NORs and statellite associations in a family with 13/14 translocation

Summary The distribution and size of Ag-NORs and the frequency of satellite associations was investigated in a family where the mother and a son were 13/14 translocation carriers. In cells with good quality silver impregnation and G-banding, Ag-NORs were constant per subject in number and distribution, while Ag-NOR size varied from cell to cell. The father had the maximal number Ag-NORs (10). The mother's translocation chromosome, free chromosome 13 and both chromosomes 22 were Ag-NOR negative and these were transmitted to the children. The mean number of associations per cell for a particular subject was positively correlated with the subject's characteristic number of Ag-NORs. In this family, the positive correlation was also present between mean Ag-NOR sizes of acrocentric homologue chromosome pairs and their coefficient of association. No biological mechanism compensating for the absence of active NORs was demonstrated for this family.     

Deoxycytidine reverses the suppression of nucleolar organizer regions' activity caused by BrdU

Summary In this article we report that 5-bromodeoxyuridine (BrdU) significantly suppresses the nucleolar organizer regions (NORs) activity of Chinese hamster cells (both dipliod cells and cell line Wg3-h) (P<0.001). One of the most obvious characteristics of the suppression is a significant decrease in the total number of the Ag-NORs per cell rather than in a frequency variation of the associated Ag-NORs. The decrease in the Ag-NORs number is mainly because of the decrease in number of chromosomes bearing 2 Ag-NORs. The degree of the suppression increases with increase in BrdU concentration in the culture medium. There is a close relationship between the suppression and the BrdU-treatment time, i.e. for a given concentration of the BrdU, the longer the BrdU-treatment time, the stronger the suppression. When the BrdU-treated cells are transferred into BrdU-free medium and allowed to grow in it for another 30 h, NORs activity can be restored. Therefore, the suppression of NORs activity may be due to BrdU toxicity. When deoxycytidine (dC) is added into medium containing 30 g/ml of BrdU, the total number of both the Ag-NORs and the chromosomes bearing Ag-NORs per cell increases to the level of untreated cells. Our results thus indicate that the addition of dC reverses the suppression of the NORs activity caused by BrdU.     

Chromosome banding in salmonid fish: nucleolar organizer regions in Salmo and Salvelinus

Chromosome banding patterns obtained by silver staining (Ag-NORs) were analyzed in three species of Salmo (rainbow, brown trout, and Atlantic salmon) and three species of Salvelinus (brook trout, lake trout, and arctic char). In rainbow trout and Atlantic salmon the Ag-NORs were found at the secondary constrictions of a single chromosome pair, while in brown trout the Ag-NORs were found on the short arms of one or two of the two longest subtelocentric or acrocentric chromosome pairs. The location of the Ag-NORs was multichromosomal in the three Salvelinus species, occurring on one or both members of four to six different chromosome pairs in different individuals. The Ag-NOR sites were on the short arms of some acrocentric pairs and at the telomeres of other acrocentric pairs and one or two metacentric pairs. Chromomycin A3 positive bands were found at the same sites as the Ag-NORs in all species. In the species with multichromosomal location of Ag-NORs, polymorphisms in the size and location of the NORs were extremely common, so that almost every individual fish had a different pattern of Ag-NOR sites.     

Visualization of nucleolar organizer regions in mammalian chromosomes using silver staining

A simple ammoniacal silver staining procedure, designated Ag-AS, differentially stains the chromosomal locations of ribosomal DNA in certain mammalian species. This was critically demonstrated by Ag-AS staining of the nucleolus organizer regions in karyotypes of the same species and cell lines used for locating the ribosomal cistrons by DNA/RNA in situ hybridization. With Ag-AS, silver stained NORs (Ag-NORs) are visualized as black spherical bodies on yellow-brown chromosome arms. Ag-NORs were visualized throughout mitosis at the secondary constrictions in the rat kangaroo, Seba's fruit bat, Indian muntjac, and Rhesus monkey. The Chinese hamster and cattle have telomeric Ag-NORs, the mouse subcentromeric Ag-NORs, and the field vole Ag-NORs as minute short arms or choromosomal satellites. Ag-NORs occur at both secondary constrictions and at telomeres in the cotton rat. Variability in Ag-NOR pattern included differences in the number of Ag-NORs per cell within a cell population, size of Ag-NORs among chromosomes of a complement, and presence of Ag-NOR on particular chromosomes in two cell lines of the Chinese hamster. The available cytochemical data suggest that the Ag-AS reaction stains chromosomal proteins at the NOR rather than the rDNA itself.     

