Ribosomal RNA synthesis and the multiple, atypical nucleoli in cleaving embryos

The rate of ribosomal RNA synthesis per nucleus in cleaving sea urchin embryos is similar to the rate at later embryonic stages. The multiple, atypical nucleoli, present in early embryos and usually attributed to decreased ribosomal RNA synthesis, are beginning stages of nucleolar formation. Full nucleolar development requires more time than the brief interphase of the rapidly dividing cells.     

6-Methylpurine-H3: intracellular localization in pea root tip cells

6-Methylpurine-H3, a potent inhibitor, was detected by autoradiography in the nucleoli of pea root tip cells. Most of the radioactivity was in the nucleoli of growing cells in the meristematic region. Treatment of the labeled cells with ribonuclease indicates that 6-methylpurine-H(3) is incorporated into nucleolar RNA which then moves from the nucleolus to the cytoplasm.     

Ribosomal RNA synthesis and processing in a particulate site in the HeLa cell nucleus

A particulate fraction has been isolated from detergent-prepared HeLa cell nuclei. The fraction consists largely of organelles that resemble the nucleoli of intact cells. The 45S RNA that is precursor to 28S and 18S ribosomal RNA is associated with the fraction. The 32S RNA that is labeled after the 45S RNA and is the apparent precursor to 28S RNA is also associated with the fraction. The nucleoplasm contains 28S RNA that behaves as an intermediate between the 32S nucleolar RNA and the 28S cytoplasmic RNA.     

Biosynthesis and composition of histones in Novikoff hepatoma nuclei and nucleoli

Histones were prepared from isolated nuclei and nucleoli of the Novikoff ascitic hepatoma at several time points after the injection of L-lysine uniformly labeled with C(14) into tumor-bearing rats. Amino acid analysis and starch-gel electrophoresis failed to reveal any differences between the nuclear and nucleolar histones, although both fractions were more acidic in composition than calf thymus histones. However, the nucleolar histones were a metabolically distinct fraction, and their rate of synthesis was approximately twice that of the total nuclear histones.     

Effect of the Vinca alkaloids on RNA synthesis in human cells in vitro

The Vinca alkaloids vinblastine sulfate and vincrystine sulfate, which are mitotic poisons, inhibit RNA synthesis in human (HEp-2) cells cultured in vitro. Analyses of RNA synthesis by cells treated with these drugs by acrylamide gel electrophoresis show that 28s rRNA and to a lesser extent 18s rRNA are preferentially inhibited. The synthesis of tRNA is affected much less than that of rRNA. The present experiments suggest that the drugs inhibit both the synthesis and processing of the nucleolar RNA precursors of rRNA. An explanation is also given for previous reports that these alkaloids preferentially inhibit the synthesis of tRNA in animal cells in vitro.     

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.     

棉花和小叶杨小孢子母细胞中超数核仁的形成及动态变化

用光镜和透射电镜观察研究了棉花(Gossypium hirsutum)和小叶杨(Populussimonii)小孢子母细胞中超数核仁的发生和动态变化过程。超数核仁出现于减数分裂前(棉花)和减数分裂前期Ⅰ早期(小叶杨),产生部位是核仁组织者区域。超数核仁与主核仁有类似的染色特性,但体积小,数量丰富。在小孢子母细胞减数分裂过程中,超数核仁通过下述主要方式进入细胞质:一是在分裂中期和后期核膜暂时解体时进入细胞质中;另一是在核膜完整时通过状态的变化经核膜孔进入细胞质或以整体形式通过核膜外突并缢出进入细胞质中。小孢子母细胞中超数核仁的发生可能是大量迅速补给细胞质核糖体数量的一种机制,与孢子体转向配子体的发育有关。     

Actinomycin D; renewed RNA synthesis after removal from mammalian cells

Suppressed RNA synthesis exceeded control rates 2 hours after removal of actinomycin from serial lines of green monkey kidney cells in exponentially dividing monolayer cultures. Enhanced synthesis was directly related to the dose of actinomycin, and release from inhibition was temperature dependent. A broad range of RNA sizes was made after removal of drug, but cytoplasmic and nucleolar sedimentation profiles were abnormal for at least 20 hours.     

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.     

