Increased satellite association induced by 5′ Bromodeoxyuridine treatment of Phytohemaglutinin-stimulated blood lymphocytes

5'-Bromodeoxyuridine (BrdU) present in the course of late S and G2 phases of the cell cycle in PHA-stimulated human lymphocyte cultures causes the despiralization and elongation of some chromosome regions, including short arms of acrocentric chromosomes. BrdU present at a concentration of 250 microM during the last 10 h in lymphocyte cultures from 19 healthy subjects did not affect the number of silver-stained NORs, but raised significantly the number of satellite associations of acrocentric chromosomes. The mere substitution of thymine by BrdU in DNA strands as a reason for increased number of satellite associations seems a less plausible explanation than the modification of DNA-protein complexes of NOR regions, which could alter the degree of their spiralization and cause the increased tendency of acrocentric chromosomes to associate in the subsequent metaphase.     

Inheritance of Ag-stainability of nucleolus organizer regions

Summary The Ag-stainability of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q-banding in cultured lymphocytes from seven children with trisomy 21 and their parents. The observed Ag-NOR patterns were in accordance with chromosomal inheritance except for a slight intraindividual variation which might be explained mainly by technical causes. In two cases the meiotic nondisjunction could be attributed to one of the parents, once to the father, and once to the mother. It is concluded that the Ag-stainability of the NORs is in general a heritable characteristic of the acrocentric chromosomes in maximally activated cells as, e.g., cultured lymphocytes. It may reflect individual differences in the amount of rDNA as well as differences in the capacity for NOR activation.     

Quantitative studies on the arrangement of human metaphase chromosomes

Summary The association pattern was studied in 2715 mitoses of 90 meningiomas with different numbers of acrocentric chromosomes. In cells with monosomy 22, a significant increase of mitoses with associations was observed in comparison to cells with a normal karyotype. The number of associating acrocentric chromosomes was highly significantly increased. This surplus was not only caused by a highly significant increase of associating G chromosomes but also of D chromosomes. The loss of further acrocentric chromosomes had no significant influence on the number of mitoses with associations or the number of associating chromosomes. Based on the well-known correlations between the nucleolus organization and the association pattern, the results seem to indicate a compensation mechanism among the nucleoles organizing regions (NOR's) which keeps the supply of nucleolar material constant and simultaneously causes a higher association tendency between the remaining acrocentric chromosomes. The increase of associations in the 22 monosomic cells was interpreted as a overcompensation after the loss of only one NOR.     

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.     

Random acrocentric bivalent associations in human pachytene spermatocytes. Molecular implications in the occurrence of Robertsonian translocations

Acrocentric bivalent associations were studied in 232 human male germ cells at pachytene in order to understand better the preferential involvement of chromosomes 13, 14, and 21 in Robertsonian translocations. The tendency of each acrocentric bivalent to associate with another was not correlated with NOR activity, as measured by silver staining. Good agreement was noticed between their ability to associate and the amount of satellite DNA in human acrocentric chromosomes. The distribution of two-by-two acrocentric bivalent associations was random. In order to reconcile this result with the nonrandom distribution of Robertsonian translocations, a molecular hypothesis is proposed. The model is based on homology of recombinational sites, interspersed at regular interval in satellite DNA, which could increase the probability of accidental unequal crossing-over between two specific acrocentric chromosomes.     

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     

Karyotypes of squirrel monkeys (Saimiri sciureus) from different geographic regions

Three different karyotypes have been found so far among Saimiri originating from five different South American localities. All animals examined have the same diploid number (44) of chromosomes but the number of acrocentric and submetacentric chromosomes varies, presumably as a result of pericentric inversions. Saimiri originating from Iquitos, Peru, consistently have ten acrocentric chromosomes; animals originating from Leticia, Colombia, have 12 acrocentric chromosomes. Hybrids produced in our laboratory have the expected 11 acrocentrics and one unpaired submetacentric chromosome. Animals originating from Guyana have fourteen acrocentric chromosomes and the expected two fewer submetacentric chromosomes. Squirrel monkeys from Costa Rica, Panama, and Pucallpa, Peru, studied to this date conform to the Iquitos type with ten acrocentric chromosomes. These findings point to genetic differences which may result in variable responses to laboratory situations. The evolutionary factors involved in this rearrangement of chromosomes and possible influences on phenotypes are subjects of interest for future study. The importance of identifying the source of squirrel monkeys used in biomedical research is apparent if results from different laboratories are to be repeated or compared.     

