Improved low cost ac-to-dc converter

Circuit converts an rms, ac voltage to a proportional dc voltage with good accuracy over a voltage range of approximately 6-1. It incorporates a pair of vacuum thermocouples in a dc feedback circuit

Rabl's model of the interphase chromosome arrangement tested in Chinise hamster cells by premature chromosome condensation and laser-UV-microbeam experiments

In 1885 Carl Rabl published his theory on the internal structure of the interphase nucleus. We have tested two predictions of this theory in fibroblasts grown in vitro from a female Chinese hamster, namely (1) the Rabl-orientation of interphase chromosomes and (2) the stability of the chromosome arrangement established in telophase throughout the subsequent interphase. Tests were carried out by premature chromosome condensation (PCC) and laser-UV-microirradiation of the interphase nucleus. Rabl-orientation of chromosomes was observed in G1 PCCs and G2 PCCs. The cell nucleus was microirradiated in G1 at one or two sites and pulse-labelled with 3H-thymidine for 2h. Cells were processed for autoradiography either immediately thereafter or after an additional growth period of 10 to 60h. Autoradiographs show unscheduled DNA synthesis (UDS) in the microirradiated nuclear part(s). The distribution of labelled chromatin was evaluated in autoradiographs from 1035 cells after microirradiation of a single nuclear site and from 253 cells after microirradiation of two sites. After 30 to 60h postincubation the labelled regions still appeared coherent although the average size of the labelled nuclear area fr increased from 14.2% (0h) to 26.5% (60h). The relative distance dr, i.e. the distance between two microirradiated sites divided by the diameter of the whole nucleus, showed a slight decrease with increasing incubation time. Nine metaphase figures were evaluated for UDS-label after microirradiation of the nuclear edge in G1. An average of 4.3 chromosomes per cell were labelled. Several chromosomes showed joint labelling of both distal chromosome arms including the telomeres, while the centromeric region was free from label. This label pattern is interpreted as the result of a V-shaped orientation of these particular chromosomes in the interphase nucleus with their telomeric regions close to each other at the nuclear edge. Our data support the tested predictions of the Rabl-model. Small time-dependent changes of the nuclear space occupied by single chromosomes and of their relative positions in the interphase nucleus seem possible, while the territorial organization of interphase chromosomes and their arrangement in general is maintained during interphase. The present limitations of the methods used for this study are discussed

Microdissection of human chromosomes by a laser microbeam

A laser microbeam apparatus, based on an excimer laser pumped dye laser is used to microdissect human chromosomes and to isolate a single chromosome slice

The architecture of chicken chromosome territories changes during differentiation

BACKGROUND: Between cell divisions the chromatin fiber of each chromosome is restricted to a subvolume of the interphase cell nucleus called chromosome territory. The internal organization of these chromosome territories is still largely unknown. RESULTS: We compared the large-scale chromatin structure of chromosome territories between several hematopoietic chicken cell types at various differentiation stages. Chromosome territories were labeled by fluorescence in situ hybridization in structurally preserved nuclei, recorded by confocal microscopy and evaluated visually and by quantitative image analysis. Chromosome territories in multipotent myeloid precursor cells appeared homogeneously stained and compact. The inactive lysozyme gene as well as the centromere of the lysozyme gene harboring chromosome located to the interior of the chromosome territory. In further differentiated cell types such as myeloblasts, macrophages and erythroblasts chromosome territories appeared increasingly diffuse, disaggregating to separable substructures. The lysozyme gene, which is gradually activated during the differentiation to activated macrophages, as well as the centromere were relocated increasingly to more external positions. CONCLUSIONS: Our results reveal a cell type specific constitution of chromosome territories. The data suggest that a repositioning of chromosomal loci during differentiation may be a consequence of general changes in chromosome territory morphology, not necessarily related to transcriptional changes

Analysis of chromosome positions in the interphase nucleus of Chinese hamster cells by laser-UV-microirradiation experiments

Unsynchronized cells of an essentially diploid strain of female Chinese hamster cells derived from lung tissue (CHL) were laser-UV-microirradiated (=257 nm) in the nucleus either at its central part or at its periphery. After 7–9 h postincubation with 0.5 mM caffeine, chromosome preparations were made in situ. Twenty-one and 29 metaphase spreads, respectively, with partial chromosome shattering (PCS) obtained after micro-irradiation at these two nuclear sites, were Q-banded and analyzed in detail. A positive correlation was observed between the frequency of damage of chromosomes and both their DNA content and length at metaphase. No significant difference was observed between the frequencies of damage obtained for individual chromosomes at either site of microirradiation. The frequency of joint damage of homologous chromosomes was low as compared to nonhomologous ones. Considerable variation was noted in different cells in the combinations of jointly shattered chromosomes. Evidence which justifies an interpretation of these data in terms of an interphase arrangement of chromosome territories is discussed. Our data strongly argue against somatic pairing as a regular event, and suggest a considerable variability of chromosome positions in different nuclei. However, present data do not exclude the possibility of certain non-random chromosomal arrangements in CHL-nuclei. The interphase chromosome distribution revealed by these experiments is compared with centromere-centromere, centromere-center and angle analyses of metaphase spreads and the relationship between interphase and metaphase arrangements of chromosomes is discussed

Formation of viable cell fragments by treatment with colchicine

Time-lapse cinematography of human fibroblasts revealed that mitotic cells separated into numerous cell fragments containing varying amounts of chromatin and cytoplasm when treated with colchicine. As cell fragments were very loosely attached to the surface of the culture vessel during their formation, they could be easily detached like mitotic cells by gently shaking the vessel and thus separated from normal interphase cells. Fragments obtained by this procedure were able to exclude trypan blue indicating, therefore, an intact cell membrane. When placed into Petri dishes many of them attached to and even spread out on the surface. Five hours later the majority of the attached fragments incorporated [3H]leucine. Time-lapse films showed that fragments were able to extend and retract pseudopodia at least for several hours after their formation. Although the fragments degenerated within a few days, in the present experiments the possibility was not excluded that fragments which had lost only a very small amount of chromatin and cytoplasm survived for longer periods of time. The observations clearly indicate viability of many newly formed fragments

Painting of human chromosomes with probes generated from hybrid cell lines by PCR with Alu and L1 primers

Specific amplification of human sequences of up to several kb length has recently been accomplished in man-hamster and man-mouse somatic hybrid cell DNA by IRS-PCR (interspersed repetitive sequence — polymerase chain reaction). This approach is based on oligonucleotide primers that anneal specifically to human Alu- or L1-sequences and allows the amplification of any human sequences located between adequately spaced, inverted Alu- or L1-blocks. Here, we demonstrate that probe pools generated from two somatic hybrid cell lines by Alu- and L1-PCR can be used for chromosome painting in normal human lymphocyte metaphase spreads by chromosomal in situ suppression (CISS-) hybridization. The painted chromosomes and chromosome subregions directly represent the content of normal and deleted human chromosomes in the two somatic hybrid cell lines. The combination of IRS-PCR and CISS-hybridization will facilitate and improve the cytogenetic analysis of somatic hybrid cell panels, in particular, in cases where structurally aberrant human chromosomes or human chromosome segments involved in interspecies translocations cannot be unequivocally identified by classical banding techniques. Moreover, this new approach will help to generate probe pools for the specific delineation of human chromosome subregions for use in cytogenetic diagnostics and research without the necessity of cloning