Different behaviour of Xbb+ and Xbb chromosomes in D. melanogaster with only one nucleolus organizer.

Summary We have examined the rDNA content of male and female adult flies having only one nucleolus organizer (NO), using X chromosomes carrying wild or partially deleted bobbed loci (Xbb⁺/O, Xbb⁺/X_NO-and Xbb/O, Xbb/X_NO^-).The results show that in Xbb⁺/O and Xbb⁺/X_NO^-flies, where only somatic gene compensation is supposed to occur, the rDNA increase, although less pronounced than previously reported, is directly proportional to the number of rRNA genes initially present in the nucleolus organizer. In Xbb/O and in Xbb/X_NO^-flies the rDNA increase is relatively much higher than that observed in flies carrying bb⁺ instead of bb. It is suggested that this may be due to rDNA premagnification and somatic gene compensation occurring simultaneously in the former flies.On leave of absence from International Institute of Genetics and Biophysics, Naples, Italy     

Frequency of Ag-stained nucleolus organizer regions in the chromosomes of cattle

Sequential Ag NOR/G-band studies were performed on the chromosomes of 33 Austrian Al bulls. The mean number of Ag-NORs per bull karyotype was 6.06. The distribution of Ag-NORs was found to be characteristic for each individual.     

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     

Behavior of the nucleolus organizer regions of the chromosomes in polykaryocytes consisting of micronuclei

The nucleolar organizer regions (NORs) of Chinese hamster chromosomes (clone 237, cell line BIId-ii-FAF28) were studied in mononuclear cells and polykaryocytes induced with colcemid. The chromosomes with NORs were marked as 1, 2, 3, 4. The activity of NORs in mononuclear cells was higher in chromosomes 1, 2, 3. The associations of NORs were observed between chromosomes I and 2 (3% of all metaphases). In polykaryocytes the chromosomal pairs 1, 2, 3 showed different NOR activity in different metaphases. The associations of NORs in pairs of chromosome I were found in 51.3% of cases. The associations of NORs in pairs of chromosome 2 were observed in 7.5% of cases. This method may be used for the estimation of association potency of NORs in chromosomes.     

Differential giemsa staining of kinetochores and nucleolus organizer heterochromatin in mitotic chromosomes of higher plants

Differential Giemsa staining techniques have been used to stain kinetochores and nucleolus organizer heterochromatin in four species of higher plants. Using these techniques it has been possible to follow developmental changes of kinetochores through mitosis. In addition, these same techniques also have allowed the determination of the number and sites of nucleolus organizers in the various chromosome complements studied.     

Quantitative characteristics of the nucleolus organizer region of the chromosomes in the domestic pig

Absolute and relative dimensions of Ag+-NORs and secondary constrictions (SC) of pig chromosomes were determined. Interchromosomal and interindividual variability of these indices were marked. An attempt was undertaken to standardize the absolute sizes of Ag+-NORs and SC, degrees of chromosome condensation being taken into consideration. A high correlation between the dimensions of Ag+-NOR and of SC was noted.     

Sterility in hybrid cattle. I. Distribution of constitutive heterochromatin and nucleolus organizer regions in somatic and meiotic chromosomes.

The distribution of constitutive heterochromatin and nucleolus organizer regions (NOR's) in somatic as well as in meiotic chromosomes of Bos taurus, Bos banteng, Bison bison, and their hybrids are analyzed. C-bands are present in the centromeric regions of every autosome. The X chromosome does not show a distinct C-band in the centromeric region, whereas the Y chromosome contains an appreciable amount of C-band material. In somatic metaphases, NOR's are present on the telomeric ends of five pairs of autosomes. During pachytene, five autosomal bivalents contain NOR's on their terminal ends. Meiotic preparations made from sterile bulls did not contain stages beyond the degenerating pachytene, which are C-banding, more frequently showed clustering of heterochromatin than did the pachytene stage in normal bulls.     

Association of nucleolus organizer chromosomes in domestic sheep (Ovis aries) shown by silver staining.

The nucleolus organizer regions of domestic sheep (Ovis aries), as shown by silver staining, are located terminally on chromosomes 1, 2, 3, 4, and 25. Significant differences between individuals in the number of Ag-NORs per cell were found. The frequency of involvement of individual chromosome pairs in nucleolar organization was found to be a characteristic of individual animals. Association frequencies of individual chromosomes were accounted for by their frequency of participation in nucleolar organization. No evidence for nonrandom association of chromosome pairs was found.     

