Cytological evidence on the ability of the nucleolus organizing regions to assemble pre-existing nucleolar material

The treatment of Vicia faba root tips with 5-azacytidine caused unequal allotment of the chromosomes; after one cell cycle, a pair of daughter nuclei was produced, one of which carried the nucleolus organizing regions (NORs) and the other of which lacked them. The pre-existing nucleolar material brought into the NOR-carrying daughter nucleus by the chromosomes disappeared concurrently with the appearance of the new nucleoli, whereas in another daughter nucleus without the NOR a number of small nucleolus-like bodies became visible at random positions. These findings suggest that in addition to ribosomal RNA synthesis the NOR has another role in cells; to stimulate the pre-existing nucleolar material to assemble at the NOR itself.     

Detection of nucleolus organizer regions (NOR) in the chromosomes of the domestic pig (Sus scrofa domestica L.)

Summary In the domestic pig (Sus scrofa domestica L.) nucleolar organizer regions (NOR) were detected by a combined silver-Giemsa method (Ag-G). The main sites of NORs are the secondary constrictions of chromosomes 8 and 10. Sometimes an additional NOR was observed near the centromere of 1 homologue of chromosome 11. Associations of NORs were seen only between chromosomes 10 and at a very low frequency.     

Detection of nucleolus organizer regions (NOR) in the chromosomes of the domestic pig (Sus scrofa domestica L.)

In the domestic pig (Sus scrofa domestica L.) nucleolar organizer regions (NOR) were detected by a combined silver-Giemsa method (Ag-G). The main sites of NORs are the secondary constrictions of chromosomes 8 and 10. Sometimes an additional NOR was observed near the centromere of 1 homologue of chromosome 11. Association of NORs were seen only between chromosomes 10 and at a very low frequency.     

The silver-staining technique—a tool for characterizing lymphocyte populations in mammalian peripheral blood

Summary Nucleolus organizer regions (NORs) of the peripheral blood lymphocytes (PBL) of 9 mammalian species were analyzed by means of a silver-staining procedure. Species-specific NOR patterns were demonstrated. The number of NOR chromosomes was positively correlated with the nucleolar coefficient, and negatively correlated with the relative frequencies of uninucleolar cells in PBL interphase.Acknowledgment. The authors thank Professor Dr E. Groll-Knapp, of the Institute of Environmental Hygiene at the University of Vienna, for statistically evaluating the data provided.     

Position of the nucleolus within the nuclei of pachytene spermatocytes of Dromiciops australis and Marmosa elegans (Didelphoidea-Marsupialia).

The location of the nucleoli within the nuclei of pachytene spermatocytes, and their relation with the position of the nucleolar organizer region (NOR) was studied. It appears that a terminal NOR determines a peripheral location of the nucleolus, due to the position of the NOR over the synaptonemal complex and to the attachment of the nucleolar chromosome telomeres at the nuclear membrane.     

Chromosome arrangement throughout mitosis and interphase inAllium sativum (Liliaceae)

Summary Allium sativum (garlic) root-tip chromosomes were subjected to a C-banding procedure. In addition to the nucleolar bands reported previously in this species, bands which are telomeric or close to the telomeres have been detected in some pairs. This has allowed us to analyze the arrangement of chromosomes during interphase.     

Variable positions of nucleolus organizer regions in Bovidae

Summary Silver NOR staining has been applied to cattle (Bos taurus L.), goat (Capra hircus L.) and sheep (Ovis aries L.) chromosomes. The sites of silver NORs showed variation within the family Bovidae probably due to a reciprocal translocation event.     

Distribuzione di fosfatasi alcaline in gonadi di Crostacei isopodi in rapporto al ciclo degli acidi nucleici

Summary The distribution of alkaline phosphatases has been studied in male and female gonads of some isopod crustaceans by means of Gomori's reaction.Monophosphatases are found on all Feulgen-positive nuclear structures, in the nucleolus and in the cytoplasm of young oocytes. They disappear from the cytoplasm in auxocytosis, during yolk formation, although they persist in the germinal vesicle. The authors think that the cytoplasmic localization is coincident with ribonucleic acid distribution.From the experiments related in the following note, nucleolar phosphatases appear to be in some way different from the nuclear (sensu stricto) and cytoplasmic phosphatases.Diphosphatases do not follow so closely the nucleic acid localization. They are absent from cytoplasm; in the nucleolus they are not distributed uniformly but show characteristic structure; in the nucleus they are not localized in the chromosomes but homogeneously diffused.     

The karyotypes of the Corsican and Sardinian mountain salamanders,Euproctus montanus andE. platycephalus (Urodela: Salamandridae)

Summary The chromosomes ofEuproctus montanus andE. platycephalus were studied by means of the C-banding method and the AS-SAT technique which are useful for identifying the single pairs of the complement and for recognizing nucleolar organizer regions. According to the morpho-structural characteristics shown by the specific karyotypes, it has been possible to draw some cytotaxonomic deductions concerning the karyological evolution within the insular group.This work was supported by grant CT 76.01271.04/115.3822 from C.N.R., Rome.     

C-band differentiation between the chromosomes of two subspecies of the chironomid midgeChironomus thummi

Summary The metaphase chromosomes ofChironomus th. thummi contain approximately 17% more pericentric C-band heterochromatin than the chromosomes ofChironomus th. piger with 11% heterochromatin. InCh. th. thummi, the proportion of heterochromatin appeared to be much larger in metaphase chromosomes than in polytene chromosomes. This discrepancy is interpreted as being due to the specific chromosome organization and not as the result of an underreplication of heterochromatin during polytenization.     