New insights into the effects of extra nucleolus organizer regions

Summary Chromosome studies were carried out in four members of a sibship with a 15p+chromosome. Two carriers had normal offspring, one was unmarried, and the index case had three abortions and no live children. By means of different banding techniques, up to four satellites and four stalks could be observed on the abnormal chromosome. The Ag-I method showed from zero to four silver precipitates on the 15p+marker. Mean Ag-staining for 15p+and the ten acrocentric chromosomes were obtained in the carriers. Statistically significant differences between sibs were found. These results suggest the existence of: (a) An interindividual and intercellular variation of nucleolus organizer region (NOR) activity in man. (b) An optimal threshold of NOR activity, so that disturbances at the meiotic level could occur when it is exceeded. Our conclusions lead us to advise analysis of NOR activity in individuals with extra nucleolus organizer regions.     

Clonal analysis of the intercellular variability in the functioning of human chromosomal nucleolus organizer regions

Intercellular variability of NOR activity detected with the aid of Ag-staining of human chromosomes was studied in mass and cloned fibroblast cultures obtained from 3 individuals. The intercellular variability was determined by different staining of one of 10 NORs. According to this trait the heterogeneity of the cell population was discovered in all cloned lines, with this heterogeneity being the same as in the parent cultures. That concerned the number of a variable chromosome and the percentage of the cells with Ag-stained and unstained chromosomes. It is suggested that genetic determination in the progenies of the somatic cells concerns the whole spectrum of potential variability observed in cell populations.     

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.     

Distribution of silver-stained nucleolus-organizing regions in the chromosomes of the Equidae

The distribution of silver-stained nucleolus-organizing regions (NORs) in fibroblast chromosomes from all seven extant species of Equidae are described. There are variations in the number and locations of silver-stained NORs in different species but most of the cells in an individual of any speies had only 2 to 4 silver-stained NORs. In Equus przewalskii and E. caballus NORs were detected on up to three different chromosomes. In E. asinus 11 different chromosomes were observed to possess NOR sites. E. hemionus kulan and E. hemionus onager had NORs on 2 large metacentric pairs and a small acrocentric pair. In E. grevyi and E. burchelli NORs were located on 3 to 4 different pairs. E. zebra hartmannae had silver-staining over the telomere regions of the short arms of the chromosomes 1, 3 and 4. A comparison of G-banded chromosomes and silver-stained NORs has revealed one autosome with conserved G-band patterns and possessing a silver-staining NOR in all the species except E. asinus. Variations in the number and multichromosomal locations of NORs in various species could have evolved by pairing and exchanges between non-homologous chromosomal heterochromatin having similar satellite DNA sequences.     

Acrocentric chromosome associations in man.

Heterogeneity among chromosomes was found to be a highly significant source of variation for association proportions, while culture, slide, and observer were negligible sources of variation for association proportions although important for numbers of associations. The consequences of these results for tests of group differences are discussed. It seems evident that each pair of acrocentric chromosomes has its own characteristic probability of entering into association. This is presumably a combination of the probability for each individual member of the pair, a proposition easily tested utilizing acrocentric chromosomes carrying polymorphisms which allow each member of the pair to be individually recognized. A mathematical theory for pairwise satellite association was developed and shown to fit observations on banded chromosomes. While we found very significant heterogeneity among individuals in the frequency with which different chromosomes entered into associations, there was no significant evidence for preferential association between any particular chromosomes, either heterologous or homologous. This finding in our material of apparently random associations between different chromosomes is contrary to claims made by other investigators and should be tested on other material. No correlation was found between the phenotype of the chromosome, as judged by cytogenetic polymorphisms, and its probability of association.     

