Chromosomal Nucleolar Organizer Research Articles

Karyological study of some cultivated and wild stocks of pearl millet from Africa (Pennisetum typhoidesStapf et Hubb. andP. violaceum(Lam.) L. Rich.)

SUMMARYFour pearl millet genotypes originating from different African geographic areas (Ligui, 23 DB, Thiotande and Pennisetum violaceum) have been studied. The karyotypes of these genotypes are compared on a statistical basis. The karyotype is generally symmetrical with six pairs of metacentric and one pair of submetacentric satellited chromosomes. The heterochromatic B chromosomes occur only in P. violaceum. The karyotypic polymorphism, especially on nucleolar organizer (NOR) chromosome pair is also found. The structure and morphology of the chromosomes bearing the nucleolar organizer in pearl-millet is discussed.

Chromosomal nor Karyotypes and Genome Sizes in Dionda (Osteichthyes: Cyprinidae) from Texas and New Mexico

Chromosome numbers, chromosomal nucleolar organizer egion (NOR) phenotypes, and genome sizes (DNA contents) were documented for all nominal members of the North American cyprinid genus Dionda inhabiting Texas and New Mexico. All examined taxa, including four members of the Dionda episcopa complex (D. episcopa, D. argentosa, D. serena, and an undescribed species inhabiting the Colorado and Guadalupe river drainages in Texas) and D. diaboli, possessed 2n = 50 chromosomes, with a single pair of NOR-bearing chromosomes. Ineach, the chromosomal NOR was located terminally on the short arm of a small-sized acrocentric chromosome. All of the NOR chromosomes appeared to be homologous in trypsin G-banding pattern. Mean genome sizes ranged from 1.94 picograms (pg) of DNA in D. serena from the Nueces River to 2.09 pg of DNA in D. argentosa from Baker's Crossing in the Devils River. Divergence in genome size among nearly all of the samples of Dionda was less than that maximally observed, on average, between individuals within populations of most North American fishes. Collectively, the chromosomal NOR and genome size data suggest that the taxonomic status of Dionda inhabiting Texas and New Mexico may warrant further inves-

Cytogenetic Studies in North American Minnows (Cyprinidae). XX. Chromosomal NOR Variation in the Genus Luxilus

Chromosomal nucleolus organizer region (NOR) phenotypes are documented for all extant taxa of the North American cyprinid genus Luxilus. All nine species, including two subspecies of L. chrysocephalus (L. c. chrysocephalus and L. c. isolepis), possess 2n = 50 chromosomes. Five species and one population of L. c. isolepis from the Blue River in Oklahoma possess a single pair of NORbearing chromosomes. These included L. cerasinus and L. c. isolepis from Oklahoma (NOR phenotype C), L. zonistius (NOR phenotype D,), and all three species (L. cardinalis, L. pilsbryi, and L. zonatus) of the L. zonatus group (NOR phenotype Dj). Four taxa (L. albeolus, L. coccogenis, L. c. chrysocephalus, and L. cornutus) and populations of L. c. isolepis from Alabama, Mississippi, and Louisiana possess two pairs of NOR-bearing chromosomes (NOR phenotype C, D,). A serial banding procedure (Z-banding) was used to test homology of C, D,, and D, NOR chromosomes. The NOR chromosome data support monophyly of the L. cornutus group (L. albeolus, both subspecies of L. chrysocephalus, and L. cornutus) and L. coccogenis. Assuming the L. coccogenis group (L. coccogenis and L. zonistius) is monophyletic, as suggested by morphological, allozymic, and mtDNA data, the chromosomal data support the hypothesis that the L. coccogenis and L. cornutus groups are sister taxa and that L. cerasinus is sister to the L. coccogenis groupL. cornutus group clade. Because the D, NOR chromosome of all three species of the L. zonatus group does not occur elsewhere in Luxilus, there is no chromosomal evidence for a phyletic relationship between the L. zonatus group and any other species in Luxilus. The hypothesis that the L. coccogenis group is sister to the L. cornutus group suggests that the missing species of Luxilus in the Ohio River-northern Atlantic slope drainages may have been a member (or ancestor) of the L. cornutus group.

Cytogenetic Studies in North American Minnows (Cyprinidae). XXVI. Chromosomal NOR phenotypes of 21 species from the Western United States.