Nucleolar organizing regions of human chromosomes

Summary Silver-Stained cells from 49 parents with a history of several abortions were compared with cells from 35 parents with normal liveborn children. The modal and mean number of silver-stained NORs (Ag-NORs) observed on D- or G-group chromosomes was similar in both groups and between males and females. Ag-NORs were randomly distributed on all five acrocentric pairs. The distribution and size of Ag-NORs within an individual was not random and was fairly consistent from cell to cell.The mean number of associations per cell was similar in both males and females of the abortion group and was less than the number of associations in controls. The probability of D- or G-group chromosomes being associated was near the expected probability of 0.6 for D-association and 0.4 for G-association. The frequency of association of any chromosome combination did not differ statistically from the expected values, though the number of associations, 15/22, was higher than expected.     

Localization of rRNA genes in Phyllostomidae bats reveals silent NORs in Artibeus cinereus

We analyzed the nucleolus organizer regions (NORs) of thirteen bats from genera Phyllostomus, Phylloderma, Trachops, Tonatia, Sturnira, Platyrrhinus, Artibeus and Glossophaga. We used silver staining and FISH with rDNA probe. Nine species had only one Ag-NOR-bearing chromosome pair. Artibeus lituratus, A. jamaicensis and A. fimbriatus presented multiple Ag-NORs located in the short arms of pairs 5, 6 and 7, and an additional mark in the long arm of one chromosome 5 in A. fimbriatus. Artibeus cinereus showed Ag-NORs in the chromosome pairs 10 and 13. The chromosomal location of rRNA genes using FISH agreed with the number and position of NORs in all but one species. In A. cinereus the hybridization signals were seen in three chromosome pairs 9, 10 and 13. This suggests the occurrence of silent NORs in pair 9. Differences in the size and intensity of the hybridization signals were also observed in the pair 9 of A. cinereus.     

A Population Analysis of the Structure and Variability of NOR in Salmo Trutta by Ag, CMA3 and ISH

An analysis of the variation in the number and location of rDNA genes has been carried out in two populations of brown trout (Salmo trutta) from Poland by using Ag and CMA₃-staining, and rDNA in situ hybridisation. We observed an interindividual variation in arm number with NF = 100, 101, and 102. This variation was connected with the size polymorphism of the short (NOR-bearing) arm of the chromosome pair 11. The population studied showed a multichromosomal distribution of active NORs. Atypical Ag-NORs consisted of rDNA genes, as evidenced by rDNA-ISH. In addition to individuals with standard NORs, specimens with extra NORs as well as others with only one active NOR and single interphase nucleolus were observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Differential rRNA genes expression in bread wheat and its inheritance

