A FISH study of chromosome fusion in the ICF syndrome: involvement of paracentric heterochromatin but not of the centromeres themselves.

We have used double fluorescence in situ hybridisation to study the involvement of centromeres and paracentromeric heterochromatin in the chromosome abnormalities seen in the ICF syndrome. To detect centromeres, we used a probe which labelled alphoid satellite DNA, and for the paracentromeric heterochromatin a probe for classical satellite II. Our results show that it is always the paracentromeric heterochromatin of the relevant chromosomes that becomes decondensed in this syndrome and which fuses to produce multiradial configurations. However, the centromeric regions, identified by their content of alphoid satellite DNA, appear never to become decondensed and always remain outside the regions of chromosome fusion in the multiradials.

The structure of the centromeric region of CHO chromosomes.

CHO chromosomes, prepared for fluorescence microscopy, or for scanning electron microscopy, sometimes show a splitting of the centromere proper into two sister centromeres, with a space between them, while the sister chromatids are joined in the most proximal regions of the chromosome arms. It is suggested that this might represent the final stage of chromatid splitting before the anaphase separation of chromatids.

Induction of diplochromosomes in mammalian cells by inhibitors of topoisomerase II.

Diplochromosomes, consisting of four chromatids lying side-by-side, instead of the normal two, are produced when cells go through two rounds of DNA replication without separation of chromatids. They are thus an indication of the failure of the normal chromosome separation mechanism. In the present experiments, induction of diplochromosomes by inhibitors of topoisomerase II (Topo II) was used to provide further evidence that Topo II is required for separation of daughter chromosomes. Actively growing cultures of CHO cells were treated with Colcemid, and separated into metaphase and interphase fractions, each of which was treated for 2 h with the Topo II inhibitor being tested. The cells were then cultivated in fresh medium without inhibitor for periods of between 18 and 44 h, and metaphase cells once again accumulated by treatment with Colcemid. Chromosome preparations were made in the standard way and stained with Giemsa. Up to 2,000 metaphases were counted from each culture, and the proportion with diplochromosomes calculated. At appropriate concentrations, the Topo II inhibitors etoposide and mitoxantrone induced substantial levels of metaphases with diplochromosomes in cultures that had been treated when the cells were in interphase (up to 30% and 11%, respectively). Amsacrine, however, only produced a smaller proportion (4.7%) of metaphases with diplochromosomes after a much longer culture period following treatment. All the inhibitors caused severe chromosome damage. When used to treat metaphase cells, mitoxantrone and amsacrine only induced diplochromosomes after prolonged culture, although a small number of diplochromosomes were seen after etoposide treatment and a shorter period of culture. Results with cells treated in metaphase might indicate that Topo II is, in fact, not required for anaphase chromosome separation, although it is clearly important for segregation of newly replicated DNA.

The cost of poor birth outcomes in employer-sponsored health plans.

OBJECTIVES: The authors examine the cost and incidence of poor birth outcomes in employer-sponsored health insurance plans. METHODS: An extensive study of national inpatient and outpatient claims data for prenatal, delivery, and postnatal care of nearly 59,000 mother-infant pairs was conducted. All maternal and infant costs incurred over a 2-year period were analyzed, and, furthermore, the longitudinal claims experience of a cohort of 20,000 mothers and infants was examined in detail. RESULTS: The study revealed that 25% of deliveries resulted in poor birth outcomes, which accounted for 40% of total costs over a 2-year period. Extrapolated nationwide, the net direct medical care cost of poor birth outcomes in employer plans has been estimated at approximately $5.6 billion for 1990, approximately 3% of aggregate after-tax corporate profits that year. CONCLUSIONS: Costs related to maternity and infant care are a major source of cost for employer-sponsored health insurance plans. Poor birth outcomes represent significantly higher cost for both the mother and infant at all stages of care-prenatal, at birth, and postnatal. To the extent that poor birth outcomes relate to maternal behavior and are preventable, their very high and protracted cost may justify substantial health promotion activity by employers and insurers.