Karyotypes and chromosomal nucleolus organizer region or NOR phenotypes of 19 described and two undescribed species of western North American cyprinids are documented. All 21 species examined possessed 2N=50 chromosomes and at least two pair of NOR-bearing chromosomes. The high incidence of multiple NOR chromosomes among western cyprinids is unusual. One pair of A NOR chromosomes was found in all 21 species, and 17 species possessed a second pair of A NOR chromosomes. An AA NOR state was hypothesized to represent a chromosomal synapomorphy uniting western cyprinids (including the genus Richardsonius) into a monophyletic assemblage. Within this clade, a transition from an A NOR to a D NOR was hypothesized to represent a chromosomal synapomorphy uniting three speices of the subgenus Gila, and an addition of an F NOR was hypothesized to represent a chromosomal synapomorphy uniting two species of the genus Rhinichthys. Chromosomal NORs in western cyprinids appear conserved relative to eastern cyprinids and may be the result of (i) a process of karyotypic canalization, and/or (ii) character state reversal in, or introgressive hybridization among, western cyprinid genera.

Visualization of Ribosomal Gene Activity in Oogenesis of Reticulitermes Iucifugus(Isoptera: Rhinotermitidae) Revealed by Silver Staining.

The Ag-pattern of amplified nucleolar material in various stages of R. lucifugus oogenesis has been followed. At zygotene a nucleolar mass is associated with chromosomal nucleolar organizer regions. At pachytene small brown extra nucleoli are interspersed among the bivalents. At early diplotene the microuncleoli fuse into larger nucleoli. During the late stage of oogenesis large masses of silver stainable material (ribonucleoprotein aggregates) are released in the cytoplasm.

Cytogenetic studies in North American minnows (Cyprinidae). XXII. Chromosomal nucleolar organizer regions in the genus Pimephales

Chromosomal nucleolar organizer region (NOR) phenotypes are documented for all four extant species in the North American cyprinid fish genus Pimephales. All four species (P. notatus, P. promelas, P. tenellus, and P. vigilax) possess 2n = 50 chromosomes and a pair of NOR-bearing chromosomes with the NOR situated terminally on the short arm of a medium-sized to large submetacentric chromosome (NOR phenotype C). Trypsin G-banding demonstrated that the C NOR chromosome in all four species is homologous. Two of the species (P. tenellus and P. promelas) also possess a C′ NOR chromosome, which is defined as an NOR situated terminally on the short arm of a large submetacentric chromosome that is also the largest chromosome in the complement. The C′ NOR chromosome occurs infrequently in P. promelas, being found in only 8% or so of all metaphases examined. Trypsin G-banding demonstrated that the C′ NOR chromosomes in the two Pimephales species are homologous to one another and to the C′ NOR chromosomes found in the cyprinid genus Cyprinella. A presumed derivative of the C′ NOR chromosome occurs in the monotypic cyprinid genus Opsopoeodus. The NOR chromosomal data support monophyly of the four extant species of Pimephales, and further suggest that the genus Pimephales belongs in a monophyletic assemblage with, among others, the cyprinid genera Cyprinella and Opsopoeodus. The data do not support the previous hypothesis that Pimephales is a basal clade outside of a larger assemblage of "Notropis"-like, shiners.

Formation of Nucleolar Polymorphisms in Trisomic Chickens and Subsequent Microevolution of rRNA Gene Clusters in Diploids

Variations in nucleolar size are common in animals and man, yet the basis and significance of this variation are not well understood. In this report, we describe the generation de novo of individuals that express nucleolar size variations (polymorphisms) and the underlying basis for this phenotype in a vertebrate animal system (Gallus domesticus). Individuals that express nucleolar size polymorphisms were produced from mating chickens trisomic for the nucleolar organizer (NO) chromosome; 10%-18% of progeny demonstrated nucleolar polymorphisms. These progeny were incorporated into a diploid genetic line in which the polymorphic trait was observed to segregate in Mendelian fashion. An even more dramatic nucleolar size polymorphism (one macro- plus one micronucleolus) evolved in one diploid family over the course of only two generations. These individuals were used to ascertain that the polymorphic-nucleoli phenotype was expressed in tissues derived from the three primary embryonic cell layers in embryos and neonates. Image analysis was conducted on cells of these birds to quantitate the size differences between macro- and micronucleoli (5 mu2 versus 1 mu2, respectively). Finally, these birds were studied with the technique of in situ hybridization, which showed that gene number differences between homologous NO chromosomes (i.e., heterozygosity for rRNA gene copy number), underlies the polymorphic-nucleoli phenotype. Thus, the chicken emerges as an experimental system through which heterozygosity for the rRNA gene copy number can be induced, easily identified, transmitted, and expressed in all somatic tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of nucleolus organizer chromosomes in goat (Capra hircus)

