UV-B辐射强对紫露草花粉母细胞的微核效应

臭氧层减薄引起紫外辐射的增强,紫露草三号用来监测辐射增加的潜在危害。在田间太阳光照下,把带有花序的紫露草枝条再给予8h不同UV-B剂量的照射,及用8μW／cm2的UV-B分别照射2、4、6和8h四种不同处理。处理后镜检花粉母细胞的微核发生情况。结果表明,UV-B照射处理花粉母细胞后其微核率显著增加。紫露草花粉母细胞的微核率可用作监测环境UV-B辐射增强的可靠指标。     

Increased micronucleus,nucleoplasmic bridge,nuclear bud frequency and oxidative DNA damage associated with prolactin levels and pituitary adenoma diameters in patients with prolactinoma

Prolactinoma is the most common pituitary tumor. Most pituitary tumors are benign, but they often are clinically signi?cant. We investigated cytokinesis-block micronucleus cytome (CBMN cyt) assay parameters and oxidative DNA damage in patients with prolactinoma to assess the relations among age, prolactin level, pituitary adenoma diameter and 8-hydroxy-2’-deoxyguanosine (8-OHdG) level in patients with prolactinoma. We investigated 27 patients diagnosed with prolactinoma and 20 age- and sex-matched healthy controls. We measured CBMN cyt parameters and plasma 8-OHdG levels in peripheral blood lymphocytes of patients with prolactinoma and controls. The frequencies of micronucleus (MN), nucleoplasmic bridge, nuclear bud, apoptotic and necrotic cells, and plasma 8-OHdG levels in patients with prolactinoma were significantly greater than controls. MN frequency was correlated positively with age, prolactin levels and pituitary adenoma diameters in patients with prolactinoma. The increased chromosomal and oxidative DNA damage, and the positive correlation between MN frequency, prolactin levels and pituitary adenoma diameters may be associated with increased risk of cancer in patients with prolactinoma, because increased MN frequency is a predictor of cancer risk.     

上海四膜虫S1的克隆老化

上海四膜虫Ｓ１经过３年传代培养后,多数细胞失去小核,一些细胞的细胞质中出现大核排了出的染色质和核仁的团块,克隆消除,ＯＨ自由基的能力也明显下降,在２５℃下传代的克隆消除ＯＨ自由基能力低于在液氮中保存的克隆,失去小核的细胞消除,ＯＨ自由基能力低于有小核细胞,这些变化说明上海四膜虫克隆在生理上已经进入老化的阶段,但是老化的克隆仍能靠分裂繁殖而长期不死,我们设想,上海四膜虫小核消失量一个复杂的过程,在主     

Genomic exclusion in Tetrahymena thermophila: A cytogenetic and cytofluorimetric study

Genomic exclusion is an aberrant form of conjugation of Tetrahymena thermophila in which the genome of a defective conjugant is excluded from the genotype of the exconjugant progeny. This paper is concerned with the cytogenetic and nucleocytoplasmic events of genomic exclusion in senescent clones A*III and C*. In crosses between A*III or C* and strain B, functional, haploid gametic nuclei are formed only in the strain B cell. In some instances one of the gametic nuclei divides prior to transfer of the migratory gametic nucleus, and both products then undergo DNA synthesis. Two alternative cytogenetic pathways are followed after transfer of the migratory nucleus. In the first, the conjugants separate without further micronuclear divisions. This pathway was most common in A*III genomic exclusion. In exconjugants the former gametic nuclei undergo both DNA synthesis and (presumably) intranuclear separation of centromeres to restore micronuclear diploidy. The old macronucleus of each exconjugant is retained without autolysis. This class of exconjugant survives and contributes genes to future sexual progeny. In the second cytogenetic pathway the gametic nuclei divide and macronuclear anlagen are formed, as in normal conjugation. This pathway was more common in C* genomic exclusion. The initial DNA content of the anlagen ranges from haploid to diploid. Following two to three rounds of DNA synthesis, further macronuclear development ceases and the anlagen appear to undergo autolysis. The old macronucleus condenses and also undergoes autolysis, as in normal conjugation. Except for rare C* exconjugants, in which macronuclear development is completed, anlagen-bearing genomic exclusion exconjugants die. Death may be caused by aneuploidy, errors in the timing or receptivity to signals for autolysis, or the inability of anlagen-bearing exconjugants to feed. Anlagenbearing conjugants are frequently abnormal with respect to the number of anlagen and micronuclei. Most of the anomalies can be explained by postulating errors in the timing of both developmental signals and nuclear divisions. Rare conjugants in which gametic nuclei divide but do not give rise to macronuclear anlagen are also observed. In these instances, the old macronuclei condense and undergo autolysis. Destruction of the old macronucleus therefore is independent of the presence of macronuclear anlagen and requires cell pairing in order to be initiated.     

