Distribution Of Nucleolar Organizer Regions Research Articles

Systematic relationships within the Microtus arvalis (Rodentia: Cricetidae) group in Iran, inferred from cytogenetic analyses

The distribution of C-heterochromatin and nucleolar organizer regions (NORs) was studied in three species of voles of the Microtus arvalis group in Iran: M. mystacinus, M. kermanensis, and M. transcaspicus. The C-banding pattern and NORs distribution were similar in M. mystacinus and M. kermanensis suggesting taxonomic proximity of these two species. At the same time, the karyotypes of M. mystacinus from Iran were different in C-banding pattern from the complements of conspecific 54-chromosome voles from Europe and other regions of Asia. The most distinct difference was in size of the distal C-positive block of heterochromatin on the X chromosome. In this respect M. mystacinus from Iran and M. kermanensis resembled M. transcaspicus. Small size of the distal C-positive heterochromatic block may be ancestral whereas larger size is derived. The X chromosome of M. transcaspicus can be derived from that of M. mystacinus and M. kermanensis by a large inversion or centromeric shift.

Molecular cytogenetic analyses of Epinephelus bruneus and Epinephelus moara (Perciformes, Epinephelidae).

Genus Epinephelus (Perciformes, Epinephelidae), commonly known as groupers, are usually difficult in species identification for the lack and/or change of morphological specialization. In this study, molecular cytogenetic analyses were firstly performed to identify the closely related species Epinephelus bruneus and E. moara in this genus. The species-specific differences of both fish species showed in karyotype, chromosomal distribution of nucleolar organizer regions (NORs) and localization of 18S rDNA. The heterochromatin (interstitial C-bands) and distribution pattern of telomere (TTAGGG)n in E. bruneus revealed the chromosomal rearrangements and different karyotypic evolutionary characteristics compared to those in E. moara. The cytogenetic data suggested that the lineages of E. bruneus and E. moara were recently derived within the genus Epinephelus, and E. moara exhibited more plesiomorphic features than E. bruneus. All results confirmed that E. moara, which has long been considered a synonym of E. bruneus, is a distinct species in the family Epinephelidae. In addition, molecular cytogenetic analyses are useful in species differentiation and phylogenetic reconstruction in groupers.

Nucleolar organizer region distribution in Nannospalax ehrenbergi (Nehring, 1898) (Rodentia: Spalacidae) from Iraq

The distribution of nucleolar organizer regions (NORs) in Nannospalax ehrenbergi from Iraq was determined for the first time. In the karyotype of N. ehrenbergi the diploid number, fundamental number, and fundamental autosomal number were 52, 76, and 72, respectively. NORs occur in the telomeric regions of submetacentric and acrocentric autosome pairs.

Karyotypes and Sex Ratios in Populations of Eubranchipus Grubii (Dybowski, 1860) and Branchipus Schaefferi Fischer, 1834 (Branchiopoda, Anostraca) from Poland

Two populations of the fairy shrimp Eubranchipus grubii (Dybowski, 1860) and one population of Branchipus schaefferi Fischer, 1834 from Poland were studied cytogenetically. The aim was to confirm their diploid chromosome numbers and chromosome morphology, as well as to reveal the distribution of nucleolar organizer regions (NORs) and the course of meiosis. The first species exhibited 24 small chromosomes in both sexes, while the latter showed 2n = 20 in both males and females. In E. grubii, female meiosis involved a “diffuse stage” characterized by decondensation of chromatin, and positive heteropycnosis (after staining by Giemsa) of one bivalent. The morphology of the plates of the second meiotic division suggests the chromosomes in both species are monocentric (prevailingly bi-armed). Nevertheless, constitutive heterochromatin has not been visualized by C-banding. Silver staining revealed 3 pairs of nucleolar organizer regions (NOR) in B. schaefferi, while in E. grubii the detection of NORs failed. In contrast to some previous studies reporting supernumerary chromosomes (B chromosomes) as sex ratio distorters in B. schaefferi, we failed to observe any B chromosomes in the populations under study. We suggest the fluctuation of sex ratios as found in the local populations, would rather be influenced by the environment.