SUMMARYSequential RBA/Ag-NOR- and GBG/Ag-NOR-banding techniques were employed on a total of fourteen Saanen and Maltese goats (Capra hircus, 2n = 60) reared in Southern Italy in order to identify which chromosomes carry nucleolus organizer regions (NORs). The procedure allowed the location of NORs at the telomeres of chromosomes 2, 3, 5, 6 and 28 of G-and R-banded goat karyotypes, which were arranged according to the ISCNDA (1989). The indirect comparison of goat, cattle and river buffalo nucleolar organizer (NO) chromosomes revealed the following common homologous NO-chromosomes: (a) 2, 3 and 6 between goat and cattle; (b) 6 (8) and 28 (4p) between goat and river buffalo; (c) 6 (8) among the three species.

1R chromosome nucleolus organizer region activation by 5-azacytidine in wheat × rye hybrids

Nucleolar activity was studied in several lines of Triticum aestivum cv. Chinese Spring, Triticum turgidum cv. Durum, and F1 hybrids from euploid and aneuploid lines of T. aestivum and Secale cereale cv. Centeio do Alto, in cells from root tips of seeds germinated in water or in 5-azacytidine. 5-Azacytidine, an analog of cytidine modified in the 5 position of the pyrimidine ring, inhibits DNA methylation. By using silver staining to determine the number of nucleolus organizer regions and the average number of nucleoli per root-tip cell from seeds germinated in both situations, it became apparent that the presence of 5-azacytidine during germination allowed for the expression of the nucleolus organizer region locus belonging to the rye genome, in contrast to the usual observed cytological absence of the rye nucleolus organizer region in wheat–rye hybrids. It is suggested that wheat nucleolar dominance in wheat–rye hybrids is mainly a consequence of methylation of rRNA genes or its regulators located on the 1R chromosome of rye.Key words: 1R nucleolar organizer, wheat–rye hybrids, methylation, Ag-NOR.

Relative abundance of various rDNA repeat types in polytene nuclei of Drosophila melanogaster

The relative abundance of the five predominant X chromosome nucleolus organizer repeat types was determined in polytene nuclei. Previous studies showed that the major type I insert containing class of repeats was disproportionately underreplicated when compared with the insert-free class of repeats in these nuclei. Our results demonstrate that this disproportionate underreplication also occurs for both the minor type I and type II insert containing repeats. There was not an exclusive polytenization of the insert-free repeats for this wild-type X nucleolus organizer region. A repeat type lacking either insert type and having an unusually long nonstrancribed spacer was identified and found to be preferentially replicated in polytene nuclei. Preliminary mapping studies indicate that this class of repeats has a unique location, in the distal portion of either the X nucleolus organizer region or the centric heterochromatin. Their similarity to the common insert-free repeats includes preferential polytenization and generalized DNase I sensitivity, which suggests that they are transcriptionally active.

Cytological examination of three cultivars of garlic (Allium sativumL.) by C-banding and flow cytometry

Abstract C-banded karyotypes were prepared for three of the more important garlic (Allium sativum L.) cultivars grown in New Zealand, ‘California Early’, ‘California Late’, and ‘Red Garlic’. The cultivars all have unique banding patterns with the largest bands at the sites of secondary constrictions. Further bands were located in terminal positions on different numbers of chromosomes in the three cultivars. A limited number of bands were seen in interstitial positions, especially on the nucleolar organiser (NOR) chromosomes. Centromeric bands were entirely absent. Flow cytometry was used to measure nuclear DNA amounts which were found to be the same in the three cultivars.

Cytogenetic studies in North American minnows(Cyprinidae). XVIII. Chromosomal NOR variation among eight species.