The expression of the ribosomal RNA (rRNA) genes from rye, located within the nucleolus organizer regions (NORs), is repressed by cytosine methylation in wheat x rye hybrids and in triticale, as consequence of nucleolar dominance. Our previous study revealed that bread wheat cultivars with a maximum number of four Ag-NORs presented high level of rDNA cytosine methylation when compared to others with a maximum of six Ag-NORs. In order to evaluate the inheritance of the Ag-NORs number and NOR methylation patterns, we produced F₁ hybrids between bread wheat cultivars with four Ag-NORs and bread wheat cultivars with six Ag-NORs (in the direct and reciprocal senses). The F₂ progenies of these F₁ hybrids were also evaluated for the NOR number and methylation patterns. Parent bread wheat cultivars with a maximum of four Ag-NORs after treated with 5-azacytidine evidenced a maximum of six Ag-NORs per metaphase cell and a maximum of six nucleoli per interphase nucleus, confirming that the expression of the rRNA genes in bread wheat is related to cytosine methylation. Most of the F₁ hybrids showed a maximum number of four or six Ag-NORs, similarly to that of the female parent suggesting a non-mendelian inheritance, while other hybrids presented four or six Ag-NORs in both senses of the cross. The F₁ NOR methylation patterns showed some fragments common to their parents but also novel fragments suggesting genomic and/or chromosome rearrangements after hybridization. Despite the different NOR patterns among the parents, an invariable NOR pattern was found among the F₁ plants suggesting a tendency to stability, which was also transmitted to the F₂. The F₂ progenies showed plants with a maximum of four, five and/or six Ag-NORs. The ratio of plants with four, five and/or six Ag-NORs per F₂ progeny was variable and did not follow any specific mendelian proportion. These results allowed us to suggest that the inheritance of the number of Ag-NORs by the F₁ and F₂ plants did not follow any mendelian inheritance and were not correlated to NOR methylation patterns in contrast to what was verified for their parents.     

Cytological research on the argentophilic nucleolus-organizer regions of the metaphase chromosomes in parthenogenetic mouse embryos]

Silver staining technique visualizing argentophilic nucleolus organizer regions (Ag-NORs) was used for studying parthenogenetic mouse embryos produced by artificial activation of oocytes in Ca(2+)-Mg(2+)-free medium. Ag-NOR-containing chromosomes were detected in metaphases of parthenogenetic embryos during six successive cleavage divisions starting with the two-cell stage. The frequency of metaphases with varying AG-NOR number in diploid parthenogenones was similar to that in the control (fertilized) embryos. Average number of metaphase Ag-NOR chromosomes (calculated per diploid chromosome set) in haploid parthenogenones exceeded that in the control; in some cases all NORs were stained by silver. This is evidence that latent ribosomal cistrons in some chromosomes can be activated.     

经甫树蛙的染色体组型、C带和Ag-NORs的研究

本文分别用骨髓细胞染色体标本制作法、BSG技术和一种快速、简便的Ag-NORs显带技术,首次研究了经甫树蛙的染色体组型、C带和Ag-NORs。结果表明,经甫树蛙2n=26,有5对大型和8对小型染色体,次缢痕在No.11染色体长臂末端,为C带负染;银染表明,此次缢痕处即是经甫树蛙的“标准NORs”经甫树娃的C带结构异染色质主要是着丝点型和插入型的。文章初步讨论了树蛙属的细胞分类、经甫树蛙次缢痕、Ag-NORs和C带的关系。     

Analysis of nucleolus organizer regions (NORs) in mitotic and polytene chromosomes ofPhaseolus coccineus by silver staining and Giemsa C-banding

Chromosomes with active nucleolus organizer regions (NORs) were visualized in root tip metaphases ofPhaseolus coccineus using the silver staining technique. A mean number of 5.5 Ag-NORs per cell was observed in 54 cells from eight plants. In the endopolyploid nuclei of the suspensor the silver technique did not demonstrate the reported specificity for nucleolus organizer activity, because there was usually pale staining of nucleoli and preferential staining of heterochromatic regions in the polytene chromosomes including pericentromeric material, telomeres and NORs. The mean number of NORs per nucleolus as detected by this method was 5.8 (28 nucleoli analysed). Using a modified preparation technique, giant chromosomes stained pale, but nucleoli of suspensor cells displayed darkly silver staining internal domains, each of which originating from a nucleolus organizer.—Giemsa C-banding of endopolyploid suspensor nuclei revealed C-positive nucleolus organizers with darkly staining intranucleolar fibrils. The latter were frequently involved in inter-NOR associations. In 34 nucleoli analysed, the mean number of Giemsa C-positive NORs per nucleolus was 6.0.Dedicated to Professor Dr.Lothar Geitler on the occasion of his 80th birthday.     

