Gene structure and chromosomal localization of mouse cyclin G2 (Ccng2)

Cyclins are essential activators of cyclin-dependent kinases (Cdk) which, in turn, play pivotal roles in controlling transition through cell-cycle checkpoints. Cyclin G2 is a recently discovered second member of the G-type cyclins. The two members of the G-type cyclins, cyclin G1 and cyclin G2, share high structural similarity but their function remains to be defined. Here we characterize the structure of the mouse cyclin G2 gene by first cloning and sequencing the full-length mouse cyclin G2 cDNA. The cyclin G2 cDNA was used to isolate the cyclin G2 gene from a BAC library and to establish that the gene was transcribed from eight exons spanning a total of 8604 bp. The cyclin G2 gene was mapped by fluorescence in situ hybridization (FISH) to mouse chromosome 5E3.3.–F1.3. This region is syntenic to a region on human chromosome 4. The expression of cyclins G1 and G2 was examined in various tissues, but no correlation between expression patterns of the two genes was observed. However, during hepatic ontogenesis the cyclin G2 expression level decreased with age, whereas cyclin G1 expression increased. Transient expression of cyclin G2-green fluorescent protein (GFP) fusion protein in NIH3T3 cells showed that cyclin G2 is essentially a cytoplasmic protein, in contrast to the largely nuclear localization of cyclin G1. Our data suggest that, despite the close structural similarity between mouse cyclins G1 and G2, these proteins most likely perform distinct functions.     

稀土化合物氯化亚鈰对人肺癌细胞PG、人胃癌细胞BGC-823的作用

 以人肺癌细胞 Ｐ Ｇ 和人胃癌细胞 Ｂ Ｇ Ｃ ８２３ 作为研究对象,利用 Ｍ Ｔ Ｔ 测定、３ Ｈ Ｔｄ Ｒ 参入、流式细胞术、软琼脂培养、 Ｎｏｒｔｈｅｒｎ ｂｌｏｔ、 Ｗ ｓｔｅｒｎ ｂｌｏｔ 等实验方法,观察了稀土化合物氯化亚鈰（ Ｃｅ Ｃｌ３）抑癌作用．结果表明, Ｃｅ Ｃｌ３ 浓度为 ００５ ｍ ｍ ｏｌ／ Ｌ,０１ ｍ ｍ ｏｌ／ Ｌ,０５ ｍ ｍ ｏｌ／ Ｌ和 １ ｍ ｍ ｏｌ／ Ｌ可抑制 Ｐ Ｇ 细胞的增殖;浓度为 ０５ ｍ ｍ ｏｌ／ Ｌ和 １ ｍ ｍ ｏｌ／ Ｌ可抑制 Ｐ Ｇ 细胞 Ｄ Ｎ Ａ 的合成,其 Ｇ１ 期细胞比例增加而 Ｓ期细胞比例减少,在软琼脂中的生长能力降低,原癌基因 ｃ ｍ ｙｃ 和 ｃ ｒａｓ 表达降低,ｐ１６ 蛋白质表达降低．而同样浓度的 Ｃｅ Ｃｌ３ 对 Ｂ Ｇ Ｃ ８２３ 细胞和正常细胞 ２ Ｂ Ｓ未见影响．提示：稀土化合物抑制肺癌细胞 Ｐ Ｇ 的增殖以及降低其恶性度的作用机制可能与一些增殖相关的原癌基因的表达和细胞周期的调控有关,其确切的机理还需进一步的研究．     

Control of tubulin and actin gene expression in Tetrahymena pyriformis during the cell cycle

Poly(A)-containing mRNA was isolated from division synchronized populations of the ciliated protozoan, Tetrahymena pyriformis. The level of tubulin and actin mRNA at specific cell cycle stages was analyzed by hybridization to tubulin and actin cDNA probes and by gel analysis of their in vitro translation products. The pattern of fluctuation of tubulin mRNA levels was similar to that observed for the in vivo tubulin synthesis previously reported [1]. This suggests that as the cells progress through the cell cycle, tubulin synthesis is controlled at the mRNA level. There was little fluctuation of actin synthesis or actin mRNA levels during the cell cycle, which may be indicative of a different regulatory mechanism for actin than for tubulin.     

