端粒与端粒酶研究进展

细胞分裂中染色体因其末端（端粒）的DNA不能完全复制而短缩,使细胞逐渐失去增殖能力而衰老．端粒酶可延长染色体末端DNA,端粒酶的活化使细胞无限增殖．85％左右的恶性肿瘤端粒酶表达阳性,生殖细胞和无限繁殖的细胞系中端粒酶表达也呈阳性．文章综述了端粒的构成和功能、端粒酶在端粒合成中的作用,介绍了端粒酶活性的测定方法、细胞恶变与端粒酶激活的关系,并论及通过抑制端粒酶活性来治疗癌症的可能性．     

端粒生物学与肿瘤治疗

端粒的生物学功能主要是保护染色体末端,避免核酸酶对染色体末端的降解,防止染色体之间发生融合和重排。大多数人类肿瘤细胞通常通过端粒酶活性的重新激活来延长端粒,从而稳定染色体端粒DNA的长度。端粒酶是由端粒酶逆转录酶和端粒酶RNA模板组成的具有特殊逆转录活性的核糖核蛋白复合物。抑制端粒酶阳性细胞中的端粒酶活性会导致细胞凋亡或衰老。目前有多种以端粒和端粒酶为靶点来进行肿瘤治疗的策略。     

依赖端粒酶的端粒维持机制

端粒是真核生物染色体的末端重要结构复合物,对维持染色体稳定性起着重要作用。端粒酶的主要功能是复制端粒末端DNA,维持端粒长度。端粒酶活性调节与肿瘤发生和细胞衰老有着密切关系。本简要综述近年来依赖端粒酶的端粒维持机理的研究进展。     

端粒、端粒酶与肿瘤

端粒是真核细胞染色体末端含有 TTAGGG简单重复结构的复合体 ,它能防止染色体降解 ,端端融合 ,重组降解 ,因而有稳定染色体的作用。正常情况下 ,由于染色体复制的自身缺陷 ,细胞每分裂一次端粒要丢失 2 0～ 50 %碱基对 ,随着细胞分裂的增加 ,最终使细胞进入危机期 ,导致细胞死亡。端粒酶是一种 RNA、蛋白质的复合体 ,以 RNA为模板逆转录合成染色体末端的端粒 ,以维持染色体的稳定性。目前研究肿瘤组织细胞端粒酶活性高达 85～ 90 % ,而在正常组织细胞端粒酶活性较低。因此 ,端粒酶与肿瘤关系密切 ,端粒酶的研究成为国内外肿瘤的热点之…     

端粒酶(Telomerase)PCR ELISA——用于检测端粒酶活性的快速方法

宝灵曼公司最近推出了一种端粒酶PCR ELISA,它能对培养细胞或其他生物样品的细胞提取物中的端粒酶活性作高度灵敏的定性检测。 端粒是真核细胞染色体末端的特殊DNA-蛋白质结构,端粒DNA的特点是含有大量串连重复并富含G的重复序列,这些序列在进化中是高度保守的。端粒被认为可以阻止基因组DNA被降解或发生有害的重组,如:末端融合、重排、染色体易位和染色体缺失。由于     

哺乳动物早期胚胎端粒和端粒酶重编程

端粒位于真核染色体末端,是稳定染色体末端的重要元件。端粒酶(TER)是一种特殊的细胞核糖核蛋白(RNP)反转录酶(RT),其核心酶包括蛋白亚基和RNA元件。在DNA复制过程中的端粒丢失可以被有活性的端粒酶修复回来。哺乳动物端粒酶在发育中受调控,端粒的重编程可能是由于早期胚胎不同时期的端粒酶活性而造成的。因此,研究端粒和端粒酶重编程在早期胚胎发育中是非常重要的。该文综述了端粒和端粒酶的结构和功能,及其与哺乳动物早期胚胎发育的关系,并在此基础上展望了端粒和端粒酶在克隆动物胚胎发育的基础研究。     

端粒及端粒酶研究的最新进展

端粒是位于真核细胞染色体末端由重复DNA序列和蛋白组成的复合物,它具有保护染色体、介导染色体复制、引导减数分裂时的同源染爸体配对和调节细胞衰老等方面的作用。正常体细胞每分裂一代,端粒就会缩短一段,而端粒酶的作用是将一段端粒序列加到端粒末端,从而维持端粒长度。正常体细胞中是没有端粒酶活性的,而在大多数肿瘤细胞中都发现了端粒酶的表达,提示端粒和端粒酶在癌症发生和肿瘤细胞行为中具有重要作用。     