白颊长臂猿染色体的研究

本文对我国云南南部的白须长臂猿（Ｈ．ｌｅｕｃｏｇｅｎｙｓ）染色体的Ｇ带、Ｃ带、晚复制带及Ａｇ－ＮＯＲｓ进行了较为详细的研究。它的２ｎ＝５２,核型公式为４４（Ｍ或ＳＭ）＋６（Ａ）,ＸＹ（Ｍ,Ａ）。Ｃ带表明一些染色体着丝点Ｃ带弱化;有的染色体出现插入的和端位的Ｃ带;Ｘ染色体两臂有端位Ｃ带,Ｙ染色体是Ｃ带阳性和晚复制的。Ａｇ－ＮＯＲｓ的数目,雌体有４个,雄体有５个,Ｙ染色体上具ＮＯＲ。本文对白颊长臂猿与其它长臂猿间的亲缘关系、核型进化的可能途径进行了讨论。     

Characterization of silver-stained nucleolus organizer regions (Ag-NORs) in 16 inbred strains of the Norway rat, Rattus norvegicus

Silver-stained nucleolus organizer regions (Ag-NORs) in metaphase chromosomes of cultured fibroblasts were compared among 16 inbred strains of the Norway rat, Rattus norvegicus. Ag-NORs were located at the secondary constrictions or juxtacentromeric regions of the short arms of chromosomes 3, 11, and 12. The frequency and relative size of Ag-NORs were found to be strain-specific, providing a genetic marker system useful for characterization of inbred strains. While considerable cell-to-cell variation was observed within a given strain, the strain-specific pattern of Ag-NORs was shown to be consistent in cultured and noncultured cells obtained from different tissues of embryos, newborns, and adults, as well as in successively cultured cells examined up to the 10th subculture generation. The patterns of Ag-NORs in F1 hybrids made between some of the inbred strains were in general agreement with those expected from the parental strains; some unexpected patterns were noted in F1 hybrids of a particular cross, suggesting the possible existence of nucleolar interactions in such interstrain hybrids, although this has to be confirmed.     

Frequency of Ag-stained nucleolus organizer regions in the acrocentric chromosomes of man

Summary The Ag-stainability of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q-banding of cultured lymphocytes in 51 karyotypically normal persons (31 males and 20 females). A consistent pattern of Ag-positive NORs was found in each individual. Ninety percent of the individuals have a modal number of 8–10 Ag-positive NORs per cell. The frequency of Ag-positive NORs is similar in all five acrocentrics. A statistically nonsignificant lower frequency is found in chromosome 22. Ag-negative NORs on both homologues were found in four cases. The observed frequency distribution of individuals with homozygous NOR-positive, heterozygous, and homozygous negative acrocentric chromosomes was in accordance with the Hardy-Weinberg law in all five pairs of the acrocentric chromosomes as well as in total. No sex difference was observed in our material.A.-V. Mikelsaar is visiting exchange scientist of the Österreichische Bundesministerium für Wissenschaft und Forschung     

准噶尔雅罗鱼染色体核型及带型的初步研究

以肾细胞作材料,采用秋水仙素-低渗-空气干燥法、Ag-NORs、C-带和G-带显带技术对准噶尔雅罗鱼(Leuciscus merzbacheri)染色体进行了研究。结果表明:(1)准噶尔雅罗鱼2n=50,核型组成为18m+14sm+6st+12t,NF=82,没有异型性染色体分化。(2)Ag-NORs的数目在不同的细胞中表现出多态性,数目为1～2个,出现1个Ag-NORs的频率最低(10%),出现2个的频率最高(70%);Ag-NORs主要出现在m1对和m4对同源染色体上;未发现有Ag-NORs联合的现象。(3)准噶尔雅罗鱼的染色体均呈现C-带阳性,可分为着丝粒C-带和端粒C-带。(4)同源染色体上G-带带纹基本一致,其带纹在每对染色体上的数目及分布具有明显特征性。     