Variation in C-heterochromatin and NOR distribution among chromosomal races of mole rats (Spalacidae) from Central Anatolia, Turkey

In this study, the 2n=40, 58, 60 chromosome races of mole rats of the Nannospalax nehringi superspecies from the Konya province in Turkey were investigated. Conventional chromosome staining, Ag-NOR staining and C-banding analysis was carried out on 25 specimens of mole rats from 13 localities. The description of conventional karyotypes revealed the detailed pattern of geographic distribution of individual races of mole rats in Central Anatolia. The C-positive regions were localized in centromeric areas, and/or in short arms of submetacentric and subtelocentric autosomes. In the 2n=40 race, C-heterochromatin regions were found in whole short arms of four biarmed autosomal pairs whereas C-heterochromatin was localized in pericentromeric areas of biarmed and acrocentric autosomes in the karyotypes of the other races. Autosomal pairs heteromorphic possibly due to deletion/addition of heterochromatin and euchromatin material in short arms were recorded in some populations of both the 2n=58 and 60 chromosome races. The distribution of nucleolar organizer regions (NORs) was described for the first time in the 2n=40 and 58 races. The NORs were localized in four pairs of biarmed autosomes in all the studied chromosomal races in distal heterochromatic and euchromatic areas of the short arms. The results demonstrate the considerable extent of variation in C-heterochromatin and NORs distribution in karyotypes of mole rats from Anatolia.

Nucleolar organizer regions (NORs) in Cricetulus migratorius (Pallas, 1773) and Meriones tristrami Thomas, 1892 (Mammalia: Rodentia) from Central Anatolia

The distribution of nucleolar organizer regions (NORs) in Cricetulus migratorius and Meriones tristrami from Central Anatolia was determined. In the karyotype of Cricetulus migratorius the diploid number, fundamental number, and fundamental autosomal number are 22, 44, and 40, respectively. The diploid number, fundamental number, and fundamental autosomal number of Meriones tristrami are 72, 84, and 80, respectively. In Cricetulus migratorius, NORs occur in the telomeric regions of metacentric and subtelocentric autosome pairs. Furthermore, terminally located NORs in metacentric and acrocentric autosomes of Meriones tristrami are presented in this present paper.

Karyotypic variation between wood mouse species: banded chromosomes ofApodemus alpicola andA. microps

The banding pattern (G-, C-, AgNOR-staining) was described in karyotypes ofApodemus alpicola Heinrich, 1952 andA. microps Kratochvil et Rosicky, 1952 collected from the Alps and central Europe. Distinct differences between the two species were revealed in the distribution of C-heterochromatic regions in autosomes and the sex chromosomes, and the distribution of nucleolar organizer regions (NORs). Extensive variation in the distribution pattern of C-heterochromatin and NORs obviously exists among the wood mice of the subgenusSylvaemus, and individual species can be distinguished according to a specific variation pattern. However, it seems premature to designate individual karyotypic forms as separate species, because the extent of overall geographical interpopulation variation is still not sufficiently known.

A molecular cytogenetic analysis of the tribe Bovini (Artiodactyla: Bovidae: Bovinae) with an emphasis on sex chromosome morphology and NOR distribution.

