多囊卵巢病人淋巴细胞的rRNA基因活性

人类的rRNA基因位于5对近端着丝点染色体短臂的次缢痕上。间期细胞中,该区域转录45S rRNA并聚集形成核仁,因此把该区域称为核仁形成区(NOR)。在中期染色体制片上,核仁形成区常常靠近,这种现象叫做随体联合。一般认为随体联合是间期细胞核仁的残余。     

多囊卵巢病人淋巴细胞的rRNA基因活性

人类的rRNA基因位于,对近端着丝点染 色体短臂的次溢痕上。间期细胞中,该区域转 录45S rRNA并聚集形成核仁,因此把该区域 称为核仁形成区（NOR)。在中期染色体制片 上,核仁形成区常常靠近,这种现象叫做随体联 合。一般认为随体联合是间期细胞核仁的残余。     

正常人和21三体征家庭的银染核仁形成区的研究

DNA-RNA原位杂交术证明了人类18S—28S核糖体RNA基因位于5对近端着丝点染色体短臂的次缢痕处,即人类的核仁形成区(NOR)。1975年,Goodpasture和Howell等应用银氨法特异地染色核仁形成区,证实银染的位置是染色体上核糖体基因(rDNA)的位置。此后进一步证明银染物质不是rDNA,也不是rRNA,而可能是核仁     

正常人体细胞染色体银染核仁形成区的研究

原位分子杂交证明,各种哺乳动物的119 s- 28 S核搪体RNA基因（rDNA）位于特定的染色体的核仁形成区（NOR),最近,Gootlpasture 等应用银胺法特异地染色核仁形成区,证实银染的位置是染色体＿L核塘体RNA基因的位置。 此后,进一步证明银染物质不是rDNA,亦不是 rRNA,可能是核仁形成区特异的蛋白质,即和 r1:NA转录相联系的酸性蛋白。人类核糖体 RNA基因位于5对近端着丝点染色体短臂的 次猛痕处,即人类的核仁形成区。在正常人中, 常不是所有核仁形成区皆彼银染,其范围大约 4-10。应用银染法可以觉察正常人体核塘体 RNA基因的活动。     

遗传学实验

（十六）哺乳动物染色体的银染法实验原理 银染法（Ag-As技术）专染哺乳动物染色体上的核 仁组成区（nucleolar organizer region, NOR)。已知哺 乳动物中编码18S rRNA, 28S rRNA的基因（rDNA）是 位于特定染色体的核仁组成区。当用银染法染色时, rDNA能选择性地还原银,呈深黑色,染色深黑的可染 区即为核仁组成区（Ag-NORs )。可染区的数目反映了 有转录活性的核糖体RNA基因的数目。     

一种新的核仁组成区胶银染色技术

核仁组成区(Nucleolar OrganizerRegions,NORs)是位于细胞核仁内的DNA 环,具有 rRNA 基因,与 rRNA 的转录活性有关、在蛋白质合成中起重要的作用。遗传学家曾利用银染技术显示染色体核仁组成区来研究各种遗传缺陷性疾病。1986年 Ploton 建立丁一科改良的一步法胶银染色技术显示核仁组成区相关蛋白(Nucleoar Organizer Region Associa-ted Protein,AgNORs),虽然现在对这些蛋白染色的性质还不清楚,但该技术提供了一种快速检测核仁结构和活性改变的有效手段,已受到病理学界的高度重视,     

肝癌患者外周血淋巴细胞的rDNA活性及其四维时空遗传意义初探

人类D组和G组染色体的随体茎部为18S和28S rRNA基因(即rDNA)的座位,该区亦称为核仁形成区。应用细胞化学上的银染法可以判断rDNA的活性。至今已经证明,银染物质是同rRNA转录有密切联系的蛋白质,因而这是一个判别该区有何功能而不是有没有形态结构的简便有效方法。周宪庭等报道,在中国人中,随着年龄增长,该基因活性有丢失的趋势。银染法也很快用在肿瘤遗传学的研究中。H.Hubbell和徐道觉发现,一些肿瘤的细胞株,其每细胞的Ag-NORs(表示银染后出现阳性的rRNA基因数目)与正常对照组相     

