The cap at the growing end is essential for its growth, remaining stably attached while permitting the flagellin insertion. In order to understand the assembly mechanism, we used electron microscopy to study the structures of the cap-filament complex and isolated cap dimer. Five leg-like anchor domains of the pentameric cap flexibly adjusted their conformations to keep just one flagellin binding site open, indicating a cap rotation mechanism to promote the flagellin self-assembly. This represents one of the most dynamic movements in protein structures.     

The maternal nucleolus is essential for early embryonic development in mammals

With fertilization, the paternal and maternal contributions to the zygote are not equal. The oocyte and spermatozoon are equipped with complementary arsenals of cellular structures and molecules necessary for the creation of a developmentally competent embryo. We show that the nucleolus is exclusively of maternal origin. The maternal nucleolus is not necessary for oocyte maturation; however, it is necessary for the formation of pronuclear nucleoli after fertilization or parthenogenetic activation and is essential for further embryonic development. In addition, the nucleolus in the embryo produced by somatic cell nuclear transfer originates from the oocyte, demonstrating that the maternal nucleolus supports successful embryonic development.     

Ultrastructural organization of the domains in the cell nucleus of dicotyledonous and monocotyledonous plants under abiotic stress

The transformation of the structural organization of interphase nuclei of a plant cell, depending on the type of tissue, ploidy, and the action of abiotic factors of the medium, has been studied by light and transmission electron microscopy. It is shown that the location and the quantitative relationship between condensed and decondensed chromatin, the presence and localization of nuclear bodies in the plant nucleus, and the presence of invaginations of the nuclear membrane and inclusions depend on the tissue type and cell age as well as the intensity, time, and type of exposure to abiotic factors. Examples of different degrees of chromatin condensation in one plant organism are given. It has been established that the degree of chromatin condensation and decondensation, the state of other domains and nonspecific inclusions of the cell nucleus can be artificially modeled for research purposes or subsequent modification. The issue of application of such technologies for the creation and selection of stable forms of agricultural plants taking into account the controlled modification of their genome is discussed. A possible mechanism for incorporation of nonspecific inclusions in a nuclear compartment is proposed.     

日本鹌鹑睾丸的电镜观察

本文是通过透射电镜观察日本鹌鹑(Coturnix coturnix japonica)雄性生殖细胞及间质细胞的超微结构。精原细胞呈椭圆形。核圆形,异染色质少,常呈小块状,多靠近核被膜,核仁明显。染色质周围颗粒及染色质间颗粒清晰可见。线粒体有时呈空泡状,嵴短而稀疏,均匀分布于胞质中。精母细胞的异染色质散在分布于核质中,由颗粒状物质聚成团块,核仁明显。线粒体数量不多,分布情况如精原细胞。这与鸡的线粒体分布位置存有差异。粗面内质网和高尔基复合体发育良好,并可见环孔板。精子细胞核大而圆,异染色质少,呈稀疏的颗粒状分布在核被膜附近及分散于核液中。线粒体电子密度较高,内质网及高尔基复合体发育中等。间质细胞形状不规則,核仁清晰,内质网及线粒体丰富,二者有极性分布现象。线粒体嵴既有小管状,又有板层状。     

A reversible synthetic rotary molecular motor

The circumrotation of a submolecular fragment in either direction in a synthetic molecular structure is described. The movement of a small ring around a larger one occurs through positional displacements arising from biased Brownian motion that are kinetically captured and then directionally released. The sense of rotation is governed solely by the order in which a series of orthogonal chemical transformations is performed. The minimalist nature of the [2]catenane flashing ratchet design permits certain mechanistic comparisons with the Smoluchowski-Feynman ratchet and pawl. Even when no work has to be done against an opposing force and no net energy is used to power the motion, a finite conversion of energy is intrinsically required for the molecular motor to undergo directional rotation. Nondirectional rotation has no such requirement.     

Identification of a second dynamic state during stick-slip motion

Stick-slip, or interrupted, motion rather than smooth uninterrupted motion occurs in many different phenomena such as friction, fluid flow, material fracture and wear, sound generation, and sensory "texture." During stick-slip, a system is believed to undergo transitions between a static (solid-like) state and a kinetic (liquid-like) state. The stick-slip motion between various types of pretreated surfaces was measured, and a second, much more kinetic state that exhibits ultra-low friction was found. Transitions to and from this super-kinetic state also give rise to stick-slip motion but are fundamentally different from conventional static-kinetic transitions. The results here suggest practical conditions for the control of unwanted stick-slip and the attainment of ultra-low friction.