Simultaneous activity of nucleolus organizer regions of human and Chinese hamster chromosomes in somatic cell hybrids

In an interspecific human-Chinese hamster hybrid that retains 13 and 85.6% of the chromosomes of each parental complement, activity of nucleolus-organizing regions (NOR) of both type chromosomes is observed in 18.9% of the cells. Interspecific chromosomal associations are also noted. Unlike the parental lines of Chinese hamster cells, the hybrids show the associations of the NOR of Chinese hamster chromosomes. In hybrid cells, there occurs partial suppression of NOR activity in human and Chinese hamster chromosomes, while the NOR of the 3d chromosome of the Chinese hamster is completely suppressed.     

Sex ratio in hybrid mice CBA X C57BL

Sex ratio and postimplantation mortality were studied in (CBAXC57BL)F1, CBA and C57BL mouse embryos. It has been shown that female fetuses are predominant in the progeny of hybrid mice. In CBA and C57BL mice the sex distribution was 1 : 1. The disorder in the balanced sex ratio in the progeny of hybrid mice confirms a conclusion on the effect of the mouse genetic features on the sex distribution in embryos. Equal sex ratio in CBA and C57BL mice indicates the absence of selective mortality in the embryos of either sex during embryogenesis.     

Frequency of Ag-stained nucleolus organizer regions in the chromosomes of cattle

Sequential Ag NOR/G-band studies were performed on the chromosomes of 33 Austrian Al bulls. The mean number of Ag-NORs per bull karyotype was 6.06. The distribution of Ag-NORs was found to be characteristic for each individual.     

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     

Behavior of the nucleolus organizer regions of the chromosomes in polykaryocytes consisting of micronuclei

The nucleolar organizer regions (NORs) of Chinese hamster chromosomes (clone 237, cell line BIId-ii-FAF28) were studied in mononuclear cells and polykaryocytes induced with colcemid. The chromosomes with NORs were marked as 1, 2, 3, 4. The activity of NORs in mononuclear cells was higher in chromosomes 1, 2, 3. The associations of NORs were observed between chromosomes I and 2 (3% of all metaphases). In polykaryocytes the chromosomal pairs 1, 2, 3 showed different NOR activity in different metaphases. The associations of NORs in pairs of chromosome I were found in 51.3% of cases. The associations of NORs in pairs of chromosome 2 were observed in 7.5% of cases. This method may be used for the estimation of association potency of NORs in chromosomes.     

Cytological analysis of radiation-induced DNA amplification in C57BL/6 mice

Inbred mouse strain C57BL/6 pre-treated with or without the drug with suspected anticancer activity, DADH (N, N'-Diacetyl-1, 6-Diaminohexane) by daily feeding for five consecutive days to a total dose of 1 mmol of the drug in aqueous solution, were exposed to an acute dose of 1 Gy gamma radiation. Appropriate controls without radiation were maintained both for water and DADH-fed groups of animals. At 18 and 36 h post-irradiation the animals from all four groups (designated as A to D with each group having six animals) were sacrificed and their bone marrows were cultured for chromosomal analysis. Special emphasis was put on the estimation of the frequency of occurrence of extra chromosomal elements, such as minutes, single or double (DMS) as a possible assay for radiation-induced DNA amplification (presumably representing the proliferation specified genes(?) causing initiation of a very early tumourigenesis event). Gamma irradiation alone yielded the highest frequency of such minute chromosomal structures concerned (DMS), which was significantly reduced by DADH pre-treatment. The preliminary cytological data are discussed in the light of current information on DNA amplification pertaining to carcinogenic induction.     

Dynamic of nucleolus organizer regions and karyotype evolution in Indian pygmy field mice

Ag-NOR staining and fluorescence in situ hybridization with rDNA probes showed an unusually high number of NORs in the Indian pygmy field mice, Mus booduga and the M. terricolor complex. The chromosomal location of the NORs was also altered in terricolor, they were shifted from the proximal regions of the long arms to the tips of the perceptible heterochromatic short arms of the acrocentric autosomes. The results suggested dispersion of the NORs in the booduga-terricolor lineage probably by transposition, and relocalization of the NORs in the terricolor complex by centric reorganization during the process of replacement of the Mus musculus-related AT-rich heterochromatin with the terricolor-specific heterochromatin.     

A rapid technique for producing silver-stained nucleolus organizer regions and trypsin-Giemsa bands on human chromosomes

Summary A simple and rapid technique is described whereby the nucleolus organizer regions (NORs) of human chromosomes can be differentially stained with silver. This staining is followed by trypsin-Giemsa banding on the same metaphase chromosomes. The metaphases simultaneously exhibit silverstained NORs and G bands, allowing for the unequivocal identification of all chromosomes and greatly facilitating studies involving the NOR-bearing acrocentrics.     