Synchronous division induced in Escherichia coli K12 by gemts mutants of phage Mu

Summary Infection with the bacteriophage mutant Mu c ⁺ gemts2 at 42° C induces synchrony in cell division in cultures of Escherichia coli K12. This synchrony may last for several cycles and is not only due to selection since synchronization is observed even when bacterial survival to the infection is over 80% as in lysogens for Mu c ⁺ gemts2. The mechanism by which sycnhrony is induced is not known, but since the product of Mu gene gem (previously called lig) has been shown to interact with the enzymatic system in the bacteria controlling the degree of DNA supercoiling, the phenomenon could be a consequence of this interaction.     

Microarrays and the relationship of mRNA variation to protein variation during the cell cycle

Microarray analyses have led to the postulated existence and identification of numerous genes that are believed to be expressed and presumably to act in a cell-cycle-specific manner because their expression varies during the cell cycle. It is important to see how protein variation can be produced from mRNA variation. We have calculated the protein content throughout the cell cycle resulting from cell-cycle-specific mRNA expression, and compared the result to protein content resulting from constant, cell-cycle independent, mRNA expression. For stable proteins, cell-cycle-specific mRNA expression leads to a maximum 2-fold change in protein content compared to proteins synthesized from constantly expressed mRNA. More realistic sinusoidal patterns of mRNA expression exhibit much smaller ratios of 1.25 or lower, even for extremely large amplitudes in mRNA expression. For unstable proteins that have a cycle-independent half-life, only at extremely short protein half-lives does mRNA variation have a significant impact on variation of protein content during the division cycle. We also apply these findings to proteins with a cycle-specific decay pattern. mRNA variations during the eukaryotic division cycle variation of mRNA during the cell cycle can have only a minimal affect on the variation of protein content during the cell cycle. We conclude that mRNA variations during the division cycle, as measured by microarrays, cannot by themselves, identify cycle-specific functions related to protein variations.     

人脑胶质瘤CDK4、CyclinD1和P16基因蛋白表达的免疫组织化学研究

采用检测人脑胶质瘤中CDK4、CyclinD1和P16基因蛋白的表达情况,探讨G1→S期细胞周期调节蛋白在胶质瘤发生,发展过程中的作用。对39例近期手术的胶质瘤标本和8例瘤旁正常脑组织标本进行免疫组织化学检测。结果显示：CDK4蛋白在良性、交界性胶质瘤和瘤旁正常脑组织中的表达差异没有显性意义（P＞0.05）,在恶性胶质瘤中的表达却有明显地增高,与前两比较差异均有显性意义（P＜0.05）。P16蛋白在恶性胶质瘤中的表达显低于在瘤旁正常脑组织和良性、交界性胶质瘤中的表达（P＜0.01）,但在后两中的表达差异没有显性意义（P＞0.05）。CyclinD1蛋白在三中的表达水平均较低且差异无显性意义（P＞0.05）。结果表明：CDK4蛋白的表达增高和P16蛋白的表达下调发生在胶质瘤的较晚期阶段,与胶质瘤的恶性变和恶性胶质瘤的发生有关,而CyclinD1蛋白的表达可能与胶质瘤的发生和发展无关。     

Differential expression of several E2-type ubiquitin carrier protein genes at different developmental stages inArabidopsis thaliana andNicotiana sylvestris

We characterized three genes encoding different E2-type ubiquitin carrier proteins involved in the ubiquitin-mediated proteolytic pathway:UbcAt3 shows homologies to the yeastCDC34 gene andUbcAt4a andUbcAt4b are two different genes homologous to theUbc1/4/5 subfamily in yeast. Their accumulation was analysed and compared with that of the different families encoding polyubiquitins, as well as the monoubiquitin fusion protein, which is considered as a marker for cell division, during various developmental stages including GO/S transition and senescence of higher plant cells. Our results imply that theseUbc genes are under the control of complex mechanisms, and are differentially regulated, but not necessarily co-regulated with ubiquitin genes. Even the closely relatedUbcAt4a andUbcAt4b genes of the same multigene subfamily are controlled by distinct regulatory mechanisms.     