核仁是怎样行使其生理功能的

真核细胞间期核中最显著的细胞结构是核仁。在光学显微镜下,核仁通常呈均质而致密的球体;在电子显微镜下,核仁主要分为三个区,即.1)颗粒区,含有核糖体前体颗粒;2)致密的丝状区即纤维区,包含有正在转录的RNA分子;3)浅染色区,或称为核仁内染色质,该区包含有从染色体核仁组织者区来的DNA,其中含有rRNA基因。因而,从成份上说,核仁是由DNA、RNA和蛋白质组成的,它的主要功能是转录rRNA和装配核糖体亚单位。     

玉米rRNA基因的组织和表达模式

玉米(Zea mays)只有1对45S rDNA位点并在分裂期染色体形成次缢痕, 是研究植物细胞rRNA基因组织和表达模式的简单模型。采用荧光原位杂交(fluorescence in situ hybridization, FISH)、CPD(PI与DAPI组合)染色和银染技术, 分析了玉米根尖分生细胞rRNA基因的组织和表达模式。45S rDNA探针在所有间期细胞核中显示2种杂交信号: 荧光强烈地位于核仁周边的纽, 而相对较弱地分布于核仁内的点。在部分细胞中可观察到点与纽相连或从纽发出; 点的数目越多, 纽变得越小; 点的数目多少与细胞的活性呈正相关。研究结果表明, 纽代表了处于凝缩状态的非活性的rDNA染色质, 纽解凝缩形成的点是rRNA基因活跃转录的细胞学表现; 不同阶段间期核的点的数目变化反映了被活化的rRNA基因数目不同。间期和前期细胞的CPD染色和相继的银染结果显示, 大部分rDNA染色质没有参与核仁的形成。rDNA FISH显示, 同一间期细胞的2个同源rDNA位点的表达水平存在差异, 同源染色体次缢痕的长度差异以及Ag-NOR和银染核仁的异态性进一步证实了这种差异的存在。FISH结果显示, 早中期细胞的rDNA染色质相对解凝缩, 银染在所有早中期细胞和部分中期细胞显示了明显的核仁, 表明玉米的rRNA基因在有丝分裂早中期有较活跃的转录, 其转录在晚中期才停止。     

正常615小鼠中期染色体核仁组织者银染观察

用银染方法(或称Ag-AS技术)对中期染色体的核仁组织者(NOR)进行特异性染色,能够显示18S和28S核糖体基因(rDNA)的活动。肿瘤细胞的rRNA具有较高速率的蛋白质合成能力。而被银染的酸性蛋白质在核仁的大小和组成上可能起重要作用。癌患者的核仁比正常成年人的核仁大。某些白血病患者的核仁有明显的变化。我们用改     

Segregation of acrocentric chromosome association in familial dicentric Robertsonian translocation t(14p;22p), aneuploidy (trisomy-21) and heteromorphism

The frequency and types of acrocentric chromosome association were quantitatively analysed in a Down syndrome child with unusual karyotype, 46, XX, -14, -22, t dic (14p;22p), +21, 21S+. Father and 4 sibs were heterozygous carriers for t dic (14p;22p). The variant 21S+ was inherited from the mother. The occurrence of translocation and trisomy in the same individual is extremely rare. Acrocentric chromosome association was analysed in this interesting family to understand the interrelationship of acrocentric chromosome association, Robertsonian translocation and heteromorphism, as possible predisposing factors for nondisjunction. Our findings suggest that acrocentric chromosome association is a heritable and nonrandom phenomenon. Heterozygous carriers for translocations and variants are likely to be at increased risk of nondisjunction. Long term family studies will enable to ascertain the causal-relationship of these factors more precisely.     