Ribosomal RNA synthesis during cleavage of Ascaris lumbricoides eggs

The appearance of well-defined nucleoli in 4-celled Ascaris embryos is associated with the synthesis of ribosomal RNA.     

Visualization of nucleolar genes

The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules. Visualization of these genes is possible because many precursor molecules are simultaneously synthesized on each gene. Individual genes are separated by stretches of DNA that apparently are not transcribed at the time of synthesis of precursor rRNA in the extrachromosomal nucleoli.     

Synthesis of 5S and 4S RNA in metaphase-arrested HeLa cells

The continued synthesis of both 5S and 4S RNA in metaphase-arrested HeLa cells is demonstrated; 5S RNA is apparently synthesized at approximately 74 percent of the interphase rate, while 4S RNA is synthesized at approximately one-third the rate. The ratio of uridine incorporation to RNA methylation is used to correct for the alteration in the specific activity of the pyrimidine pool during metaphase arrest.     

Curvilinear, three-dimensional motion of chromatin domains and nucleoli in neuronal interphase nuclei

The term "nuclear rotation" refers to a motion of nucleoli within interphase nuclei of several cell types. No mechanism or function has been ascribed to this phenomenon, and it was unknown whether nuclear structures in addition to nucleoli participate in this motion. Moreover, it was unclear whether nuclear rotation occurs independent of concurrent motion of juxtanuclear cytoplasm. The work reported here presents quantitative evidence, for three-dimensional intranuclear, tandem motion of fluorescently labeled chromatin domains associated with nucleoli and those remote from nucleoli. The results show that such motion is curvilinear, that it is not restricted to nucleoli, and, moreover, that it occurs independently of motion of juxtanuclear, cytoplasmic structures. These results suggest that this motion represents karyoplasmic streaming and its function is to transpose to nuclear pores those chromatin domains actively transcribed.     

Activation of the DNA replication checkpoint through RNA synthesis by primase

When DNA replication is inhibited during the synthesis (S) phase of the cell cycle, a signaling pathway (checkpoint) is activated that serves to prevent mitosis from initiating before completion of replication. This replication checkpoint acts by down-regulating the activity of the mitotic inducer cdc2-cyclin B. Here, we report the relation between chromatin structure and induction of the replication checkpoint. Chromatin was competent to initiate a checkpoint response only after the DNA was unwound and DNA polymerase alpha had been loaded. Checkpoint induction did not require new DNA synthesis on the unwound template strand but did require RNA primer synthesis by primase. These findings identify the RNA portion of the primer as an important component of the signal that activates the replication checkpoint.     

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.     

水产养殖环境胁迫对鱼类表观遗传的影响研究进展

表观遗传学是研究基因核苷酸序列不发生改变的情况下,基因表达的可遗传的变化的一门遗传学分支学科。表观遗传的现象较多,已有DNA甲基化、组蛋白修饰、染色质重塑、非编码RNA调控、基因组印记、基因沉默、母体效应、核仁显性、休眠转座子激活等。在集约化的水产养殖模式中,养殖密度提高,投喂过量等均会产生刺激鱼类生长的环境因素。已有文献报道,环境胁迫因素刺激可影响鱼类表观遗传修饰,但并未涉及遗传信息的变化,所以在一定范围内可以解释为表型变化。本研究围绕环境胁迫因素对鱼类表观遗传产生的影响进行了综述,为进一步阐释环境因素与基因互作关系提供了参考。     

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．     

Small nuclear RNA U2 is base-paired to heterogeneous nuclear RNA

Eukaryotic cells contain a set of low molecular weight nuclear RNA's. One of the more abundant of these is termed U2 RNA. The possibility that U2 RNA is hydrogen-bonded to complementary sequences in other nuclear RNA's was investigated. Cultured human (HeLa) cells were treated with a psoralen derivative that cross-links RNA chains that are base-paired with one another. High molecular weight heterogeneous nuclear RNA was isolated under denaturing conditions, and the psoralen cross-links were reversed. Electrophoresis of the released RNA and hybridization with a human cloned U2 DNA probe revealed that U2 is hydrogen-bonded to complementary sequences in heterogeneous nuclear RNA in vivo. In contrast, U2 RNA is not base-paired with nucleolar RNA, which contains the precursors of ribosomal RNA. The results suggest that U2 RNA participates in messenger RNA processing in the nucleus.