Somatic Interphase Cells Research Articles

Transcriptional Activity of Translocated NORs in Barley (Hordeum Vulgare L.)

ABSTRACTThe standard barley cultivar “Freya” and structural mutant forms ab, s, q, T21 and T627 were used to investigate the transcriptional activity of homologous rDNA loci (NORs) based on the positive reactions of NORs of metaphase chromosome with AgNO3 and the number and size of silver stained nucleoli in somatic interphase cells and meiocytes. Fluorescent in situ hybridization (FISH) was also used. The chromosomal rearrangement enables testing of intrachromosomal suppression of NORs and provides insight into the mechanisms of intraspecific nucleolar dominance.Considerable difference in gene expression (nucleolar dominance) after AgNO3 and FISH was established only in line ab, when both NORs (5H and 6H rDNA loci) are co-localized on the same or opposite arms of the chromosome. Translocation-induced intraspecific nucleolar dominance is probably the result of interaction of NOR6H and NOR5H or other genetic factors (like up-elements) located on the NOR-bearing chromosomes. The significance of such an unusual phenomenon is discussed.

Gene Expression of rDNA in Translocation Lines Of Barley (Hordeum Vulgare L.)

ABSTRACTTwo structural mutant forms of H. vulgare with reconstructed karyotypes—T505 and T506 have been studied with respect to the position and the activity of rDNA genes. On the basis of the AgNO3 staining and the number and size of silver stained nucleoli in somatic interphase cells and fluorescence in situ hybridization (FISH) we established a partial suppression of the expression of NOR7(5H) rDNA genes. When the NORs originally belonging to chromosomes 6(6H) and 7(5H) are combined in one chromosome, NOR6(6H) is dominant over NOR7(5H). Furthermore the dominance of the NOR6(6H) over NOR7(5H) is stronger when it is transposed. As shown by in situ hybridization the reason for the reduced nucleolus forming activity of NOR7(5H) is not due to eventual loss or deletion of rDNA.

Transcriptional activity of an inversion split NOR in barley (Hordeum vulgare L.).

The transcriptional activity of NORs in a new structural mutant of barley (PK-88-4) was studied based on the positive reaction of NORs of metaphase chromosomes with AgNO3 and the number and size of silver-stained nucleoli in somatic interphase cells and meiocytes. PK-88-4 proved to contain a pericentric inversion that split NOR 7 into two unequal parts residing in the opposite arms of the reconstructed chromosome 7(5). This chromosomal rearrangement enables testing of intrachromosomal suppression of NORs and provides insight into the mechanisms of intraspecific nucleolar dominance. Both parts of the split NOR proved to be transcriptionally active, and are not subject to intrachromosomal nucleolar dominance. Thus, translocation-induced intraspecific nucleolar dominance is probably the result of interaction of NOR6 and NOR7 or other genetic factors located on the NOR-bearing chromosomes 6(6H) and 7(5H).

Non-isotopic detection of nucleolar transcription in pre-implantation mouse embryos.

Nucleolar transcription was analysed in permeabilized pre-implantation mouse embryos at the four-cell, eight-cell, morula and early blastocyst stages using confocal microscopy to detect incorporated 5-bromouridine. The results demonstrated that the patterns of nucleolar transcription sites were common for all embryonic stages studied. They consisted most frequently of tightly associated groups of transcription foci similar to those encountered in somatic interphase cells. In addition, the nucleologenesis accompanying each cell cycle apparently gave rise to a different fluorescent pattern, that is to spatially separated fluorescent foci in the cells just after the resumption of rRNA synthesis. An immunoelectron microscopic analysis of the nucleolar transcription was also performed in the eight-cell embryos. A signal, usually consisting of clustered gold particles, was found specifically within nucleolar dense fibrillar components. This result was in agreement with established findings, which identify dense fibrillar component as the major site of nucleolar transcription in somatic cells.

Sex chromatin in lepidoptera.

Like mammals, Lepidoptera possess female-specific sex chromatin. In a compilation of new and published data, 81% of the 238 investigated Lepidoptera species display one or more heterochromatin bodies in female somatic interphase cells, but not in male cells. In contrast with the similar phenomenon in mammals, this sex-specific heterochromatin does not function as a dosage compensation mechanism. Most Lepidoptera have a WZ/ZZ sex chromosome mechanism, and the sex chromatin is derived from the univalent W sex chromosome. Sex chromatin is regarded as an indicator of an advanced stage of W chromosome evolution. In species with a Z/ZZ sex chromosome mechanism, loss of the W chromosome is accompanied by loss of the female-specific heterochromatin. Since sex chromatin can be discerned easily in interphase nuclei, and especially so in the highly polyploid somatic cells, it is a useful marker for diagnosing chromosomal sex of embryos and larvae, and of identifying sex chromosome aberrations in mutagenesis screens. All species with sex chromatin belong to the Ditrysia, the main clade of Lepidoptera that contains more than 98% of all extant species. Sex chromatin has not been reported for clades that branched off earlier. The nonditrysian clades share this character with Trichoptera, a sister group of the Lepidoptera. We propose that Lepidoptera originally had a Z/ZZ sex chromosome mechanism like Trichoptera; the WZ/ZZ sex chromosome mechanism evolved later in the ditrysian branch of Lepidoptera. Secondary losses of the W chromosome account for the sporadically occurring Z/ZZ sex chromosome systems in ditrysian families. The lepidopteran sex chromatin, therefore, appears to mirror the full evolutionary life cycle of a univalent sex chromosome from its birth through heterochromatinization to sporadic loss.