Age-related morphometric changes in the pineal gland. A comparative study between C57BL/6J and CBA mice

Relatively little is known about the effects of melatonin on the aging of the pineal, the organ which is the main place for synthesis of this hormone. Using simple morphometric methods, some parameters of the pineal gland, such as total volume, number of pinealocytes and pinealocyte volume were estimated in two mice strains: normal CBA and melatonin-deficient C57BL/6J. Two age groups, 6 weeks and 10 months, were studied in order to evaluate possible differential age-related changes between both strains. Pineals of both strains have similar morphometric and morphological features at 6 weeks of age. This suggests that pineal development, which has already concluded at 6 weeks of age, is not affected by the absence of melatonin synthesis in the pinealocytes. Later on, CBA pineal showed an increase in size caused by cellular hypertrophy. In contrast, the C57BL/6J pineal volume decreased by loss of pinealocytes in the same period of time. Semithin sections analysed by light microscopy did not show that this cell death was evident in the C57BL/6J strain at any of the ages studied. Thus, a gradual loss of pinealocytes could be hypothesised in these pineals. These results suggest that pineal melatonin could have a role in the maintenance of pinealocyte viability and the increase of pineal size which takes place after development. The abnormal pattern observed in the C57BL/6J pineal should be taken into account in future studies on this gland.     

The development of diploid parthenogenetic mouse embryos of the inbred C57BL and CBA strains]

We studied preimplantation development in vitro and postimplantation development in vivo of diploid parthenogenetic mouse embryos of C57BL/6 and CBA strains, as well as of (CBA x C57BL/6)F1 hybrids. Development to blastocyst stage of diploid eggs obtained from C57BL/6, CBA, and hybrid mice was observed in 90, 15, and 73% cases, respectively. After implantation, C57BL/6 embryos did not develop to somite stages, while CBA and hybrid embryos reached various stages of somite formation in 45 and 30% cases, respectively. Cultivation of embryos beginning from one-cell stage in the medium containing 2% newborn calf serum increased the yield of blastocysts from 15 to 59% in CBA embryos and from 73 to 90% in hybrids; However, such effect was not observed with C57BL/6 embryos. The latest stages of development observed in CBA and hybrid diploid parthenogenetic embryos were 33-35 somites and 25-30 somites, respectively. Imprinting patterns in chromosomes of CBA and C57BL/6 gametes are discussed.     

Population heteromorphisms of Ag-stained nucleolus organizer regions (NORs) in the acrocentric chromosomes of East Indians

Summary The nucleolar organizer regions (NORs) of acrocentric chromosomes in 70 normal East Indians were examined by Ag-staining (NSG) and acridine orange reverse banding (RFA) techniques. The Ag-stainability of NORs was variable from one individual to another but characteristics were constant within each individual. The average modal number of Agpositive NORs per individual was eight. A racial difference in the expression of NORs is suggested. to study the heteromorphism of NORs, the NSG technique was found to be more useful than RFA. Furthermore, it is concluded that there is no direct relationship between a heteromorphism of NORs identified by NSG and that identified by the RFA technique. Quantitative data on these differences is provided. In addition NOR-regions are classified into five sizes namely; very large, large, medium, small, and very small using subjectively defined criteria.     

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.     

Localization of phosphoprotein C23 to nucleolar structures and to the nucleolus organizer regions

After extraction of Novikoff hepatoma nucleoli with 4 M urea/3 M LiCl, phosphoprotein C23 was isolated by DEAE-cellulose and Bio-Rad AG3-X4A column chromatography. Immunization of rabbits with the highly purified protein C23 resulted in the production of a specific antibody as determined by Ouchterlony diffusion analysis. When the immunoperoxidase method was used to localize protein C23 in cells, it was found in ‘fibrillar centers’ (nucleolonemas) in nucleoli. Protein C23 was also demonstrated to be present on the nucleolus organizer regions (NORs) of metaphase chromosomes.     

The ultrastructure and argentophilic properties of the nucleolus organizer and centromeric regions of the chromosomes in early mouse embryogenesis

The Ag-staining of metaphase chromosomes in one-cell mouse embryos shows that the nucleolus organizer regions (NORs) are Ag-negative, whereas centromeric regions (CRs) are Ag-positive. Starting from 8-16-cell embryos, NORs stained by AgNO3 constantly, CRs remaining argentophobic. On the ultrathin sections of multicell embryos, Ag(+)-NORs differ from the chromosomal arms: they consist of loosely filaments about 6-8 nm in diameter, characterized by a low electron density. On the contrary, at one-cell stage Ag(-)-NORs are not morphologically identified: chromosomal bodies consist of uniform DNP-fibrils about 20 nm in diameter. These data permit to suppose that extended rDNA may form supranucleosomal and nucleosomal DNP-fibrils in the absence of Ag-proteins. The Ag(+)- and Ag(-)-CRs contain 10-20 nm DNP-fibrils mainly, although their density at multicell stages is higher than in one-cell mouse embryos.     

Detection of nucleolus organizer regions in chromosomes of human,chimpanzee, gorilla,orangutan and gibbon

Nucleolus organizer regions were detected by the Ag-AS silver method in fixed metaphase chromosomes from human and primates. In the human, silver was deposited in the secondary constriction of a maximum of five pairs of acrocentric chromosomes: 13, 14, 15, 21 and 22. The chimpanzee also had five pairs of acrocentric chromosomes stained, corresponding to human numbers 13, 14, 18, 21 and 22. A gibbon had a single pair of chromosomes with a secondary constriction, which corresponded to the nucleolus organizer region. In each case the Ag-AS method detected the sites which have been shown by in situ hybridization to contain the ribosomal RNA genes. An orangutan had eight pairs of acrocentric chromosomes stained with Ag-AS, probably corresponding to human numbers 13, 14, 15, 18, 21 and 22, plus two others. Two gorillas had silver stain over two pairs of small acrocentric chromosomes and at the telomere of one chromosome 1. The larger gorilla acrocentric chromosomes had no silver stain although they all had secondary constrictions and entered into satellite associations.