Scanning electron microscopy of heterochromatin in chromosome spreads of male germ cells in Schistocerca gregaria (Acrididae, Orthoptera) after trypsinization.

Chromosome spreads, prepared from testes of the desert locust Schistocerca gregaria, were analyzed using scanning electron microscopy (SEM) after varying periods of preincubation in trypsin. The emphasis of the study was on the appearance of heterochromatin. A trypsin pretreatment of 5 sec resulted in a smooth surface on the chromatin throughout and the heterochromatin was highly electron-emissive. The facultatively heterochromatic X chromosome was clearly visible in interphase spermatogonia and in pachytene and late prophase I spermatocytes. Chromomeres of autosomal bivalents could be recognized in pachytene cells. Centromeric heterochromatin segments were very prominent in autosomes of late prophase I spermatocytes and some chromosomes showed interstitial and telomeric bands. Longer trypsin treatment (10 sec) resulted in a fine globular surface on the chromatin; however, the electron emission of heterochromatic chromosome segments was lower under these conditions. The result of trypsin pretreatment of euchromatin differed only slightly from that of the heterochromatin. Extensive trypsin treatment (20 sec) did not alter further the relative electron emission of heterochromatin and euchromatin, but the regular globular appearance was lost, apparently owing to damage on the chromatin surface. The loss of electron emission from the centromeric heterochromatin of the autosomes and the facultatively heterochromatic X chromosome after extended trypsin treatment suggests a central role of proteins in mediating the heterochromatic status in meiotic chromosomes of the locust. Information obtained using scanning electron microscopy of chromosome spreads is complementary to that obtained by C-banding in that facultative heterochromatin is visualized with particular clarity.

De novo chromosome formations by large-scale amplification of the centromeric region of mouse chromosomes.

Chromosomes formed de novo which originated from the centromeric region of mouse chromosome 7, have been analysed. These new chromosomes were formed by apparently similar large-scale amplification processes, and are organized into amplicons of approximately 30 Mb. Centromeric satellite DNA was found to be the constant component of all amplicons. Satellite DNA sequences either bordered the large euchromatic amplicons (E-type amplification), or made up the bulk of the constitutive heterochromatic amplicons (H-type amplification). Detailed analysis of a heterochromatic megachromosome formed de novo by an H-type amplification revealed that it is composed of a tandem array of 10-12 large (approximately 30 Mb) amplicons each marked with integrated "foreign' DNA sequences at both ends. Each amplicon is a giant palindrome, consisting of two inverted doublets of approximately 7.5-Mb blocks of satellite DNA. Our results indicate that the building units of the pericentric heterochromatin of mouse chromosomes are approximately 7.5-Mb blocks of satellite DNA flanked by non-satellite sequences. We suggest that the formation de novo of various chromosome segments and chromosomes seen in different cell lines may be the result of large-scale E- and H-type amplification initiated in the pericentric region of chromosomes.

The distribution of topoisomerase II on mammalian chromosomes.

The distribution of topoisomerase II (Topo II) has been studied using immunofluorescence on cytocentrifuged preparations of mammalian chromosomes. Immunolabelling of Topo II is affected by choice of fixative, by barriers to accessibility and by the lability of the enzyme. Chromosomes still embedded in cytoplasm remain unlabelled, while in contrast Topo II can easily be lost from some sites in chromosomes free of cytoplasm. The definitive distribution of Topo II consists of a line along the centre of each chromatid, corresponding to the chromosome core or scaffold, and quantities of Topo II elsewhere in the chromosomes which vary during the course of mitosis. A strong reaction for Topo II can be seen throughout prophase chromosomes, consistent with a role in condensation and/or segregation of the chromosome arms at this stage. At metaphase, Topo II is restricted to the centromeric regions, the only parts of the chromosomes that still have to be separated at this stage, while in anaphase, after segregation has occurred, this centromeric concentration of Topo II is lost. The distribution and quantity of Topo II in mammalian chromosomes is thus wholly consistent with the known functions of this enzyme in chromosome condensation and segregation.