端粒、端粒酶在动脉粥样硬化中的研究进展CSCD

端粒是真核生物线性染色体末端的DNA重复序列,维持染色体的稳定性和DNA复制的完整性。DNA复制过程中,端粒逐渐缩短达到临界值时,染色体DNA被破坏而发生复制型衰老。端粒酶是催化端粒合成的酶,但在正常体细胞中活性很低。动脉粥样硬化是一种衰老相关性疾病,为冠心病、脑梗死、外周血管病发生发展的病理基础。新近研究发现,在动脉粥样硬化患者体内存在较短的端粒,并且较短的端粒更容易导致动脉粥样硬化。本文主要综述了参与动脉粥样硬化形成过程中细胞端粒长度和端粒酶活性的变化,以及这些变化对动脉粥样硬化形成的影响,并概括了动脉粥样硬化的危险因素与端粒和端粒酶的关系。     

HeLa细胞端粒酶最适反应条件及活性重建

端粒是真核细胞染色体末端的重复ＤＮＡ序列 ,其生物学功能是防止染色体ＤＮＡ降解、末端融合、非正常重组和染色体的缺失[1] .由于存在“末端复制问题” ,随着老化人体细胞端粒重复序列长度不断缩短 ,但在生殖细胞中由于端粒酶的存在 ,端粒序列并不缩短 .端粒酶是由蛋白质和ＲＮＡ构成的核蛋白 ,是依赖ＲＮＡ的ＤＮＡ聚合酶 ,在ＤＮＡ3’端合成端粒重复序列[2 ] .研究表明 ,在 85 %～ 95 %的人肿瘤细胞中可以检测到端粒酶的活性[3 ,4 ] ,而在正常体细胞中除生殖细胞和造血干细胞等极少数细胞中存在端粒酶活性外 ,均检测不到端粒酶活性 ,这…     

端粒、端粒酶在动脉粥样硬化中的研究进展

端粒是真核生物线性染色体末端的DNA重复序列,维持染色体的稳定性和DNA复制的完整性。DNA复制过程中,端粒逐渐缩短达到临界值时,染色体DNA被破坏而发生复制型衰老。端粒酶是催化端粒合成的酶,但在正常体细胞中活性很低。动脉粥样硬化是一种衰老相关性疾病,为冠心病、脑梗死、外周血管病发生发展的病理基础。新近研究发现,在动脉粥样硬化患者体内存在较短的端粒,并且较短的端粒更容易导致动脉粥样硬化。本文主要综述了参与动脉粥样硬化形成过程中细胞端粒长度和端粒酶活性的变化,以及这些变化对动脉粥样硬化形成的影响,并概括了动脉粥样硬化的危险因素与端粒和端粒酶的关系。     

Telomere regulation: lessons learnt from mice and men,potential opportunities in horses

Telomeres are genetically conserved nucleoprotein complexes located at the ends of chromosomes that preserve genomic stability. In large mammals, somatic cell telomeres shorten with age, owing to the end replication problem and lack of telomere-lengthening events (e.g. telomerase and ALT activity). Therefore, telomere length reflects cellular replicative reserve and mitotic potential. Environmental insults can accelerate telomere attrition in response to cell division and DNA damage. As such, telomere shortening is considered one of the major hallmarks of ageing. Much effort has been dedicated to understanding the environmental perturbations that accelerate telomere attrition and therapeutic strategies to preserve or extend telomeres. As telomere dynamics seem to reflect cumulative cellular stress, telomere length could serve as a biomarker of animal welfare. The assessment of telomere dynamics (i.e. rate of shortening) in conjunction with telomere-regulating genes and telomerase activity in racehorses could monitor long-term animal health, yet it could also provide some unique opportunities to address particular limitations with the use of other animal models in telomere research. Considering the ongoing efforts to optimise the health and welfare of equine athletes, the purpose of this review is to discuss the potential utility of assessing telomere length in Thoroughbred racehorses. A brief review of telomere biology in large and small mammals will be provided, followed by discussion on the biological implications of telomere length and environmental (e.g. lifestyle) factors that accelerate or attenuate telomere attrition. Finally, the utility of quantifying telomere dynamics in horses will be offered with directions for future research.     

Pharmacological intervention strategies for affecting telomerase activity: future prospects to treat cancer and degenerative disease

Telomerase enzyme is a ribonucleoprotein maintaining the length of the telomeres by adding G-rich repeats to the end of the eukaryotic chromosomes. Normal human somatic cells, cultured in vitro, have a strictly limited proliferative potential undergoing senescence after about 50-70 population doublings. In contrast, most of the tumor cells have unlimited replicative potential. Although the mechanisms of immortalization are not understood completely at a genetic level, the key role of the telomere/telomerase system in the process is clear. The DNA replication machinery is not able to replicate fully the DNA at the very end of the chromosomes; therefore, about 50-200 nucleotides are lost during each of the replication cycles resulting in a gradual decrease of telomere length. Critically short telomere induces senescence, subsequent crisis and cell death. In tumor cells, however, the telomerase enzyme prevents the formation of critically short telomeres, adding GGTTAG repeats to the 3' end of the chromosomes immortalizing the cells. Immortality is one of the hallmarks of cancer. Besides the catalytic activity dependent telomere maintenance, catalytic activity-independent effects of telomerase may also be involved in the regulation of cell cycle. The telomere/telomerase system offers two possibilities to intervene the proliferative activity of the cell: (1) inhibition the telomere maintenance by inhibiting the telomerase activity; (2) activating the residual telomerase enzyme or inducing telomerase expression. Whilst the former approach could abolish the limitless replicative potential of malignant cells, the activation of telomerase might be utilized for treating degenerative diseases. Here, we review the current status of telomerase therapeutics, summarizing the activities of those pharmacological agents which either inhibit or activate the enzyme. We also discuss the future opportunities and challenges of research on pharmacological intervention of telomerase activity.     

