亚硫酸氢钠（SO2）对人血淋巴细胞染色体畸变,姊妹染色单体互换及微核的效应

本文研究结果表明,亚硫酸氢钠（二氧化硫）能够引起人血淋巴细胞姊妹染色单体互换（ＳＣＥ）和微核（ＭＮ）率的增加,可使淋巴细胞有丝分裂周期延迟及细胞分裂指数下降,且这些作用有显著的剂量效应关系。结果指出,亚硫酸氢钠在低浓度下仅引起细胞染色单体型畸变,在高浓度下既可引起染色单体型畸变,又可引起染色体型畸变。结果还指出,亚硫酸氢钠对染色体畸变（ＣＡ）和ＭＮ的诱发效应有明显的个体差异。硫酸钠未能引起上述细胞     

Sister Chromatid Cohesion

During S phase, not only does DNA have to be replicated, but also newly synthesized DNA molecules have to be connected with each other. This sister chromatid cohesion is essential for the biorientation of chromosomes on the mitotic or meiotic spindle, and is thus an essential prerequisite for chromosome segregation. Cohesion is mediated by cohesin complexes that are thought to embrace sister chromatids as large rings. Cohesin binds to DNA dynamically before DNA replication and is converted into a stably DNA-bound form during replication. This conversion requires acetylation of cohesin, which in vertebrates leads to recruitment of sororin. Sororin antagonizes Wapl, a protein that is able to release cohesin from DNA, presumably by opening the cohesin ring. Inhibition of Wapl by sororin therefore “locks” cohesin rings on DNA and allows them to maintain cohesion for long periods of time in mammalian oocytes, possibly for months or even years.DNA replication during the synthesis (S) phase generates identical DNA molecules, which, in their chromatinized form, are called sister chromatids. The pairs of sister chromatids remain united as part of one chromosome during the subsequent gap (G₂) phase and during early mitosis, in prophase, prometaphase, and metaphase. During these stages of mitosis chromosomes condense, in most eukaryotes the nuclear envelope breaks down, and in all species chromosomes are ultimately attached to both poles of the mitotic spindle. Only once this biorientation has been achieved for all chromosomes, the sister chromatids are separated from each other in anaphase and transported toward opposite spindle poles of the mother cell, enabling its subsequent division into two genetically identical daughter cells.This series of events critically depends on the fact that sister chromatids remain physically connected with each other from S phase until metaphase. This physical connection, called sister chromatid cohesion, opposes the pulling forces that are generated by microtubules that attach to kinetochores and thereby enables the biorientation of chromosomes on the mitotic spindle (Tanaka et al. 2000b). Without cohesion, sister chromatids could therefore not be segregated symmetrically between the forming daughter cells, resulting in aneuploidy. For the same reasons, cohesion is essential for chromosome segregation in meiosis I and meiosis II. Cohesion defects in human oocytes can lead to aneuploidy, which is thought to be the major cause of spontaneous abortion, because only a few types of aneuploidy are compatible with viability, such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) (Hunt and Hassold 2010). Studying the mechanisms of cohesion is therefore essential for understanding how the genome is passed properly from one cell generation to the next.In addition, sister chromatid cohesion facilitates the repair of DNA double-strand breaks in cells that have replicated their DNA, where such breaks can be repaired by a homologous recombination mechanism that uses the undamaged sister chromatid as a template (for review, see Watrin et al. 2006). Furthermore, mutations in the proteins that are required for sister chromatid cohesion can cause defects in chromatin structure and gene regulation, and can in rare cases lead to congenital developmental disorders, called Cornelia de Lange syndrome, Roberts/SC Phocomelia syndrome, and Warsaw Breakage syndrome (for review, see Mannini et al. 2010).     

Sister Chromatid Exchanges in Tradescantia Paludosa

A modified fluorescence-plus-Giemsa technique is described that allows differential staining of sister chromatids in root tip cells from cuttings of Tradescantia patudesa. With this staining technique, chromatids with both DNA strands unsubstituted are differentiated from chromatids containing 5-bromouracil in place of thymine in one of the strands of the DNA duplex. The baseline level of sister chromatid exchanges was shown to be dependent on the concentration of 5-bromodeoxyuridine in the treatment solution, the mean frequency being 43.5 sister chromatid exchanges per cell for the experimental protocol suggested.     