Karyotype of Saguinus labiatus labiatus (red-bellied marmosets)

The karyotype of Saguinus labiatus labiatus was determined by the Giemsa-banding technique on leukocytes cultured from 10 marmosets. The diploid chromosome number (2n = 46) was the same and the chromosome complement similar to other marmosets of genus Saguinus. Small karyotypic differences were found between S. l. labiatus and white-lipped marmosets (Saguinus fuscicollis) in the size of the X chromosome and in the banding pattern of one pair of metacentric chromosomes. A karyotypic variant was detected in 1 S. l. labiatus, characterized by a diploid chromosome number of 45 with balanced autosomal translocation involving two pairs of acrocentric chromosomes (T 16/19).     

Nucleolar organizer region variants as a risk factor for Down syndrome.

An unusual nucleolar organizer region (NOR) heteromorphism was noted among 13 of 41 parents in whom nondisjunction leading to trisomy 21 was known to have occurred. In contrast, only one of these double NOR (dNOR) variants was found among the 41 normal spouses and none were seen among 50 control individuals. In two dNOR(+) families, a second child with trisomy 21 was conceived. In both families, the extra chromosome in each child was contributed by the parent who carried the dNOR variant and resulted from a recurrent meiosis I error. Our data suggest that the dNOR heteromorphism may play a role in meiotic nondisjunction and could be associated with as much as a 20-fold increased risk for having offspring with trisomy 21.     

Understanding the mechanism(s) of mosaic trisomy 21 by using DNA polymorphism analysis.

In order to investigate the mechanism(s) underlying mosaicism for trisomy 21, we genotyped 17 families with mosaic trisomy 21 probands, using 28 PCR-detectable DNA polymorphic markers that map in the pericentromeric region and long arm of chromosome 21. The percentage of cells with trisomy 21 in the probands'' blood lymphocytes was 6%-94%. There were two classes of autoradiographic results: In class I, a "third allele" of lower intensity was detected in the proband''s DNA for at least two chromosome 21 markers. The interpretation of this result was that the proband had inherited three chromosomes 21 after meiotic nondisjunction (NDJ) (trisomy 21 zygote) and subsequently lost one because of mitotic (somatic) error, the lost chromosome 21 being that with the lowest-intensity polymorphic allele. The parental origin and the meiotic stage of NDJ could also be determined. In class II, a "third allele" was never detected. In these cases, the mosaicism probably occurred either by a postzygotic, mitotic error in a normal zygote that followed a normal meiosis (class IIA mechanism); by premeiotic, mitotic NDJ yielding an aneusomic zygote after meiosis, and subsequent mitotic loss (class IIB mechanism); or by a meiosis II error with lack of crossover in the preceding meiosis I, followed by mitotic loss after fertilization (class IIC mechanism). Among class II mechanisms, the most likely is mechanism IIA, while IIC is the least likely. There were 10 cases of class I and 7 cases of class II results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nucleolar organizer region heteromorphism associated with trisomy-21: a risk factor for non-disjunction?

An unusual nucleolar organizer region (double NOR) on chromosome 13 was observed in a Down syndrome child [47, XY, +21, dNOR(13)]. The variant chromosome was inherited from the mother [46, XX, dNOR(13)]. The extra chromosome 21 in the proband was maternal origin. The frequency of NOR chromosome association showed relatively high frequency in the mother and proband as compared to the controls. The result suggest that chromosome variants involving extra copies of NOR may indeed be involved in the meiotic nondisjunction of chromosome-21.     

Chromatid association in acrocentric chromosomes of abnormal sexual development (ASD) cases

Concordant/discordant associations at chromatid level were compared and found significant (P less than 0.05) in females with primary amenorrhea. This probably suggested that the acrocentric association pattern in this group of ASD and infertility did not follow a random segregation in subsequent cell divisions and that the concordant acrocentric chromosomes have regularly established physical connections with one another, held together for several cell cycles. It could only be speculated that the association of acrocentric chromosome anomalies in some females with abnormal sex chromosomes are due to this reason. In the event that chromosome association has a bearing on chromosome aberrations, the non-random pattern of acrocentric association probably would increase the choice for translocation and non disjunction in the somatic cells in females with primary amenorrhea during ontogenesis.     