The present status of higher plant bioassays for the detection of environmental mutagens

Higher plants provide valuable genetic assay systems for screening and monitoring environmental pollutants. They are now recognized as excellent indicators of cytogenetic and mutagenic effects of environmental chemicals and are applicable for the detection of environmental mutagens both indoor and outdoor. Comparisons between plant and nonplant genetic assay systems indicate that higher plant genetic assays have a high sensitivity (i.e. few false negatives). Two assays which are considered ideal for in situ monitoring and testing of airborne and aqueous mutagenic agents are the Tradescantia stamen hair assay for mutations and the Tradescantia micronucleus assay for chromosome aberrations. Both assays can be used for in vivo and in vitro testing. Other higher plant gentoxicity assys which have a large number of genetic markers and/or data base and are also highly suitable for testing for genotoxic agents include Arabidopsis thaliana, Allium cepa, Hordeum vulgare, Vicia faba, and Zea mays. Since higher plant systems are now recognized as excellent indicators of the cytotoxic, cytogenetic, and mutagenic effects of environmental chemicals and have unique advantages for in situ monitoring and screening it is recommended that higher plant systems be accepted by regulatory authorities as an alternative first-tier assay system for the detection of possible genetic damage resulting from pollution or the use of environmental chemicals. The results from higher platn genetic assays could meke a significant contribution in protecting the public from agents that can cause mutation and cancer. The advantages possessed by higher plant genetic assays, which are inexpensive and easy to handle, make them ideal for use by scientists in developing countries.     

The somatic function of the micronucleus in asexual reproduction of Paramecium: thermosensitivity of amicronucleates

It has been established that following removal of the micronucleus in Paramecium tetraurelia, the amicronucleate cell line enters a depression period, characterized by slow growth rate and oral abnormalities, at normal growth temperature (27°C). Such cell lines gradually recover in growth rate and stomatogenesis. In the present study, 4 recovered amicronucleate cell lines were challenged with high temperatures (35°C, 36°C, and 36.5°C). They exhibited growth rate reduction and abortive cytokinesis at 35°C and 36°C, and died at 36.5°C. In addition, they demonstrated oral defects similar to those observed in the depression period: disruption of the regular oral membranellar pattern, reduction in the length of the oral apparatus, and impaired phagocytosis (food vacuole formation). These high temperature-induced abnormalities were largely restricted to amicronucleates, and were rare or seen to a much lesser extent in sister micronucleate cell lines. This study demonstrates the participation of the micronucleus in conferring thermotolerance on the cells. It is hypothesized that the micronucleus specifies heat-shock proteins to maintain the integrity of oral and somatic cytoskeletal elements at high temperature.     

培养人淋巴细胞分裂阻滞与常规微核测试法的比较研究 Ⅱ.丝裂霉素C的遗传毒性效应

为了确定胞质分裂阻滞微核测试法(CB-MNT)的实用价值,本研究用0.025-0.4μg/mL的丝裂霉素C(MMC)处理培养的人体外周血淋巴细胞,比较CB-与常规(C)-MNT检测遗传毒性的敏感性,结果表明:(1)在整个剂量范围内,两法测得的微核率(MNF)均有良好的剂量效应关系,但CB法测得MNF低于常规法,随剂量增加而加著;CB法测知的最低浓度为0.1μg/ml,常规法为0.025μg/ml,可见常规法的敏感性优于CB法;(2)我们首次比较了CB法与常规法所检测微核的平均体积,发现CB法检测微核的体积接近常规法的3倍,并提出由于微核形成前后,微核间及微核与主核间的融合,导致了微核体积的增大和数量的减少,进而引起了MNF的下降;(3)CB法检测健康人自发MNF明显高于常规法,这可能是CB法检测低剂量诱变剂效应,较常规法不够敏感的重要原因之一。最后作者结合文献讨论了CB-与C-MNT的实用价值。     