Simultaneous activity of nucleolus organizer regions of human and Chinese hamster chromosomes in somatic cell hybrids

In an interspecific human-Chinese hamster hybrid that retains 13 and 85.6% of the chromosomes of each parental complement, activity of nucleolus-organizing regions (NOR) of both type chromosomes is observed in 18.9% of the cells. Interspecific chromosomal associations are also noted. Unlike the parental lines of Chinese hamster cells, the hybrids show the associations of the NOR of Chinese hamster chromosomes. In hybrid cells, there occurs partial suppression of NOR activity in human and Chinese hamster chromosomes, while the NOR of the 3d chromosome of the Chinese hamster is completely suppressed.     

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.     

A rapid technique for producing silver-stained nucleolus organizer regions and trypsin-Giemsa bands on human chromosomes

Summary A simple and rapid technique is described whereby the nucleolus organizer regions (NORs) of human chromosomes can be differentially stained with silver. This staining is followed by trypsin-Giemsa banding on the same metaphase chromosomes. The metaphases simultaneously exhibit silverstained NORs and G bands, allowing for the unequivocal identification of all chromosomes and greatly facilitating studies involving the NOR-bearing acrocentrics.     

Detection of nucleolus organizer regions in chromosomes of human,chimpanzee, gorilla,orangutan and gibbon

Nucleolus organizer regions were detected by the Ag-AS silver method in fixed metaphase chromosomes from human and primates. In the human, silver was deposited in the secondary constriction of a maximum of five pairs of acrocentric chromosomes: 13, 14, 15, 21 and 22. The chimpanzee also had five pairs of acrocentric chromosomes stained, corresponding to human numbers 13, 14, 18, 21 and 22. A gibbon had a single pair of chromosomes with a secondary constriction, which corresponded to the nucleolus organizer region. In each case the Ag-AS method detected the sites which have been shown by in situ hybridization to contain the ribosomal RNA genes. An orangutan had eight pairs of acrocentric chromosomes stained with Ag-AS, probably corresponding to human numbers 13, 14, 15, 18, 21 and 22, plus two others. Two gorillas had silver stain over two pairs of small acrocentric chromosomes and at the telomere of one chromosome 1. The larger gorilla acrocentric chromosomes had no silver stain although they all had secondary constrictions and entered into satellite associations.     

X chromosome nucleolus organizer mutants which alter major type I repeat multiplicity in Drosophila melanogaster

The nucleolus organizer (NO) of the D. melanogaster X chromosome is composed of ribosomal repeat units which contain two types (I and II) of non-rDNA insertions (In+) and repeats with no insertions (In-). Evidence from other laboratories indicate random interspersion of all types of repeat units within the X NO. An EcoRI and BamHI examination of rDNA from two bobbed mutants, bb2rI and mal12 demonstrates segregation of the major type I repeat units. The 46 rDNA repeats of the bb2rI NO contain no detectable major type I repeats whereas the majority of the 68 rDNA mal12 repeats are major type I and tandemly linked. This observation suggests that gross deletions of rDNA can result in nucleolus organizer regions with predominantly one type of repeat unit. Additivity tests demonstrate that the 46 ribosomal repeats of the bb2rI chromosome revert the phenotype of other bobbed NOs, but the 68 mal12 ribosomal repeats show no or slight additivity. This is in agreement with the observation that In+ repeats do not significantly contribute to functional rRNA. A Southern blot analysis using BamHI which cuts only in type I insertions demonstrates that the majority of major type I In+ repeating units exist in tandem linkage group(s) within the X NO.     

Ag-staining of nucleolus organizer regions of chromosomes after A-,C-, G-, or R-banding procedures.

Metaphase chromosome preparations were made from leukocyte cultures of normal individuals. The cells were fixed in methanol:acetic acid (3:1 v/v), then dropped on cold, wet slides which were air-dried before storage at 4 degrees C. The slides were stained to identify the chromosomes by one of the following procedures: (1) Quinacrine. Slides were stained for 10 min in quinacrine mustard solution, rinsed in running tap water for 2 min, and mounted in Tris-maleat buffer, pH 5.6.     

Ag-staining of nucleolus organizer regions on human prematurely condensed chromosomes from cells with different ribosomal RNA gene activity

The Ag-staining of the nucleolus organizer regions (NORs) of prematurely condensed chromosomes (PCCs) of human cells showing different degrees of rRNA-gene activity clearly indicates a close correlation between the positive Ag-staining of NORs and the activity of rRNA genes. The Ag-stain, however, seems insensitive to low rates of rRNA synthesis and obviously follows a threshold reaction. Furthermore it was found that the frequency of Ag-positive chromosomes involved in satellite associations in interphase does not differ from that in metaphase.