Chromosomal Aberrations (CA), Sister Chromatid Exchanges (SCE), and High-Frequency Cells (HFC) Frequencies in Peripheral Blood Lymphocytes of Tunisian Gasoline Truck Loaders

Gasoline constitutes a mixture of chemicals that contain well-known genotoxicants. Thus, chronic occupational exposure to gasoline may be considered to possess genotoxic risk. In this study, the frequencies of total chromosomal aberrations (TCA), aberrant cells (Ab.c.), sister chromatid exchanges (SCE), high-frequency cells (HFC), and high-frequency cell individual (HFI) were investigated in peripheral blood lymphocytes from 17 gasoline-exposed workers (10 smokers and 7 non-smokers) and 22 unexposed reference subjects (12 smokers and 10 non-smokers). The exposed subjects were gasoline truck loaders at a gasoline company from Tunis City, north of Tunisia. The results indicate multiple CA, such as dicentrics (DIC), chromatid breaks (SB), and chromosome breaks (DB). A significant difference was observed in TCA and Ab.c. frequencies between exposed and unexposed groups (p < 0.01). A significant difference was found in frequencies of SCE (p < 0.01) and HFI (p < 0.05) between exposed and unexposed groups. SCE and TCA frequencies of smokers were found to be significantly higher than those of non-smokers in both groups. There was an interaction between gasoline exposure and smoking habit for TCA (p = 0.020), but not for SCE. Our findings indicate that gasoline truck loaders were under risk of significant cytogenetic damage that was enhanced by their smoking habit.     

小麦愈伤组织细胞的姐妹染色单体交换

用BrdU标记,改良的FPG法染色,建立了一种植物愈伤组织细胞姐妹染色单体分染的方法。并对培养基的不同附加成分对SCE的影响进行了研究。所有培养基上愈伤组织细胞的SCE率都显著高于正常根尖分生组织细胞。6-BA,AgNO_3,高浓度的2,4-D,蔗糖均可诱发SCE。     

A Simplified Procedure for the Observation In Situ Of Chromosome Aberrations or Sister Chromatid Exchanges and the Estimation of the Mitotic Index in Mammalian Monolayer Cell Cultures

Chinese hamster V-79 cells are widely used in short term screening for potential physical or chemical mutagens of the environment. A simplified version of the standard Giemsa protocol of Moorhead and the Feulgen plus Giemsa protocol of Wolff and Perry is given which permits the observations in situ of chromosome aberrations or sister chromatid exchanges and the estimation of the mitotic index in the Petri dishes used for the culture of the V-79 cells.     

Chromatid recommensuration after segmental duplication

Background  

Midsegment duplication (dup) of chromatid arms may be symmetric or asymmetric. It can be argued that every dup should yield a discommensured RC with (a) loss of at least one duplicated unit to the template counterpart and; (b) deletion of all sections of the replicating chromatid arm that are distal to both the gap left by the duplicating process and the segment closest to the centromere.     

Statistical Analysis of Chromatid Interference

The nonrandom occurrence of crossovers along a single strand during meiosis can be caused by either chromatid interference, crossover interference or both. Although crossover interference has been consistently observed in almost all organisms since the time of the first linkage studies, chromatid interference has not been as thoroughly discussed in the literature, and the evidence provided for it is inconsistent. In this paper with virtually no restrictions on the nature of crossover interference, we describe the constraints that follow from the assumption of no chromatid interference for single spore data. These constraints are necessary consequences of the assumption of no chromatid interference, but their satisfaction is not sufficient to guarantee no chromatid interference. Models can be constructed in which chromatid interference clearly exists but is not detectable with single spore data. We then extend our analysis to cover tetrad data, which permits more powerful tests of no chromatid interference. We note that the traditional test of no chromatid interference based on tetrad data does not make full use of the information provided by the data, and we offer a statistical procedure for testing the no chromatid interference constraints that does make full use of the data. The procedure is then applied to data from several organisms. Although no strong evidence of chromatid interference is found, we do observe an excess of two-strand double recombinations, i.e., negative chromatid interference.