Patterns of DNase I sensitivity in the chromosomes of the grasshopper Chorthippus parallelus (Orthoptera).

We have analysed the patterns of DNase I/nick translation in the chromosomes of the grasshopper Chorthippus parallelus erythropus. Sites of preferential DNase I-nicking were concentrated at the distal chromosome regions, thus showing the non-uniform DNase I sensitivity of different chromosome domains. Among centromeric C-bands, the heterochromatin of metacentric and acrocentric chromosomes differed with respect to their DNase I resistance.

Problems in preparation of chromosomes for scanning electron microscopy to reveal morphology and to permit immunocytochemistry of sensitive antigens.

Although much information about chromosome structure and behaviour has been obtained using light microscopy, greater resolution is needed for a thorough understanding of chromosome organisation. Scanning electron microscopy (SEM) can provide valuable data about these three-dimensional organelles. The introduction of methods using osmium impregnation of methanol-acetic acid-fixed chromosome spreads revolutionised matters, producing life-like images of chromosomes. Nevertheless, it became clear that osmium impregnation introduced various artefacts, although the resulting images were still useful. Methanol-acetic acid-fixed chromosomes are, in fact, flattened on the glass substratum, and the 3-dimensional appearance obtained after osmium impregnation is the result of swelling during this process. At the same time, the fibrous substructure of the chromosomes becomes much coarser. More recently a number of alternative methods have become available for studying chromosomes by SEM. Isolated chromosomes, that have not been allowed to dry during preparation, retain a 3-dimensional appearance without osmium impregnation, and the same is true of methanol-acetic acid-fixed chromosomes that have been treated with 45% acetic acid and processed without drying; however, these methods do not permit the routine production of intact metaphase spreads. Use of cytocentrifuge preparations obviates the use of acetic acid fixation and osmium impregnation, produces intact metaphase spreads, and permits the immunocytochemical detection of antigens that are easily destroyed by routine fixation procedures.

Comparison of methods for the detection of in situ restriction enzyme - nick translation using fluorochromes and confocal microscopy.

A series of experiments was carried out to determine the most efficient methods for detecting incorporated nucleotides in the "in situ" restriction enzyme - nick translation technique. Different methods were tested on fixed human metaphase chromosomes using confocal microscopy for the demonstration of the patterns produced. Of the various techniques tested, that using DIG-dUTP in conjunction with FITC-labelled anti-DIG appears to show the greatest sensitivity and specificity. The use of biotinylated nucleotides with FITC-avidin gives rather less sensitivity, while direct labelling with fluorescein-dUTP produces results more rapidly with better chromosome morphology but at the cost of reduced sensitivity. Resorufin-labelled dUTP was unusable, because of the low level of fluorescence and its very rapid fading. The successful fluorescence methods are more sensitive and faster than using horseradish peroxidase or alkaline phosphatase for detection.

ICF syndrome (immunodeficiency, centromeric instability and facial anomalies): investigation of heterochromatin abnormalities and review of clinical outcome.

A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described. This case is the second to be reported with consanguinity of the parents. This lends support to the theory of autosomal recessive inheritance. The features of the 15 published cases are reviewed. The clinical and cytogenetic characteristics of the syndrome are discussed, and new evidence provided as to the role of centromeres and centric heterochromatin in the production of chromosome aberrations. Correspondence with other authors has made possible a review of the clinical outcome in this condition.

Cytogenetic evaluation of the mechanism of cell death induced by the novel anthracenyl-amino acid topoisomerase II catalytic inhibitor NU/ICRF 500.