Q-band comparisons were made among representative species of the four genera of the tribe Bovini (Bos, Bison, Bubalus, Syncerus) as well as to selected outgroup taxa representing the remaining two tribes of the subfamily Bovinae (nilgai, Boselaphini; eland, Tragelphini), the Bovidae subfamily Caprinae (domestic sheep) and the family Cervidae (sika deer and white-tailed deer). Extensive autosomal arm homologies were noted, but relatively few derivative character states were shared. Focus was then made on variation of the sex chromosomes and the chromosomal distribution of nucleolar organizer regions (NORs). Bovine BAC clones were used in molecular cytogenetic analyses to decipher rearrangements of the sex chromosomes, and a pocket gopher 28s ribosomal probe was used to map the chromosomal locations of nucleolar organizing regions (NORs). Some of the more noteworthy conclusions drawn from the comparative analysis were that: 1. The Bovidae ancestral X chromosome was probably acrocentric and similar to acrocentric X chromosomes of the Bovinae; 2. The domestic sheep acrocentric X is probably a derivative character state that unites non-Bovinae subfamilies; 3. Bos and Bison are united within the tribe Bovini by the presence of shared derivative submetacentric X chromosomes; 4. Sika and white-tailed deer X chromosomes differ by inversion from X chromosomes of the Bovinae; 5. The Bovini ancestral Y chromosome was probably a small acrocentric; 6. Bos taurus, B. gaurus and B. banteng share derivative metacentric Y chromosomes; 7. Syncerus and Bubalus are united by the acquisition of X-specific repetitive DNA sequence on their Y chromosomes; 8. Bovinae and Cervidae X chromosome centromere position varies without concomitant change in locus order. Preliminary data indicate that a knowledge of the chromosomal distribution of NORs among the Bovidae will prove to be phylogenetically informative.

Silver staining method for nucleolar organizer regions in cervical smears.

The distribution of nucleolar organizer regions (NORs) was studied in Papanicolaou preparations of cervical smears in order to distinguish benign from preneoplastic lesions. Destained smears (six defined as normal, six as inflammatory with squamous metaplasia, six as CIN I, six as CIN II, and five as CIN III) were submitted to the Ag-NOR method after staining with Orange G and EA36. Ag-NOR count was performed in previously outlined fields on the smears. Statistically significant differences (P < .05) were found between the normal smears, inflammatory smears with squamous metaplasia, and each grade of CIN. We conclude that the Ag-NOR technique could be useful to evaluate cervical smears of doubtful interpretation, using previous demarcation of the abnormal fields/cells.

Interphase nucleolar organizer region distribution in the tissues of oral leukoplakia, oral submucous fibrosis and oral cancer

The AgNOR technique, was applied to oral tissue sections of 185 oral cancer, 42 oral leukoplakia, 37 oral submucous fibrosis and 10 normal subjects to investigate whether any correlation held good in these different tissues. Compared to the AgNOR counts in normal oral epithelium, there was a gradation in increase in the mean AgNOR counts from oral leukoplakia to oral submucous fibrosis to oral carcinoma (P<0.01). This suggests that AgNOR count parallels with the degree of neoplastic transformation of oral epithelium. Three oral submucous fibrosis patients who showed very high AgNOR counts as that of oral cancer patients, later developed oral carcinoma. Among the oral cancer tissues, the moderately and poorly differentiated subtypes showed higher AgNOR counts and scattered distribution pattern than the well differentiated subtype which showed a clustered distribution pattern. These results suggest that AgNOR technique can be utilised as a diagnostic and prognostic indicator in premalignant and malignant oral tissues.

Cytogenetic peculiarities in the Algerian hedgehog: silver stains not only NORs but also heterochromatic blocks

Hedgehogs belong to one of the several mammalian taxa in which karyotype differences are based on variations in heterochromatin content. Furthermore, the number and location of nucleolar organizer regions (NORs) can also vary widely. In the present study these cytogenetic features were investigated in the Algerian hedgehog, Erinaceus (Aethechinus) algirus. The heterochromatin and NOR distribution patterns in the karyotype of this species are new among hedgehogs, whereas the euchromatic regions, including their G-band pattern, are similar to those reported by others. In addition, silver staining revealed a cytogenetic feature exclusive to the heterochromatic blocks of E. algirus: their silver staining with standard cytogenetic procedures. Because no similar phenomenon has been described previously in a mammalian species, several hypotheses about the significance and specificity of silver staining to NOR sites are discussed. Finally, the existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechanism which permits the accumulation of heterochromatin on specific chromosomes, rather than the heterochromatin itself.

Nucleolar organizer regions in smears of pleural effusion.