Populational polymorphisms in silver staining of nucleolus organizer regions (NORs) in human acrocentric chromosomes

Summary The Ag stainability of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q banding of cultured lymphocytes in 41 karyotypically normal persons (33 males and 8 females) originating from southeast Estonia. The data obtained are compared with those established earlier for a combined Vienna-Ulm population of 51 karyotypically normal persons (see Mikelsaar et al., 1977a). Significant differences between the two populations in the frequency and patterns of Ag-positive NORs were found. The following findings were most striking: the frequency of Ag-positive NORs in chromosome 14 and in the totals was significantly lower in the Estonian population than in the Vienna-Ulm population (P<0.01). The average modal number of Ag-positive NORs per individual was 7.8 in the Estonian population and 8.7 in the Vienna-Ulm sample (P<0.01). If the data of the two populations were combined the frequency of positive NORs was significantly (P<0.05) lower in chromosome 22 than in 13,15, and 21, but not 14.     

黄颡鱼染色体的C─带、Ag—NORs、荧光带和复制带显带的研究

采用Giemas染色、C─带、Ag—NORs、荧光染色和复制带显带的技术对黄颡鱼染色体进行了研究。结果表明,黄颡鱼只有部分的染色体呈现阳性C─带,可分为三类,其中NORs区是染色最深、染色面积最大的区域,为深染居间C─带。其Ag－NORs位于m5q末端。CMA3染色显示NORs区呈现出明亮的荧光。中复制染色体上着丝粒区、端粒区和居间区浅染。发现核仁缢痕、深染居间C─带、Ag—NORs、CMA3明亮区和中复制带浅染NORs区位置基本一致,C─带阳性区和中复制带浅染区具有对应性。     

棕黑锦蛇赤峰亚种染色体组型、C带和Ag-NORs研究

以骨髓细胞为材料研究了棕黑锦蛇赤峰亚种的染色体, 结果表明,该物种的2n=36,由8对大型的和10对微小的染色体组成,AF=50。No.4为性染色体(ZW型);所有大型染色体均显示端粒深染C带,但仅NO.2、3、5和Z染色体显示着丝粒浅染C带。W染色体为整条C带阳性;该物种一对NOR分布于微小染色体。锦蛇属核型可能经历过染色体间的着丝粒融合的罗伯逊易位。 Abstract:This paper reports the karyotype,C-bands and Ag-NORs of Elaphe schrenckii anomala(Boulenger).The diploid number,2n=36,comprising 8 pairs of macro- and 10 pairs of microchromosomes in the E.s.anomala.AF=50.The No.4 is sex chromosome,which belong to ZW type.The C-banding technique revealed telomeric constitutive heterochromatin in the whole macrochromosome.But the centromeric C band was only observed in No.2,3,5 and Z chromosome,while a whole W chromosome is constitutive heterochromatinization.Two NORs was observed in group of microchromosome.     

Satellite association frequency and number of nucleoli depend on cell cycle duration and NOR-activity

Summary In human lymphocyte cultures the frequencies of satellite associations in first, second, and third mitoses were investigated using the BUDR-method. A marked decrease of the association frequency with increasing numbers of cell cycles was found. The number of nucleoli seen in interphase is correlated with the satellite association frequency in the respective metaphase. Satellite association is positively correlated to Ag-staining intensity of the NORs. Individual differences in satellite associations are due to differences in NOR activity and in lymphocyte activation. BUDR diminishes somewhat the Ag-staining intensity of the NORs but has no effect on satellite association frequencies. The main reason for the decrease of satellite association frequency in second and third lymphocyte mitoses is presumably a certain dislocation of the original chromosome position during mitosis and a decreased possibility of association during the short interphases. The high association frequency in first mitosis resembles the chromosome position in the long interphase of G₀-lymphocytes.