A new system for high-resolution DNA sequence mapping in interphase pronuclei

Cosmid clones containing human or hamster inserts have been hybridized in situ and localized with fluorescent reporter molecules in interphase nuclei (pronuclei) obtained after fusion of hamster eggs with either human or hamster sperm. Hamster egg cytoplasm processes the tightly packaged sperm DNA into large diffuse networks of chromatin fiber bundles, providing hybridization targets more extended than those available in somatic interphase cell nuclei. Pronuclear physical distances between hybridization signals were measured in micrometers and correlated to genomic distances determined by restriction fragment analyses, using cosmids from the Chinese hamster DHFR region and from the human Factor VIII/color vision pigment gene region (Xq28). The mean pronuclear distances between hybridization sites were about three times as large as those measured in somatic interphase cells for equivalent genomic distances. The relationship between physical and genomic distances was linear from less than 50 kb to at least 800 kb. The results show that physical distance in the sperm-egg system promises to extend the mapping range obtainable in somatic interphase nuclei below 50 kb and up to at least 800 kb.

Cell‐cycle aspects of growth and maturation of mammalian oocytes

In this review, recent data concerning growth and maturation of nonmammalian and mammalian female germ cells are compiled with regard to the increased understanding of somatic cells mitotic cycles, from yeast to human tissues. These data allow us to conclude that growing oocytes of nonvertebrates, lower vertebrates, and mammals resemble somatic cells in the G1 phase of the mitotic cycle in their metabolic and cell cycle behavior. Transcriptional and translational activity of growing oocytes and G1 somatic cells is not compatible with the activation of maturation promoting factor (MPF), with chromatin condensation or with nuclear membrane disintegration. Growing oocytes, even when they are in the dictyate stage of the first meiotic division, promptly inactivate MPF introduced into their cytoplasm by fusion or microinjection, just as do somatic interphase cells. In mammals, the LH surge induces "de novo" RNA and protein synthesis in granulosa cells. This metabolic change in granulosa cells abolishes their inhibitory activity, and meiosis in fully grown oocytes in preovulatory follicles is then resumed. Resumption of meiosis requires an activation of pre MPF molecules within oocytes. This can be achieved either without (mouse, rat, and rabbit) or with (pig, sheep, and cow) an active protein synthesis by the oocytes. The species specificity is probably dependent on the presence or absence of cyclin-like and/or mos-like molecules in fully grown oocytes. Both major events during GVBD, chromatin condensation, and nuclear envelope disintegration require protein phosphorylation. Experimentally, these two phosphorylation activities can be separated one from another. The active MPF molecules are amplified autocatalytically in amphibian and starfish oocytes. However, an increase of MPF activity in mouse and pig oocytes, similarly as in Rana pipiens and sturgeon oocytes, requires an active protein synthesis.

Injected mitotic extracts induce condensation of interphase chromatin

Although extracts from mitotic cells have been shown to induce chromosome condensation when injected into amphibian oocytes, they have not as yet been shown to induce this response in somatic interphase cells. In the experiments reported here, when mitotic extracts were injected into syncytial frog embryos, whose somatic nuclei were arrested in interphase, chromosome condensation was observed. The inability of interphase extracts, injected at similar concentrations, to induce this event demonstrates the cell cycle-specific accumulation of the factors responsible.

Specific staining of 9h in human somatic interphase cells by D 287/170.

Somatic interphase cells from males and females with normal karyotypes and with variants of the heterochromatic regions on chromosomes 9 and Y were stained with the fluorochrome D 287/170. The results showed that only 9h retained the ability to stain with D 287/170 in the interphase state, whereas 15ph and Yqh lost the specific staining pattern seen in metaphase. The number and size of the specific stained interphase bodies correlated with the ploidy of the cell population and the size of the 9h as seen in metaphase.

Interphase chromosome arrangement in Anopheles atroparvus.

The arrangement of chromosomes in interphase nuclei of Anopheles atroparvus has been inferred from an analysis of: 1. The early stages of mitosis as seen following Quinacrine staining, and 2. The reversible effects on the chromatin pattern obtained following the treatment of living cells with various NaCl solutions, and the following conclusions have been reached: (a) The chromatin is connected to the nuclear membrane, (b) Homologous chromosomes show close side-by-side somatic pairing, (c) The long arms of the sex chromosomes form a fluorescent peripheral body, (d) The autosomes are strongly reflexed at the centromeres, (e) The autosomal centromeric regions are polarized towards the peripheral body, (f) The telomeric regions of all the autosomes are closely apposed.--A ring-shaped pattern of interphase chromatin is constantly and reversibly induced by NaCl 0.15 to 0.18 M solutions.--These relationships indicate a peripheral arrangement of the interphase somatic complement.--The distribution of the chromosomes in polytene nuclei and at the beginning of meiosis resembles that suggested above for somatic interphase cells. This distribution may apply more widely in the Diptera.

END-TO-END, CHAIN-LIKE ASSOCIATIONS OF PAIRED PACHYTENE CHROMOSOMES OF CREPIS CAPILLARIS

Studies on the pachytene stage of meiosis of Crepis capillaris showed that the paired chromosomes are attached end-to-end forming chain-like configurations. The arrangements of the chromosomes in these tandem associations are according to the expectations based on the somatogram of this species. These observations make it very likely that the end-to-end chromosome associations present in all somatic interphase cells (Wagenaar, 1969) have their primary significance in the recognition and pairing of homologous chromosomes during early meiotic prophase.