Frequency and non random distribution of silver-staining NORs on acrocentric chromosomes from neonate and adult human lymphocytes

The NORs frequency in a group of newborns and adults was determined by the gelatine silver staining technique. A higher number of Ag-NORs (χ² test, p<0.01) was found in adults than in newborns. The lack of correlation between cell proliferating rate index (PRI) and frequency of Ag-NORs let us suppose that the decrease of Ag-positive NORs in neonates could probably be due to factors different from cell kinetics. A non random distribution of Ag-NORs on the acrocentric chromosomes was also demonstrated: chromosome 21, in particular, showed the highest frequency, while chromosome 15, the lowest.     

Preferential association of nucleolar organizing human chromosomes as revealed by silver staining technique at mitosis

Summary The frequency of different types of satellite associations of nucleolar organizing human chromosomes (i.e. acrocentric chromosomes; 13, 14, 15, 21, and 22) is reported using 10 normal individuals by Ag-staining technique. The preferential involvement of acrocentric chromosomes in satellite association is suggested. Only acrocentric chromosomes with active NORs (i.e. Ag-stained) were found in association while unstained (inactive NORs) chromosomes were never seen in satellite association. In general as number of NORs expression increase, the frequency of association per cell was also increased. A possible mechanism and the clinical consequences of such an unusual phenophenon is described.     

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.     

Polymorphisms of Ag-stained nucleolar organizer regions in man

Summary Polymorphisms of the NORs as tested by Ag-staining of metaphase G-banded chromosomes were investigated in cultured blood lymphocytes of karyotypically normal individuals from the Moscow population.The study of cell-to-cell variability in the number of Ag-stained NORs carried out on 14 monozygotic twin pairs showed the phenomenon to have some features of real intercellular variation.In 40 unrelated individuals the individual acrocentric chromosomes were compared by the number of Ag-stained NORs, their degree of staining, and their participation in acrocentric association. Chromosome 21 was found to be significantly more active than four others by all the criteria, and chromosome 15 was less active compared with the others by the size of the Ag deposits and the frequency of participation in NOR associations. The frequency distribution of homozygotes and heterozygotes for Ag-stained NORs in the same group of 40 individuals was in accordance with the Hardy-Weinberg law.     

Chromosome banding and molecular cytogenetic study of two Mediterranean trachinoid fish species (Teleostei: Trachinidae, Uranoscopidae)

The chromosomes of Echiichthys vipera (Trachinidae) and Uranoscopus scaber (Uranoscopidae) were analyzed by means of various banding methods and fluorescence in situ hybridization (FISH) with telomeric and major rDNA probes, respectively. The karyotype of E. vipera was composed of 48 acrocentric chromosomes and NOR sites, as revealed by all detection methods, were situated pericentromerically on a single pair of middle-sized chromosomes. Blocks of constitutive heterochromatin were present in the pericentromeric regions of all pairs of chromosomes. The karyotype of U. scaber showed three karyomorphs: 2n = 30 (18 m + 12 a/st [m = metacentric, a = acrocentric and st = subtelocentric]), 2n = 28 (20 m + 8 a/st), 2n = 27 (21 m + 6 a/st). NORs, as revealed by FISH, were situated pericentromerically on a single pair of middle-sized chromosomes in spite of Ag-positive signals in the centromeres of all pairs of chromosomes. Robertsonian fusions were hypothesized for observed variation due to invariable number of chromosome arms FN = 48.     

Expression of Ribosomal Cistrons of Human Chromosomes at High Resolution

The expression of ribosomal cistrons in the nucleolar organizer regions (NORs) has been studied with high resolution banding in the acrocentric chromosomes of 10 normal individuals. It was found that if a particular chromosome did not stain with silver nitrate at metaphase, then it did not stain at prophase either. Therefore, it is concluded that some of the acrocentric chromosomes have variable expression of NORs.     

Expression of ribosomal cistrons of human chromosomes at high resolution

The expression of ribosomal cistrons in the nucleolar organizer regions (NORs) has been studied with high resolution banding in the acrocentric chromosomes of 10 normal individuals. It was found that if a particular chromosome did not stain with silver nitrate at metaphase, then it did not stain at prophase either. Therefore, it is concluded that some of the acrocentric chromosomes have variable expression of NORs.     

