家猪染色体复制行为的研究

本文采用外周血培养、胸苷同步化细胞、Brdu连续标记和胸苷末端标记法研究了家猪染色体复制的过程。根据家猪染色体复制带型的不同,将复制过程分为5个不同的时期,提出了各个时期的判别标准,并绘制了复制过程模式图。在同步化的细胞群中研究了Brdu掺陶入时间和不同复制期出现频率的关系。发现了家猪端着红粒染色体和双臂染色体C带异染色质区的不同步复制现象。本文还对端着丝粒染色体微小短臂的结构、失活X色体复制起始位点多态性、常染色体中某些晚复制区的不同步复制现象进行了研究。     

西伯利亚狍成纤维细胞建系及其生物学特性分析北大核心CSCD

本研究以内蒙古大青山获得野生雄性和雌性西伯利亚狍(Capreolus pygargus)为实验材料,利用组织块贴壁培养法进行气管、肺和耳3种组织成纤维细胞原代建系,研究不同组织来源的细胞贴壁率、冷冻前及复苏后存活率、生长曲线,进一步绘制狍成纤维细胞核型图并分析其G带特征。实验结果显示,气管、肺和耳3种组织成纤维细胞增殖经历潜伏期、对数生长期、平台期三个阶段,细胞形态为梭形、三角形或不规则形,是典型成纤维细胞形态;成纤维细胞呈漩涡状生长,其中气管、耳成纤维细胞生长增殖能力最强、肺成纤维细胞增殖能力较弱,气管和耳组织来源成纤维细胞呈典型“S”型细胞生长特征。染色体核型及G带分析结果显示,雄性狍成纤维细胞染色体条数为2n=70,其中,有34对常染色体,形态类型为12条近端着丝粒染色体(st),22条亚中着丝粒染色体(sm),1对性染色体,X染色体为中着丝粒染色体(m),Y染色体为近端着丝粒染色体(st),5条超数染色体(B);雌性狍成纤维细胞染色体条数为2n=70,其中,有34对常染色体,其形态类型为29条亚中着丝粒染色体(sm),5条近端着丝粒染色体(st),1对为性染色体,X染色体为亚中着丝粒染色体(sm),8条超数染色体(B)。本研究成功建立了雄性和雌性西伯利亚狍气管、肺和耳3种组织来源的成纤维细胞系,在体外培养时生长状态良好且维持了细胞的遗传信息稳定性,绘制了西伯利亚狍雄性和雌性染色体核型及G带图谱,为将来更深入开展相关研究提供材料与基本技术支撑。     

14例闭经患者的细胞遗传研究

运用数种细胞遗传学技术研究了14例闭经患者的病因,发现11例(占78.6％)具有异常核型。包括45,Ⅹ(3例);45,Ⅹ/46,Ⅹ,i(Xq)(2例);45,Ⅹ/46,ⅩⅩ/47,ⅩⅩⅩ(1例);45,X/46,Ⅹ,idlc(X)(1例);16,X,idic(X)(1例);46,X,del(X)(q24)(1例);15,X/46,X,del(X)(p11.3)(1例)和46,XY(1例)。其中6例(54.5％)涉及X染色体结构异常。对闭经患者的细胞遗传病因、核型与表型之间的可能关系以及失活X染色体的迟复制区段进行了讨论。     

失活X染色体基因逃逸与系统性红斑狼疮的性别二态性

X染色体失活可平衡女性中两条X染色体的基因剂量。越来越多的证据表明,失活X染色体上存在许多能够逃逸失活的基因。逃逸的机制涉及到DNA、RNA、组蛋白的表观修饰以及众多的调控蛋白和染色质的空间结构。失活X染色体基因逃逸的研究为人类疾病(特别是自身免疫性疾病)性别二态性的研究开辟了新的途径。目前已证实包括TLR7、CD40L、IRAK-1、CXCR3、CXorf21等失活X染色体基因逃逸是系统性红斑狼疮(systemic lupus erythematosus,SLE)女性好发的重要原因。本文主要综述了失活X染色体上基因逃逸以及与SLE性别二态性形成的分子机制。阐明SLE性别二态性形成的分子机制,不仅对疾病的诊断、治疗具有重要意义,而且对深入揭示人类免疫系统的发育及调控机理也有重要的理论意义。     