Supernumerary chromosomes inDrosophila nasuta albomicana

Summary Supernumerary chromosomes have been detected in the karyotype ofD.n. albomicana. Their number varies from one to three. They are the smallest elements in the karyotype. Karyotypes ofD.n. albomicana with and without supernumerary chromosomes have been presented.     

Telomere dynamics unique to meiotic prophase: formation and significance of the bouquet

Telomeres carry out conserved and possibly ancient functions in meiosis. During the specialized prophase of meiosis I, meiotic prophase, telomeres cluster on the nuclear envelope and move the diploid genetic material around within the nucleus so that homologous chromosomes can align two by two and efficiently recombine with precision. This recombination is in turn required for proper segregation of the homologs into viable haploid daughter cells. The meiosis-specific telomere clustering on the nuclear envelope defines the bouquet stage, so named for its resemblance to the stems from a bouquet of cut flowers. Here, a comparative analysis of the literature on meiotic telomeres from a variety of different species illustrates that the bouquet is nearly universal among life cycles with sexual reproduction. The bouquet has been well documented for over 100 years, but our understanding of how it forms and how it functions has only recently begun to increase. Early and recent observations document the timing and provide clues about the functional significance of these striking telomere movements.     

Constitutive heterochromatin and nucleolus organizer region in the knifefish,Apteronotus albifrons (Pisces,Apteronotidae)

Summary The C-banding and silver staining of the chromosomes of the knifefishApteronotus albifrons (2n=24), demonstrated the presence of constitutive heterochromatin in the centromeric region of every chromosome, except pair 4, where the entire long arm was darkly stained, the silver stain positive nucleolus organizer region (NOR) being embedded in it.The authors are grateful to Dr Sen Pathak (University of Texas System Cancer Center at Houston, Texas, USA) and Dr Yatiyo Yassuda (Universidade de São Paulo, São Paulo, Brasil) for their suggestions. This study was supported in part by grants of the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq).     

Heterochromatin characterization and distribution in the chromosomes of two populations ofIdotea baltica basteri Audouin, 1826 (Isopoda,Valvifera)

Two mediterranean populations ofIdotea baltica basteri from Messina and Naples showed a set of chromosomes composed by 58 all-biarmed chromosomes. The heterochromatin was located in the pericentromeric region of the chromosomes, and its composition appeared heterogeneous. In fact, not all the homologs showed heterochromatin resistant to digestion with three restriction enzymes (Alu I, Hae III and Sau 3A). Moreover, the two populations showed polymorphism in a band of G+C-rich telomeric heterochromatin, which was present only in the population from Messina. It is hypothesized that chromosomal polymorphism might reflect the geographical isolation of the two populations. It is also suggested that a process of diversification is taking place.     

Chromosome-breaking activity of extracts of the mushroomPaxillus involutus Fries ex Batsch

Summary Dry and presoaked seeds ofNigella damascena were treated with aqueous extracts of the mushroomPaxillus involutus. At the first mitosis after the onset of germination, metaphase chromosomes showed damage independent of the origin of the mushrooms. The damaging substance(s) is (are) thermostable. Except a few achromatic gaps, all the lesions observed are of the chromosome type, i.e. are induced at the pre-synthetic G1 stage.     

Chromatin structure contribution to the synaptonemal complex formation

Meiosis is a key cellular and molecular process for sexual reproduction contributing to the genetic variability of organisms. This process takes place after DNA replication and consists in a double cellular division, giving rise to four haploid daughter cells or gametes. Meiotic recombination between homologous chromosomes, in the meiotic prophase I, is mediated by a tripartite structure named Synaptonemal Complex (SC). The SC is a peptidic scaffold in which the chromatin of homologous chromosomes is organized during the pachytene stage, holding chromosomes together until the meiotic recombination and genetic exchange have taken place. The role of chromatin structure in formation of the SC and the meiotic recombination at meiotic prophase I remain largely unknown. In this review we address the epigenome contribution to the SC formation at meiotic prophase I, with particular attention on the chromatin structure modifications occurring during the sub-stages of meiotic prophase I. Received 18 September 2008; received after revision 10 October 2008; accepted 24 October 2008     

Fine structure of differentiated chromosome segments during the meiosis of pollen mother cells of Allium cepa

Summary Differentiated chromosome segments were observed during studies of pollen mother cells of A. cepa during the first meiotic division. Their structure is like those of the nucleolar organizing region (NOR) described in A. cepa microspores. It is suggested that these differentiated chromosome segments correspond to the secondary constrictions seen under the optical microscope.     

A new chromosome number forBombina (Anura,Discoglossidae)

Summary The karyotype of a primitive discoglossid anuran,Bombina maxima, native to southwestern China, has 2n=28 chromosomes with 6 large and 8 small bi-armed homologous pairs. This is a higher chromosome number than described for otherBombina species, all of which have 2n=24.     

Genetic basis of some morphological differences between temperate and equatorial populations ofDrosophila melanogaster

The genetic basis of three morphological traits (ovariole number, sternopleural bristle number and wing length) ofDrosophila melanogaster has been investigated in natural populations that show great differences in these traits, i. e. Bordeaux (France) and Loua (Congo). F1 and F2 crosses, and chromosome substitutions between these two populations, were analysed. Maternal and/or X chromosome effects were found for sternopleural bristle number and wing length. For all traits, significant effects from each of the three chromosomes were found, but in general only one or two chromosomes had a major effect. Moreover, in all cases significant interactions between chromosomes were observed, suggesting the existence of epistatic effects. Our results are discussed and compared to those obtained from the analysis of selected laboratory strains.