A karyotype analysis of the genus Dicentrarchus by different staining techniques

This study presents a cytogenetic analysis of the genus Dicentrarchus , represented by two species, D. labrax and D. punctatus . The karyotypes are very similar, even after staining with different techniques. Both species show 48 subtelocentric and acrocentric chromosomes, gradually decreasing in size. One pair of small size chromosomes has heteropycnotic and heteromorphtc short arms of longer size. These short arms are C- and Ag-positive, i.e. nucleolar organizer regions, NORs, are located there. Constitutive heterochromatin is also evident as a subcentromeric band on the long arms of a large chromosome pair. CMA₃-staining confirms the location and the heteromorphism of NORs. DAPI and quinacrine produce homogeneous staining of chromosomes. A review of cytogenetic studies on 'serranid' species is also presented.     

Genetic determination of NOR activity in human lymphocytes from twins

Summary Activity of nucleolar organizer regions (NORs) was studied in cultured blood lymphocytes from 20 monozygotic (MZ) and 20 dizygotic (DZ) twin pairs. The number of Agstained NORs, the degree of staining, and the frequency of acrocentric associations were used as criteria of the NOR activity, the acrocentric chromosomes being identified by G-banding. Analysis of intrapair concordance as well as of intrapair variance showed the number of Ag+NORs and the size of Ag-deposits to be highly heritable traits. Intrapair differences in acrocentric association frequency were not significantly higher in DZ compared with MZ twins.     

Comparison of silver staining of nucleolus organizer regions in human lymphocytes and fibroblasts

Summary Ag-staining of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q-banding in repeated lymphocyte and skin fibroblast cultures from three different individuals. A similar pattern of Ag-stainability of NORs was found in the two tissues in each individual. Small differences concerning, in each case, only one of the acrocentric chromosomes were found between repeated lymphocyte cultures, as well as between lymphocyte and fibroblast cultures of the same individual without indication of any prevalence of one tissue type in a certain direction. The possibility that these differences are caused by different stages of NOR activation is discussed.     

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.     

Chromosome banding studies in an Indian mullet: evidence of structural rearrangements from NOR locations

C-, G- and NOR bands have been studied in the female sex of Rhinomugil corsula. (Mugilidae, Pisces) by deploying the conventional methodologies with suitable modifications of minor nature. The diploid metaphase complements contained 48 acrocentric chromosomes. The localization of C-band heterochromatin was found to be mostly at or near the centromeric regions of the acrocentric chromosomes. The G-type bands were not so well defined, but some of the G-banded chromosomes also contained C-bands. Interestingly, silver-positive NORs were found at the telomeric ends of five acrocentric chromosomes, including one homologous pair having NORs in both chromatids, while one chromosome showed NORs in both of its chromatids and the other two had only one NOR localized at one of its chromatids. This would suggest that one homologue of the second pair of NOR-bearing chromosomes possibly underwent a chromatid exchange with a non-NOR bearing chromosome. This is quite a unique situation not reported earlier in any species of fish., though some other form of NOR-polymorphism/heteromorphism has rarely been reported. Therefore, further exploration in natural populations of this species to examine the other sex and to verify if there also exists other chromosomally polymorphic races (in respect of NOR-polymorphism) of this species, would be rewarding.     

Population polymorphism of silver-stained nucleolar organizer chromosome regions in man

Activity of nucleolar organizer regions (NORs) of acrocentric chromosomes determined by Ag-staining was comparatively studied in 40 individuals of Bulgarian and 40 individuals of Russian populations. Chromosome 21 was found to be significantly more often stained in both populations. The other NORs did not differ significantly in staining from the means. No differences were noted between individual NORs, in respect of the intensity of Ag-staining in both populations, except chromosome 15 which showed markedly decreased staining capacity in Russians. The data obtained are compared with those published in literature concerning four other populations.     