X染色体失活机理研究

X染色体失活是哺乳动物中为实现雌性XX个体和雄性XY个体间X染色体上基因剂量补偿作用(dosage compensation)而普遍存在的一种现象,表现为雌性个体两条X染色体中的一条结构异固缩和大范围的基因失活。由于失活基因高度甲基化,曾经认为甲基化在这一过程中发挥重要作用并据此提出一些模型,但相反的证据不断积累使人们对甲基化在这一过程中的主导作用发生怀疑。由于X     

一例t(15q;Yq)的家系调查分析

本文报道一例遗传性t(15q;Yq)的家族遗传病。经外周血淋巴细胞培养,进行G-显带、C-显带、Q-荧光显带、Ag-NOR、X小体、Y小体等项检查,其染色体除先证者具有正常女性核型外,多余出Y长臂的荧光区部分,核型为46,XX,—15+t(15q;Yq)。家族中的5名主要成员中,3名男性均有一条与先证者相同的衍生染色体,核型为46,XY,—15+t(15q;Yq)为Y长臂部分二体型,其表型正常,并有生育能力。现将调查分析结果报道如下。     

X染色体的DNA序列结构不同于6、7、8、10、11、12号染色体

雌性哺乳动物X染色体上的大部分基因均因X染色体失活作用而失去表达能力 ,X染色体长臂表现失活更明显。虽然对X染色体失活的许多方面都有所了解 ,但是仍然不清楚失活信号沿着X染色体全长扩散的机制。为了了解X染色体是否有不同于其他染色体的基因组学特征 ,这些特征是否关系到X染色体的失活扩散和维持 ,分析 6、7、8、1 0、1 1、1 2号染色体和X染色体DNA序列 7碱基 (7nt)组合水平的结构是否显示差异。从NCBI基因库(http :∥www .ncbi.nlm .nih .gov genome guide)下载 7条染色体长臂各 6 0Mb区域。将这 6 0Mb区域分为 0 5Mb (或 5 0kb)一段 ,对每一段DNA做 7nt字符串组合分析 ,如 1～ 7,2～ 8,3～ 9…… ,记录每种 7nt字符串的频率 ,A、C、G和T4个硷基的 7nt字符串共有 4 7=1 6 384种组合。根据数字差异显示的结果 (http :∥www .ncbi.nlm .nih .gov genome guide) ,选择在扁桃腺生发中心B细胞中高表达的基因 70个 ,用以计算所有内含子 (有义链 )的 7nt频率值。每个内含子被记录为一组 7nt频率值 ,求和相同基因中的所有内含子相同 7nt字符串的频率值 ,再用该和乘以该基因的表达频率得该基因 7nt字符串的频率值 ,求和 70个基因的 7nt字符串的频率值称做intron 7nt,该值试图模拟细胞中RNA小片段的总和。     

一例t(1; 5）相互易位并伴inv(12)臂内倒位的报告

人类染色体平衡易位携带者多为表型正常，其 最显著的遗传效应是流产及生出染色体异常的子女。 我们在男性不孕症的研究中发现一例核型为46, X介 t(l; 5)(p12; q3l), inv(12) (q15 82405）的平衡易 位携带者并伴一条12号染色体臂内倒位。现报告如 下。     

一例罕见的X-常染色体平衡易位[46,X,t(Xq;15q]伴发自然流产

有关夫妇一方为平衡易位携带者所致流 产、死胎及先天性多发畸形的情况,近年来多见 报道,并日益引起妇产科医师和医学遗传工作 者的重视。绝大多数平衡易位发生在常染色体 与常染色体之间,极少发生在X染色体与常染 色体之间。由于X染色体对性发育的特殊影 响,所以这种少见类型的染色体易位更引人重 视。迄今为止,国内有关资料中尚未见X一常 染色体易位类型的报道。我们在为一对不明原 因自然流产的夫妇作外周血染色体检查中发现 女方的染色体核型为46, X, t (Xq+; 15q )o 现报道如下,并对某些平衡易位中的染色体部 分失活现象进行讨论。     

表皮生长因子对转化的小鼠成纤维细胞DNA拓扑异构酶活性的影响

我们用表皮生长因子对用氚标记的脱氧胸苷转化的C_3H_(10)T1/2 CL8细胞进行刺激,研究了表皮生长因子对该细胞胞浆及胞核内DNA拓扑异构酶活性的影响,结果发现,表皮生长因子可以使转化的小鼠成纤维细胞胞浆和胞核内的DNA拓扑异构酶活性增加。     

Analysis of DNA replication patterns of human fibroblast chromosomes the replication map