Trisomy 8p: unusual origin detected by fluorescence in situ hybridization

Summary Chromosomal analysis of a neonate with brain and heart abnormalities revealed trisomy for 8p. The mother's karyotype showed 47 chromosomes with one chromosome 8 being represented as two separate chromosomes, an acrocentric 8p and a telocentric 8q. Gbanding and silver staining revealed a satellite and nucleolus organizing region (NOR) on the 8p. Centromericspecific probes to the centromeres of chromosomes 8, 15, 13/21, 22 and the acrocentric chromosomes revealed that only the 8q centromere was of chromosome-8 origin, while the 8p centromere was of chromosome-14 origin.     

Translocation t(22;22)(p11.1;q11.1) and NOR studies in a female with a history of repeated fetal loss.

A 32-year-old phenotypic female with a history of nine consecutive abortions each in the first trimester was referred for cytogenetic studies. She was found to have 45,XX,t(22;22) (p11.1;q11.1) chromosomal pattern. The Ag-NOR banding technique showed that the NORs of both the acrocentrics involved in the translocation were deleted and the loss suffered from the elimination was compensated by the increased NOR activity as well as presence of dNOR on other acrocentric chromosomes.     

Distribution of chromosomal polymorphisms in three subspecies of squirrel monkeys (genus Saimiri)

The presence of nucleolar organizer regions (NORs) and C-band polymorphisms has been examined in three subspecies of squirrel monkeys, Saimiri sciureus sciureus, S. boliviensis boliviensis, and S. boliviensis peruviensis. Pericentric inversions in chromosomes 15 and 16 were also examined in the three groups. Chromosome 15 was acrocentric in S. s. sciureus and submetacentric in S.b. boliviensis and S.b. peruviensis. Chromosome 16 was acrocentric in S.s. sciureus and S.b. boliviensis while being submetacentric in S.b. peruviensis. There was a significant difference in the distribution of the C-band polymorphisms on chromosomes 5 and 14 in the three groups, as determined by Chi-square analysis, while no difference was observed in the distribution of the NOR polymorphism on chromosome 2. The NOR polymorphism and the interstitial C-band polymorphism of chromosome 14 were found in all three groups; the C-band polymorphism of chromosome 5 was found only in S.s. sciureus. Twelve pedigreed families were examined. Pedigree analyses were consistent with codominant inheritance of each polymorphism. The results of these cytogenetic studies in squirrel monkeys are pertinent to genetic management and research protocols.     

Expression of nucleolus organizer regions (NORs) in human acrocentric chromosomes by NSG, QFQ and RFA techniques: are they identical?

The morphology of nucleolus organizer regions (NORs) of human acrocentric chromosomes has been studied in a family by QFQ, RFA, and NSG banding techniques. The pale green colour seen by RFA was found darkly stained by NSG. However, in some instances, NOR regions were expressed by NSG technique but the pale green colour was not seen. Therefore, it is concluded that there is no direct relationship between a heteromorphism identified by one technique and that identified by another.     

Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon

Cichla monoculus, Cichla temensis (peacock bass or tucunare), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatuma (C. monoculus, C. temensis and their natural hybrid), Jau (C. temensis), and Solimoes rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n=48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla.     

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.     

Note on the karyotype and NOR phenotype of leuciscine fish Acanthobrama marmid (Osteichthyes, Cyprinidae)

The karyotype and major ribosomal sites as revealed using silver staining of Anatolian leuciscine cyprinid fish Acanthobrama marmid were studied. The diploid chromosome number was invariably 2n = 50. Karyotype consisted of eight pairs of metacentric, 13 pairs of submetacentric and four pairs of subtelocentric to acrocentric chromosomes. The largest chromosome pair of the complement was subtelo-to acrocentric characteristically, which is a characteristic cytotaxonomic marker for representatives of the cyprinid lineage Leuciscinae. The nucleolar organizer regions (NORs) were detected in the telomeres of two pairs of medium sized submeta-to subtelocentric chromosomes. No heteromorphic sex chromosomes were found. The karyotype pattern of A. marmid is nearly identical to that found in most other representatives of the Eurasian leuciscine cyprinids, while the multiple NOR phenotype appears to be more derived as opposed to a uniform one, ubiquitous in this group.