Cytogenetic analyses of a Salvelinus hybrid reveal an evolutionary relationship between the parental species

Mitotic analyses of the brook trout (Salvelinus fontinalis) x arctic char (S. alpinus) hybrids (sparctic trout) revealed a mode of 2n = 82 with 18 metacentric and 64 acrocentric chromosomes. The brook trout had 2n = 84 with 16 metacentric chromosomes and the arctic char had 2n = 80 with 20 metacentric chromosomes; both species are derivatives of a single tetraploid event. Variable multivalent-like configurations that may be centromeric associations of bivalents were observed in C-banded pachytene figures of female sparctic trout. Metaphase I analyses of sparctic trout males indicated that two fusions of nonhomologous acrocentric chromosomes representing two duplicated chromosome sets must have occurred in the arctic char after its evolutionary divergence from the brook trout. A mode of seven tetravalent rods per cell suggests that preferential multivalent pairing occurs in the sparctic hybrid; metaphase I analyses of S. alpinus males revealed a mode of only five tetravalent rods per cell. The presence of multivalents implies that the arctic char, like the brook trout, is still undergoing diploidization. Cytochemical detection of the nucleolar organizer region (NOR) revealed intra- and interspecific as well as intraindividual variability in the numbers and types of chromosomes (metacentric or acrocentric) on which NORs appeared in arctic char and sparctic trout. Brook trout only had NORs on acrocentric chromosomes. This may indicate that different chromosomal fusions occurred in the evolution of brook trout from arctic char.     

Human tumor and rodent-human hybrid cells with an increased number of active human NORs.

A human fibrosarcoma line, HT1080-6TG, with a near diploid number of chromosomes, has an average of 7.3 chromosomes with an Ag-stained nucleolus organizer region (NOR). Cells of this line with an increased number of chromosomes have an increased number of Ag-stained NORs. This cell line has been used as the human parent in constructing mouse-human and rat-human hybrids that segregate rodent chromosomes. The hybrid ccell lines, which have 100 or more chromosomes per cell, show a proportionate increase in the number of Ag-stained NORs (means, 11.4--16.8). The frequency of association of acrocentric chromosomes increases in a similar fashion. There is no evidence of inactivation of human NORs in these cells.     

Polymorphism of Ag-stained nucleolus organizer regions in lymphocytes of patients with ovarian or breast adenocarcinoma

Summary The Ag-stainability of nucleolus organizer regions (NORs) in the acrocentric chromosomes identified by Q-banding was studied in 45 female patients with adenocarcinoma of the ovary or breast and in 45 healthy females. Significantly higher frequencies of Ag(+)NORs per individual (8.8 and 8.3; P<0.05), in the G group chromosomes (3.6 and 3.2; P<0.05), and in chromosome 21 (1.9 and 1.7; P<0.02) were found in patients, compared with controls. Despite the lack of significant differences in NORs between the groups of patients with ovarian and breast adenocarcinoma, the main difference between the patients and controls was due to the patients with adenocarcinoma of the ovary, where a significantly higher frequency of Ag(+)NORs was found in chromosomes 21 (P<0.01) and 13 (P<0.05).     

Karyotype and divergence of stream Dolly Varden from the Southern Sakhalin

The karyotype of stream Dolly Varden inhabiting a tributary of the Belaya River (the basin of Naiba River, southern Sakhalin) was determined (2n = 82 and NF = 98 + 2). According to the main characteristics (chromosome number and arm number, the presence of a pair of marker submeta-subtelocentric chromosomes with nucleolus organizer regions (NORs), one pair of large acrocentric chromosomes, and one pair of subtelocentric chromosomes), this karyotype is identical to the karyotype of anadromous southern Dolly Varden from Salvelinus malma krasheninnikovi of Primorye and Japan. However, in most stream Dolly Varden individuals, additional active nucleolus organizer regions (NORs) located in telomeric and paracentric regions of two to three pairs of acrocentric chromosomes were revealed. It is suggested that the stream and anadromous southern forms of Dolly Varden are evolutionarily related NORs that are silent in the anadromous souther form are active in the stream form. Possible causes of these differences in NOR activity are discussed.     

Karyotype, Ag-NOR, CMA3 and SEM studies in a fish (Mystus tengara, Bagridae) with indication of female heterogamety

Somatic karyotypes in M. tengara contained 54 chromosomes, comprising 26 homomorphic pairs in both sexes and one pair of heteromorphic nature in female (one big submetacentric and one small subtelocentric chromosomes), while in males this pair was homomorphic (with two big sub-metacentric chromosomes). The Nucleolus Organizer Regions (NORs) were located at one arm of the suspected sex elements in both sexes, while another pair of metacentric chromosomes (No.7) also showed Ag-positive arm. The CMA3 technique revealed relatively bright fluorescing zones in the regions of chromosomes that showed Ag-positive staining, revealing thereby the preponderance of GC-rich active sites of rRNA genes in NORs. SEM studies revealed clear heteromorphism to exist in the elements suspected as sex chromosomes in females.