The karyotypes and chromosomal nucleolus organizer region or NOR phenotypes of eight species of North American cyprinid fishes are documented. All eight species possessed 2n=50 chromosomes. Four species (Cyprinella formosa, Cyprinella gibbsi, Notropis boops, and Notropis dorsalis) possessed only a single pair of NOR-bearing chromosomes, whereas four species (Notropis petersoni, Notropis sabinae, Phenacobius mirabilis, and Semotilus atromaculatus) possessed multiple NORs, i. e., more than one pair. The phylogenetic implications of the chromosomal NOR data in the eight species are discussed relative to current concepts of North American cyprinid systematics based largely on morphological data. A phylogenetic hypothesis based on chromosomal NOR and other data is presented for 11 species of the cyprinid genus Cyprinella, and our previous hypothesis that a single pair of NOR chromosomes is the plesiomorphic NOR state for a large eastern North American cyprinid lineage is questioned.

Differential decondensation of mitotic chromosomes during hypotonic treatment of living cells as a possible cause of G-banding: an ultrastructural study.

The chromosomal ultrastructure of Chinese hamster cells treated with 0.075 M KCl - a solution ordinarily used for making preparations of spread chromosomes - was studied. The hypotonic treatment was shown to result in differential decondensation of chromosomes which consists in the uneven distribution of deoxyribonucleoprotein (DNP) fibrils along chromatids. Fixation of cells with methanol acetic acid causes an abrupt restructuring of chromosomes. However, the DNP preserves its uneven distribution along chromatids. As seen on ultra-thin sections of marker nucleolus organizer chromosomes, the densely packed regions may correspond to G-bands detected in the selfsame chromosomes by standard methods of differential staining. The results suggest that the capacity of chromosomes for differential staining is based on the different resistance of G- and R-bands to the decondensing action of hypotonic solutions on living cells.

Three-dimensional chromosome arrangement of Crepis capillaris in mitotic prophase and anaphase as studied by confocal scanning laser microscopy.

To estimate the extent of ordering of chromosomes, confocal scanning laser microscopy was used to make three-dimensional images from optical sections. For Crepis capillaris, which has 2n = 6 easily recognizable chromosomes, a statistically significant sample of 75 Feulgen-stained root tip anaphases was analysed. A comparison of the observed chromosome ordering and the expected random distribution showed a significant surplus of one of the arrangements with a juxtaposition of the two chromosomes with a nucleolus organizer region. Two of the arrangements with these chromosomes in opposite positions were never observed in our material. Another analysis of 30 mithramycin A-stained prophases and 30 meta- and anaphases showed partly different patterns of non-random chromosome distribution in the two stages of mitosis. A preference for an association of the homologues was observed for all pairs of chromosomes in prophase cells, whereas in meta- and anaphase the association only persisted for the nucleolus organizer chromosomes. This indicates that there may be some relocation of the chromosome positions during the transition from prophase to metaphase. In meta- and anaphase one of the arrangements with juxtaposed NOR chromosomes was preferred, i.e. the ordering in which chromosomes 1 and 3 occupied alternate positions. Probably, the nucleolus is an important factor in producing a non-random distribution, but there could be other factors that influence chromosome ordering as well. A comparison of the anaphase chromosome ordering in C. capillaris plants from very different localities, indicated that the observed non-random distribution was independent of the origin of the material. Existing models of chromosome disposition are not sufficient to explain the observed non-random chromosome ordering in C. capillaris.

Patterns of Chromosomal Nucleolar Organizer Region (NOR) Variation in Fishes of the Genus Salvelinus

Description de la localisation chromosomique des NOR chez 2 especes S. malma et S. confluentus et presentation d'une hypothese phylogenetique concernant les relations entre ces especes

Relationship between the number and function of human ribosomal genes

The relative number of ribosomal RNA genes of the acrocentric chromosomes in one individual was measured by counting grains after in situ hybridization of 3H-labeled human 18S rDNA to fixed metaphase chromosomes. The relative amount of ribosomal RNA gene activity of each of the same chromosomes was estimated by determining the frequency with which the chromosome's nucleolus organizer region (NOR) was silver stained, the size of the silver-stained region, and how often the chromosome was found in satellite association. Results were similar in phytohemagglutinin-stimulated T-lymphocytes, Epstein-Barr virus transformed lymphoblasts, and fibroblasts. One chromosome 21 had few gene copies and low activity. One chromosome 22 had many gene copies but low activity. Both chromosomes 14 had few gene copies but high activity. The level of expression that can be achieved by rRNA gene clusters can, therefore, be determined by factors other than the number of gene copies.