Diversification of HP1‐like Chromo Domain Proteins in Tetrahymena thermophila

Proteins that possess a chromo domain are well‐known for their roles in heterochromatin assembly and maintenance. The Heterochromatin Protein 1 (HP1) family, with a chromo domain and carboxy‐terminal chromo shadow domain, targets heterochromatin through interaction with histone H3 methylated on lysine 9 (H3K9me2/3). The structural and functional diversity of these proteins observed in both fission yeast and metazoans correlate with chromatin specialization. To expand these studies, we examined chromo domain proteins in the ciliate Tetrahymena thermophila, which has functionally diverse and developmentally regulated heterochromatin domains. We identified thirteen proteins similar to HP1. Together they possess only a fraction of the possible chromo domain subtypes and most lack a recognizable chromo shadow domain. Using fluorescence microscopy to track chromatin localization of tagged proteins through the life cycle, we show evidence that in T. thermophila this family has diversified with biological roles in RNAi‐directed DNA elimination, germline genome structure, and somatic heterochromatin. Those proteins with H3K27me3 binding sequence characteristics localize to chromatin in mature nuclei, whereas those with H3K9me2/3 binding characteristics localize to developing nuclei undergoing DNA elimination. Findings point to an expanded and diversified family of chromo domain proteins that parallels heterochromatin diversity in ciliates.     

Macro- and Micronuclei of Tetrahymena pyriformis: A Model System for Studying the Structure and Function of Eukaryotic Nuclei*†

The macro- and micronucleus of Tetrahymena pyriformis are formed from a common diploid synkaryon during conjugation. Shortly after the 2nd postzygotic division, distinct morphologic and physiologic differences develop between the 2 nuclei. Micronuclei remain small, presumably diploid, and electronmicroscopic observations indicate that micronuclear DNA is contained in a dense, fibrous, chromosome-like coil. Macronuclei contain considerably more DNA than micronuclei, and the DNA of the macronucleus is found largely in the chromatin bodies typical of ciliate nuclei. The functional differences between macro- and micronuclei in vegetative cells also are striking. The template activity of DNA in the micronucleus is highly restricted compared to that in the macronucleus. Micronuclei synthesize and contain little RNA, and do not contain either nucleoli or ribonucleoprotein granules. Macronuclei, on the other hand, synthesize and contain large amounts of RNA and have many nucleoli and ribonucleoprotein granules. Macro- and micronuclei also have distinct differences in the timing of DNA synthesis during the cell cycle and in the timing and mechanism of nuclear division. Finally, during conjugation the macronucleus becomes pycnotic and disappears while the micronucleus undergoes meiosis and fertilization, ultimately giving rise to new macro- and new micronuclei. In short, the macro- and micronuclei of Tetrahymena provide an excellent system for studying the molecular mechanisms by which the same (or related) genetic information is maintained in different structural and functional states. Methods have been devised to isolate and purify macro- and micronuclei of Tetrahymena in the hope of correlating differences in the nucleoprotein composition of these nuclei with differences in their structure and function. The DNAs of macro- and micronuclei have been found to differ markedly in their content of a methylated base, N⁶-methyl adenine, and major differences in the histones of the 2 nuclei have been observed. Macronuclei contain histones similar to those found in vertebrate nuclei, while 2 major histone fractions seem to be missing in micronuclei. In addition, histone fraction F2A1 which is found in multiple, acetylated forms in macronuclei, is present only as a single, unacetylated form in micronuclei.     

Efficient induction by amiprophos-methyl and flow-cytometric sorting of micronuclei in Nicotiana plumbaginifolia

Amiprophos-methyl (APM) is a potential herbicide which acts at the level of microtubules. By exposure of suspension cells of Nicotiana plumbaginifolia to this agent, a high degree of metaphase arrest was observed and single as well as groups of chromosomes were scattered throughout the cell, offering good prospects for application in cytology and chromosome isolation. After prolonged exposure to the drug, the chromosomes decondensed and micronuclei were formed. Based on their DNA content, the micronuclei were sorted by flow cytometry. Prospects for application of isolated micronuclei for partial genome transfer and gene mapping are discussed.Abbreviation APM amiprophos-methyl