Agyrophil staining was applied to nucleolar organizer regions (NOR) to differentiate cells of adenocarcinoma and histiomesotheliosis in pleural effusion. The smears were either nuclearly unstained, but cytoplasmically counterstained by Papanicolaou method or Papanicolaou-destained before agyrophil staining of nucleolar organizer regions (AgNOR). The purposes of this study were to assess the feasibility and usefulness of AgNOR staining in diagnostic cytology and to try to set up a procedure that could be used on prestained smears for retrospective study. All smears showed good background and cellular outline. The distribution of NOR was either intranuclearly or in the nucleoplasm diffusely. In previously nuclearly unstained smears, NOR showed granular to powder-like appearance. The mean number of NOR in adenocarcinoma (38.4 +/- 12.5) was significantly higher than that in histiomesotheliosis (15.6 +/- 2.9). In Papanicolaou-destained smears, the NOR showed confluent dots. The mean number of NOR was much lower as compared to that of previously nuclearly unstained smears. Furthermore, the mean number of NOR in adenocarcinoma (3.6 +/- 1.4) showed no significant difference with that of histiomesotheliosis (2.7 +/- 0.8). In conclusion, AgNOR staining is one of the methods to differentiate benign from malignant cells, but not in Papanicolaou-destained smears.

Variation in the distribution of silver-staining nucleolar organizer regions on the chromosomes of the wild mouse, Mus musculus.

A silver staining method was used to analyze the distribution of nucleolar organizer regions (Ag-NORs) on chromosomes of 45 wild mice (Mus musculus). The four subspecies represented were M. m. musculus, M. m. molossinus, M. m. castaneus, and M. m. bactrianus. Ag-NORs were observed near the centromeric regions of 11 chromosomes (4, 8, 9, 10, 11, 12, 15, 16, 17, 18, and 19), indicating a preponderance of Ag-NORs on smaller chromosomes. The first five loci have not been observed previously. It is suggested that a correlation may exist between the specific features of mouse Ag-NORs and the events involved in intra- and interchromosomal homogenization of rDNA.

Nucleolar organizer regions in normal skeletal muscle and benign and malignant rhabdomyoblastic tumors.

The silver staining of interphase nucleolar organizer regions (NORs) has been shown to have an important application in diagnostic histopathology for distinguishing some benign from malignant conditions. In this study, normal fetal and adult skeletal muscles and tissue from fetal and adult rhabdomyomas as well as rhabdomyosarcomas were stained with the silver method for NORs. The morphologic distribution of NORs in rhabdomyosarcomas was found to be very different from that in normal skeletal muscles. In addition, cases of rhabdomyoma were easily differentiated from rhabdomyosarcomas. Statistical analysis of data, from all cases, regarding the diameter of NORs and number per nucleus confirmed these observations.

Interphasic nucleolar organizer region distribution as a diagnostic parameter to differentiate benign from malignant epithelial tumors of human intestine.

The distribution of the interphasic nucleolar organizer regions (NORs) has been investigated in five hyperplastic polyps, five adenomatous polyps and fifteen colonic adenocarcinomas. The study was performed using electron microscopy and paraffin-embedded sections stained for Ag-NOR proteins. Malignant tumor cells were characterized by a large number of NORs which were small in size and showed a scattered distribution. Nuclei of both types of polyp had only a small number of large-sized NORs in a clustered distribution. In two adenomatous polyps, cells were also observed with an NOR distribution pattern intermediate between that of frankly benign and malignant lesions.

The chromosomes of two Drosophila races: D. nasuta nasuta and D. nasuta albomicans III. Localization of nucleolar organizer regions

In the two Drosophila races D. n. nasuta and D. n. albomicans the nucleolar-organizer regions (NORs) have been localized on metaphase chromosomes by a combined acid treatment and silver-staining technique. In both Drosophila races one NOR is present on the heterochromatic Y chromosomes and another on the microchromosomes. Such a NOR distribution has not yet been reported in Drosophila. It is suggested that this distribution has evolved from an original type with NORs on the X and Y chromosomes.