Nucleolar behavior in pollen mother cells in the pigeonpea

Reports on the number of satellite chromosomes in the karyotype of Cajanus cajan are controversial, with the number varying from zero to two. Expression of nucleolar organizer chromosomes during melosis (prophase-I, telophase-I and telophase-II) is used as an index for the number of nucleolar organizers and conclusive evidence is provided for the presence of two nucleolar organizer chromosomes in Cajanus and also its related species in the genus Atylosia. Nucleolar number in an autotetraplold of Caianus confirmed the evidence from the diploid Cajanus for two nucleolar organizer chromosomes. Variation In the nucleolar size suggests that the two nucleolar organizer chromosomes differ in their activity.

Inhibition of nucleolar reformation after microinjection of antibodies to RNA polymerase I into mitotic cells.

The formation of daughter nuclei and the reformation of nucleolar structures was studied after microinjection of antibodies to RNA polymerase I into dividing cultured cells (PtK2). The fate of several nucleolar proteins representing the three main structural subcomponents of the nucleolus was examined by immunofluorescence and electron microscopy. The results show that the RNA polymerase I antibodies do not interfere with normal mitotic progression or the early steps of nucleologenesis, i.e., the aggregation of nucleolar material into prenucleolar bodies. However, they inhibit the telophasic coalescence of the prenucleolar bodies into the chromosomal nucleolar organizer regions, thus preventing the formation of new nucleoli. These prenucleolar bodies show a fibrillar organization that also compositionally resembles the dense fibrillar component of interphase nucleoli. We conclude that during normal nucleologenesis the dense fibrillar component forms from preformed entities around nucleolar organizer regions, and that this association seems to be dependent on the presence of an active form of RNA polymerase I.

On the position of nucleolus organizer regions (NORs) in interphase nuclei: Studies with a new, non-autoradiographic in situ hybridization method

The distribution of 18S and 28S ribosomal RNA (rRNA), i.e. the chromosomal nucleolus organizer regions (NORs) was visualized in interphases and metaphases of non-stimulated and phytohemagglutinin (PHA)-stimulated human lymphocytes with a recently developed non-autoradiographic in situ hybridization method. This procedure involves mercurated RNA as a probe and a sulfhydryl-trinitrophenyl-mercury binding ligand and FITC-labelled antibodies as detection system. Silver staining was used to visualize nucleoli in interphase. In the secondary constriction of all ten acrocentric chromosomes, varying amounts of rDNA were detected. In the interphase nuclei of most of the non-stimulated human lymphocytes, only one small nucleolus could be seen. The in situ hybridization, however, revealed several agglomerations of rDNA scattered over the whole nuclear area, clearly outnumbering the number of nucleoli in these cells. This means that not all of the NORs are transcriptionally active in non-stimulated lymphocytes and that these inactive NORs lie at a distinct distance from the actives ones. With PHA stimulation (transforming the small lymphocytes from peripheral blood into large, lymphoblast-like cells) the number of nucleoli increased slightly, whereas the number of separable rDNA spots decreased. This means that in the course of PHA-induced cellular activation, formerly inactive NORs become transcriptionally active and tend to associate with one another. This indicates the occurrence of movements of the NORs within the nucleus, depending on their transcriptional activity.

Cytogenetic studies in North American minnows (Cyprinidae). XII. Patterns of chromosomal nucleolus organizer region variation among 14 species

The chromosomal nucleolus organizer region (NOR) phenotypes of eight species of North American cyprinid fish are documented. This brings the total number of cyprinid species examined for chromosomal NORs to 14. At least 10 different NOR chromosome phenotypes are identifiable among the 14 species. These interspecific variations include differences in the (haploid) number of chromosomal NORs, the chromosomal location(s) of the NORs, and the type(s) of chromosomes upon which the NOR is located. Intraspecific variations or heteromorphisms of NOR chromosomes also occur, but are of a qualitatively different nature than the NOR variants observed between species. Arrangement of the interspecies NOR differences into phylogenetic hypotheses yields results which are not discordant with present concepts of North American cyprinid taxonomy, and in fact support the hypothesis of a close relationship between the cyprinid genera Notropis and Pimephales. These data suggest that NOR chromosome phenotypes will be useful in resolving problems in cyprinid systematics. The data also show that at least one or more chromosomal changes involving the NOR separate most of the species examined, and that at least nine different chromosomal rearrangements have occurred since the 14 species last shared a common ancestor. This suggests that chromosomal changes in cyprinids have been much more frequent than previously thought.