Summary A replication map of human fibroblast chromosomes from two diploid human female fibroblast lines, 46,XX and 46,X, del (X)(q13), was determined using the fluorescent plus Giemsa (FPG) technique. Each chromosome was found to stain homogeneously dark when thymidine was incorporated for the entire S phase of that particular cell. As the duration of exposure to thymidine progressively decreased by increasing the incubation time in bromodeoxyuridine, the staining intensity of chromosomes decreased and, concurrently, gaps in the staining began to appear. These gaps coincide with R bands and represent the earliest areas to complete DNA synthesis. As these areas widen and increase in frequency, first Q and G bands appear, and finally C bands.Homologous X chromosomes were easily differentiated by either a comparison of the bands present or their staining intensity. The replication kinetics of the structurally abnormal heterocyclic X chromosome were very similar to those of the normal heterocyclic X chromosome. The X chromosome with deletion of a portion of the long arm was consistently late in replication.     

DNA methylation of the X chromosomes of the human female: an in situ semi-quantitative analysis

We present an in situ semi-quantitative analysis of the global DNA methylation of the X chromosomes of the human female using antibodies raised against 5-methylcytosine. The antibodies were revealed by immunofluorescence. Images were recorded by a CCD camera and the difference in intensity of fluorescence between active (early replicating) and inactive (late-replicating) X chromosomes was measured. Global hypomethylation of the late-replicating X chromosomal DNA was observed in three cases of fibroblast primary cultures that were characterized by numerical and structural aberrations of the X chromosomes [46,X,ter rea(X;X), 48,XXXX and 46,X,t(X;15)]. In these cases, the difference between early and late-replicating X chromosomes was significantly greater than the intrametaphasic variations, measured for a pair of autosomes, that result from experimental procedures. In cells with normal karyotypes, the differneces between the two X chromosomes were in the range of experimental variation. These results demonstrated that late replication and facultative heterochromatinization of the inactive X are two processes that are not related to global hypermethylation of the DNA     

Evidence for a relationship between DNA methylation and DNA replication from studies of the 5-azacytidine-reactivated allocyclic X chromosome

We examined the sequence of DNA synthesis of the human active, inactive and reactivated X chromosomes in mouse-human hybrid cells. The two independent reactivants, induced by 5-azacytidine (5-azaC), expressed human hypoxanthinephosphoribosyl transferase (HPRT), and one also expressed human glucose-6-phosphate dehydrogenase (G6PD) and phosphoglycerate kinase (PGK). Restriction enzyme analysis of DNA methylation at the re-expressed loci revealed hypomethylation of CpG clusters, that characterizes the relevant genes on the active X. The transfer of active and inactive X chromosomes from the native environment of the human fibroblast to the foreign environment of the hybrid cell did not affect the specific replication sequence of either human X chromosome. The silent X chromosome when reactivated, remained allocyclic, and the first bands to replicate were the same as prior to reactivation. In one reactivant, however, further progression of replication was significantly altered with respect to the order in which bands were synthesized. This alteration in the replication of the silent X following 5-azaC-induced reactivation suggests that DNA methylation may modulate the replication kinetics of chromosomal DNA.     

Inactive normal X in a female leukaemic patient with an acquired X/autosome translocation

Summary An X;9;22 translocation was detected in bone marrow cells of a female patient with blastic crisis of CML. A dynamic study following 5-BrdU treatment showed that the inactive late-replicating X chromosome was the normal one. This pattern of X-chromosome replication appears to be superimposable on the most usual model found in congenital X/autosome translocations.It is suggested that preferential autosome translocation onto the active X chromosome could be the general rule in acquired X/autosome translocations associated with long survival.     

Tissue-specific heterogeneity in DNA replication patterns of human X chromosomes

Regional DNA replication kinetics in human X chromosomes have been analysed using BrdU-33258 Hoechst-Giemsa techniques in five cell types from human females: amniotic fluid cells, fetal and adult skin fibroblasts, and fetal and adult peripheral lymphocytes. In all cell types, the late-replicating X chromosome can be distinguished from its active, earlyreplicating homologue, and both the early and late X exhibit temporally and regionally characteristic internal sequences of DNA replication. The replication pattern of the early X in amniotic fluid cells and skin fibroblasts is similar to that of the early X in lymphocytes, although certain discrete regions are later-replicating in these monolayer tissue culture cells than are the corresponding regions in lymphocytes. However, DNA replication kinetics in late X chromosomes from amniotic fluid cells and skin fibroblasts are strikingly different from those observed in lymphocytes with respect both to the initiation and termination of DNA synthesis. The predominant late X pattern observed in 80–95% of lymphocytes, in which replication terminates in the long arm in bands Xq21 and Xq23, was never seen in amniotic fluid cells or skin fibroblasts. Instead, in these cell types, bands Xq25 and Xq27 are the last to complete DNA synthesis, while bands Xq21 and Xq23 are earlier-replicating; this pattern is similar to the alternative replication sequence observed in 5–20% of lymphocyte late X chromosomes. This replication sequence heterogeneity is consistent with the existence of tissue-specific influences on the control of DNA replication in human X chromosomes.     