Ontogeny of telomerase in chicken: impact of downregulation on pre- and postnatal telomere length in vivo

Telomeres are the termini of linear chromosomes composed of tandem repeats of a conserved DNA sequence. Telomerase provides a mechanism for proliferating cells to offset telomeric sequence erosion by synthesizing new repeats onto the end of each parental DNA strand. Reduced or absent telomerase activity can lead to telomere shortening and genome instability. Telomeres and telomerase have not previously been characterized during ontogeny of any avian species. In the present study, telomerase activity in the chicken model was examined from early differentiation embryos through to adulthood. Telomerase activity was detected in all early embryos (preblastula through neurula) and in tissues throughout organogenesis. Subsequently, telomerase was downregulated in the majority of somatic tissues, either pre- or postnatally. A subset of tissues, such as intestine, immune and reproductive organs, exhibited constitutive activity. The impact of telomerase downregulation on telomere length was investigated and a telomere reduction of 3.2 kb in somatic tissues compared with germ line was observed in 5-year-old adults. The present results suggest that the telomere clock function is a conserved feature of avians as well as mammals. Knowledge regarding the relationships among telomerase regulation, proliferation/senescence profiles and differentiation status will be useful for numerous applications of chicken cells.     

Deletion of the major peroxiredoxin Tsa1 alters telomere length homeostasis

Reactive oxygen species (ROS) are proposed to play a major role in telomere length alterations during aging. The mechanisms by which ROS disrupt telomeres remain unclear. In Saccharomyces cerevisiae, telomere DNA consists of TG_(1–3) repeats, which are maintained primarily by telomerase. Telomere length maintenance can be modulated by the expression level of telomerase subunits and telomerase activity. Additionally, telomerase‐mediated telomere repeat addition is negatively modulated by the levels of telomere‐bound Rap1‐Rif1‐Rif2 protein complex. Using a yeast strain defective in the major peroxiredoxin Tsa1 that is involved in ROS neutralization, we have investigated the effect of defective ROS detoxification on telomere DNA, telomerase, telomere‐binding proteins, and telomere length. Surprisingly, the tsa1 mutant does not show significant increase in steady‐state levels of oxidative DNA lesions at telomeres. The tsa1 mutant displays abnormal telomere lengthening, and reduction in oxidative exposure alleviates this phenotype. The telomere lengthening in the tsa1 cells was abolished by disruption of Est2, subtelomeric DNA, Rap1 C‐terminus, or Rif2, but not by Rif1 deletion. Although telomerase expression and activity are not altered, telomere‐bound Est2 is increased, while telomere‐bound Rap1 is reduced in the tsa1 mutant. We propose that defective ROS scavenging can interfere with pathways that are critical in controlling telomere length homeostasis.     

Telomere and telomerase in oncology

Telomere and cell replicative senescenceTelomeres, which are located at the end of chro-mosome, are crucial to protect chromosome againstdegeneration, rearrangment and end to end fusion[1].Human telomeres are tandemly repeated units of thehexanucleotide TTAGGG. The estimated length oftelomeric DNA varies from 2 to 20 kilo base pairs,depending on factors such as tissue type and hu-man age. The buck of telomeric DNA is double-stranded, but the end of telomeric DNA consists of3' overhang of…     

Control of telomere length by a trimming mechanism that involves generation of t-circles

Telomere lengths are maintained in many cancer cells by the ribonucleoprotein enzyme telomerase but can be further elongated by increasing telomerase activity through the overexpression of telomerase components. We report here that increased telomerase activity results in increased telomere length that eventually reaches a plateau, accompanied by the generation of telomere length heterogeneity and the accumulation of extrachromosomal telomeric repeat DNA, principally in the form of telomeric circles (t-circles). Telomeric DNA was observed in promyelocytic leukemia bodies, but no intertelomeric copying or telomere exchange events were identified, and there was no increase in telomere dysfunction-induced foci. These data indicate that human cells possess a mechanism to negatively regulate telomere length by trimming telomeric DNA from the chromosome ends, most likely by t-loop resolution to form t-circles. Additionally, these results indicate that some phenotypic characteristics attributed to alternative lengthening of telomeres (ALT) result from increased mean telomere length, rather than from the ALT mechanism itself.