Factors of maintaining chromosome polymorphism in common vole Microtus arvalis Pallas, 1779: reduced fertility and meiotic drive

The common vole Microtus arvalis (the form obscurus) exhibits polymorphism of a pericentric inversion in chromosome pair 5 throughout the species range. In the Urals populations, the frequency of an acrocentric variant of the heteromorphic chromosome is very low (on average 3.2%) and virtually does not change annually. The factors of maintaining stable chromosomal polymorphism in the common vole were studied under conditions of a laboratory colony. Heterozygous and homozygous for the acrocentric chromosome females showed a significant reduction of the reproductive output irrespective of the male karyotype. This effect was manifested mostly in litter size at birth. A number of cytogenetic and exophenotypic characteristics, as well as parent--offspring transmission of this chromosome in crosses of various types, were examined. We have found meiotic drive in favor of the acrocentric, as a result of which the frequency of the acrocentric (without taking into account the postnatal mortality) totaled over all cross variants (0.48) was significantly higher than that expected with random segregation (0.42). It is likely that meiotic drive of the acrocentric largely compensates for the reduced fertility of its carriers, being among the factors of maintaining it in natural populations.     

Factors of maintaining chromosome polymorphism in common vole Microtus arvalis pallas, 1779: Reduced fertility and meiotic drive

The common vole Microtus arvalis (the form obscurus) exhibits polymorphism of a pericentric inversion in chromosome pair 5 throughout the species range. In the Urals populations, the frequency of an acrocentric variant of the heteromorphic chromosome is very low (on average 3.2%) and virtually does not change annually. The factors of maintaining stable chromosomal polymorphism in the common vole were studied under conditions of a laboratory colony. Heterozygous and homozygous for the acrocentric chromosome females showed a significant reduction of the reproductive output irrespective of the male karyotype. This effect was manifested mostly in litter size at birth. A number of cytogenetic and exophenotypic characteristics, as well as parent-offspring transmission of this chromosome in crosses of various types, were examined. We have found meiotic drive in favor of the acrocentric, as a result of which the frequency of the acrocentric (without taking into account the postnatal mortality) totaled over all cross variants (0.48) was significantly higher than that expected with random segregation (0.42). It is likely that meiotic drive of the acrocentric largely compensates for the reduced fertility of its carriers, being among the factors of maintaining it in natural populations.     

A new chromosomal race (2n=44) of Nannospalax xanthodon from Turkey (Mammalia: Rodentia)

A new karyotype for blind mole rats was recorded in Tunceli province in Eastern Turkey. The karyotype contained 44 chromosomes, including 13 biarmed pairs, 7 acrocentric pairs, and one heteromorphic pair with a submetacentric and an acrocentric homologue in the autosomal complement (FNa=69). The X chromosome was submetacentric and the Y chromosome medium-sized subtelocentric (FN=73). Distinct dark centromeric C-bands were observed on most of the biarmed and three pairs of the acrocentric autosomes. The NORs were detected on short arms of three subtelocentric pairs and one acrocentric pair of autosomes. The diploid number of chromosomes and the karyotype characteristics observed are obviously unique among hitherto studied populations of blind mole rats and the complement can be evaluated as a new chromosome race of Nannospalax xanthodon. The distribution ranges of individual chromosome races of the species recorded in Eastern Anatolia are revised and possible interracial hybridization is discussed in respect of the finding of a new race.     

Prenatally detected marker chromosome identified as an i(22)(p10) using (micro)FISH

MicroFISH was used to elucidate the chromosomal origin of a prenatally detected marker chromosome. Five copies of the marker chromosome were collected from GTG-banded metaphases and amplified by means of DOP-PCR. The PCR product was labeled with blotine-14-dATP and used as a FISH probe for hybridization to metaphase chromosomes of the fetus (reverse painting). The marker appeared to be derived from the short arm of (an) acrocentric chromosome(s). After FISH with centromere-specific and band-specific probes complete characterization was possible and the marker chromosome appeared to consist of two short arms of chromosome 22. The pregnancy was continued and one year after birth the patient is developing normal.