Immunocytochemical evidence for methylation of the inactive X chromosome in human fetal oogonia

The state of DNA methylation of the X chromosomes of human interphase oogonia from a 46,XX and a 46,XX/47,XXX fetus at 17 weeks of gestation was tested immunocytochemically with an antibody to 5-methylcytosine (5MeC). Of 1637 oogonial nuclei from the 46,XX fetal ovary, 313 (19.1%) contained Barr bodies, of which 93.6% were positive for 5MeC. Of 1780 oogonia from the 46,XX/47,XXX fetus 327 (18.4%) contained Barr bodies; 175 oogonia had one Barr body and 152 had two. Of the single Barr bodies 145 (82.8%) had positive 5MeC reaction product. Of the 152 oogonia from the XXX line, 97 (63.8%) had positive 5MeC on both Barr bodies, 35 (23%) had one positive and one negative, and 20 (13.1%) had no product on either Barr body. This immunocytochemical evidence supports the hypothesis that the DNA of the inactive X-chromosome of the human 17-week gestation oogonium is methylated.     

Investigation of the “variable spreading” of X inactivation into a translocated autosome

Summary A new case of an unbalanced X/autosome translocation, karyotype 46,X,der(X),t(X;14)(q22;q11), is described. The derivative X chromosome was inactivated and showed various degrees of incomplete spreading of late replication into the translocated autosome. This enabled us to test the hypothesis that the extent of this spreading is primarily determined during X inactivation in the early embryo so that the various DNA replication patterns of the derivative X occur in a clonal fashion. However a dilution plating experiment gave no evidence that such a clonality exists. In the inactivated autosome, late-replicating bands obviously turned to earlier replication during cell aging in vitro. It is suggested that the degree of spreading of X inactivation into an autosome is not primarily induced but results from ineffective maintenance of the inactivation on the autosome, presumably due to an irreversible loss of methyl cytosine.     

FISH-detected delay in replication timing of mutated FMR1 alleles on both active and inactive X-chromosomes

X-chromosome inactivation and the size of the CGG repeat number are assumed to play a role in the clinical, physical, and behavioral phenotype of female carriers of a mutated FMR1 allele. In view of the tight relationship between replication timing and the expression of a given DNA sequence, we have examined the replication timing of FMR1 alleles on active and inactive X-chromosomes in cell samples (lymphocytes or amniocytes) of 25 females: 17 heterozygous for a mutated FMR1 allele with a trinucleotide repeat number varying from 58 to a few hundred, and eight homozygous for a wild-type allele. We have applied two-color fluorescence in situ hybridization (FISH) with FMR1 and X-chromosome α-satellite probes to interphase cells of the various genotypes: the α-satellite probe was used to distinguish between early replicating (active) and late replicating (inactive) X-chromosomes, and the FMR1 probe revealed the replication pattern of this locus. All samples, except one with a large trinucleotide expansion, showed an early replicating FMR1 allele on the active X-chromosome and a late replicating allele on the inactive X-chromosome. In samples of mutation carriers, both the early and the late alleles showed delayed replication compared with normal alleles, regardless of repeat size. We conclude therefore that: (1) the FMR1 locus is subjected to X-inactivation; (2) mutated FMR1 alleles, regardless of repeat size, replicate later than wild-type alleles on both the active and inactive X-chromosomes; and (3) the delaying effect of the trinucleotide expansion, even with a low repeat size, is superimposed on the delay in replication associated with X-inactivation. Electronic Publication     

X chromosomes attached by their long arm: replication autonomy of the short arm adjacent to the inactive centromere.

A 16 years old girl with Turner syndrome was found to have a 45,X/46,X,t(XqXq)?(q27q23) constitution. The two X chromosomes are attached by their long arms with loss of chromosome material and have one active and one inactive centromere. Analysis of replication patterns with autoradiography and BrdU treatment showed that the abnormal X is always the late replicating one and that the short arm of the second X which is adjacent to the inactive centromere maintains a degree of replication autonomy from the rest of the long arm.