Progress in understanding DNA replication control

Completion of genome duplication during the S-phase of the cell cycle is crucial for the maintenance of genomic integrity. In eukaryotes, chromosomal DNA replication is accomplished by the activity of multiple origins of DNA replication scattered across the genome. Origin specification, selection and activity as well as the availability of replication factors and the regulation of DNA replication licensing, have unique and common features among eukaryotes. Although the initial studies on the semiconservative nature of chromosome duplication were carried out in the mid 1950s in Vicia faba, since then plant DNA replication studies have been scarce. However, they have received an unprecedented drive in the last decade after the completion of sequencing the Arabidopsis thaliana genome, and more recently of other plant genomes. In particular, the past year has witnessed major advances with the use of genomic approaches to study chromosomal replication timing, DNA replication origins and licensing control mechanisms. In this minireview article we discuss these recent discoveries in plants in the context of what is known at the genomic level in other eukaryotes. These studies constitute the basis for addressing in the future key questions about replication origin specification and function that will be of relevance not only for plants but also for the rest of multicellular organisms.     

老龄动物卵母细胞表观遗传修饰的改变

卵母细胞退化是衰老造成母源性生育力下降的主要因素。退化的卵母细胞通常表现为细胞周期阻滞、减数分裂紊乱以及一些基因的表达异常,表观遗传修饰在此过程中亦发生了显著改变。本文介绍了卵子发生过程中的表观遗传修饰调控机理,综述了卵母细胞退化的表现,着重探讨了卵母细胞退化过程中表观遗传修饰的改变。     

细胞外基质对培养咽癌细胞增殖及p53、PCNA基因表达的影响

为探讨细胞外基质(ECM)对咽癌细胞生物学行为的影响,将两种咽癌细胞在ECM成分Ⅰ型胶原胶上进行细胞培养,通过免疫荧光染色及Western blot法对细胞增殖及p53、PCNA基因表达进行了研究。在Ⅰ型胶原上培养的细胞增殖活跃,并形成鳞状上皮样结构。PCNA表达量增加,p53表达阳性细胞主要分布于表层细胞,而基底层细胞表达少。结果说明ECM成分对咽癌细胞增殖及基因表达有调节作用。     

cyclin D1, cyclin E 在乳腺良、恶性病变中的表达及其与p16,p21waf1及Rb 蛋白的关系

为探讨cyclinD1,cyclinE在乳腺癌发生发展中的作用及其与细胞周期调控相关基因蛋白的关系,采用免疫组化检测17例非增生乳腺导管上皮、19例不同程度增生的导管上皮及59例乳腺癌中cyclinD1,cyclinE,p16,p21waf1及Rb基因蛋白的表达.结果显示1.非增生乳腺导管上皮除1例cyclinE过表达外均无cyclinD1和cyclinE的过表达.乳腺癌的cyclinD1和cyclinE的过表达率均明显高于良性乳腺组织(P<0.05).2.乳腺癌cyclinD1过表达与淋巴结转移呈正相关(P<0.05),瘤体直径大于5cm者cyclinE过表达呈增加趋势,但差异无显著性意义.3.CyclinD1和cyclinE的过表达呈正相关(P<0.05).4.从非增生乳腺导管上皮到增生直至乳腺癌,p16,p21与cyclinD1,cyclinE含量的比值逐渐递减,而p21含量高于cyclinD1的乳腺癌体积小、淋巴结转移率低(P<0.05).p21阳性率与cyclinD1过表达呈正相关(P<0.01),也随cyclinE的过表达呈上升趋势.Rb基因蛋白的强表达与cyclinD1过表达呈正相关(P<0.01).结果表明CyclinD1和cyclinE蛋白过表达频发于乳腺癌早期,它们可能与p16、p21waf1、pRb共同参与了乳腺癌的发生发展.