Anthracenyl-amino acid/dipeptides are novel topoisomerase (topo) inhibitors which can be actively cytotoxic in the low microM range. The present studies have been performed to determine whether cells treated with the topo II catalytic inhibitor NU/ICRF 500 (serine derivative) would manifest cytogenetic lesions consistent with its proposed mechanism of enzyme inhibition. Three other compounds were included for comparison: NU/ICRF 505 (tyrosine) which stabilises topo I cleavable complexes, NU/ICRF 602 (gly-gly) a non-cytotoxic catalytic inhibitor of topo I and II and NU/ICRF 502 (alanine) a non-cytotoxic non-topo inhibitor. Chromosomal damage was measured using the micronucleus test. NU/ICRF 500 (7.5-30 microM) induced an increase in CREST negative micronuclei (11-15 per 500 cells) in human lymphocytes (HL) and blocked the traverse of HL through the cell cycle, with cells accumulating in G2/M at 15 microM drug and G1/S at 30 microM drug. NU/ICRF 502 was without effect in the micronucleus test. NU/ICRF 500 and 602 (90-150 microM) caused no block in passage of synchronised metaphase Chinese hamster ovary cells through mitosis whereas NU/ICRF 505 produced a significant delay. DNA measurements of post-mitotic cells revealed that after NU/ICRF 500 treatment nuclei had a 4C DNA content, indicative of a lack of chromosomal segregation. Normal (2C) DNA content was observed with NU/ICRF 505 and 602. Overall, the data for NU/ICRF 500 are consistent with the cytogenetic modifications expected after catalytic inhibition of topo II and suggest that cell death may be mediated, at least in part, through this mechanism.

Inhibitors of topoisomerase II delay progress through mitosis and induce a doubling of the DNA content in CHO cells.

The effect of inhibition of topoisomerase II on chromosome segregation in CHO cells has been studied using cytogenetical techniques and measurements of nuclear DNA content. Cells were accumulated in metaphase, and their passages into the subsequent stages of mitosis, and into interphase, were examined. Of the compounds tested, five (Amsacrine, Etoposide, Hoechst 33342, Mitoxantrone, and nalidixic acid) greatly reduce the rate at which the chromosomes pass from metaphase through anaphase to the subsequent interphase and induce a high proportion of nuclei which contain a 4C amount of DNA. In several cases, the reformation of membranes around chromosomes can be seen although the chromosomes remain in a condition similar to metaphase, with the chromatids linked at the centromeres. Two other inhibitors of topoisomerase II, Hoechst 33258 and Merbarone, failed to delay cells in metaphase and did not induce tetraploidy. This failure may well be due to an inability of the compounds to penetrate the cells sufficiently quickly, or at a high enough concentration. Overall, the results are consistent with the hypothesis that topoisomerase II is essential for the segregation of chromosomes in mammals and other eukaryotes.

Patterns of DNase sensitivity in the chromosomes of Rana perezi (Amphibia: Anura).

We have analyzed the patterns of DNase I/nick translation in the chromosomes of Rana perezi. The results show a nonuniform DNase sensitivity in different chromosome domains; the hypersensitivity appears to be concentrated at both the NOR and the distal regions. The resemblance to the situation in mammals, where active genes are DNase I hypersensitive, is discussed.

The potential impact of diagnosis related group medical management on hospital utilization and profitability.

The potential impact of a proposed diagnosis related group (DRG) medical management model on hospital utilization and profitability was studied. The frequency and variable rates of hospitalization for patients with medical back problems, along with the myriad of diagnoses included in this DRG 243, made these patients an appropriate group to study and presented an excellent opportunity for assessing the potential impact of more effective and efficient DRG medical management.

Unusual chromosome structure of fission yeast DNA in mouse cells.

Chromosomes from the fission yeast Schizosaccharomyces pombe have been introduced into mouse cells by protoplast fusion. In most cell lines the yeast DNA integrates into a single site within a mouse chromosome and results in striking chromosome morphology at metaphase. Both light and electron microscopy show that the yeast chromosome region is narrower than the flanking mouse DNA. Regions of the yeast insert stain less intensely with propidium iodide than surrounding DNA and bear a morphological resemblance to fragile sites. We investigate the composition of the yeast transgenomes and the modification and chromatin structure of this yeast DNA in mouse cells. We suggest that the underlying basis for the structure we see lies above the level of DNA modification and nucleosome assembly, and may reflect the attachment of the yeast DNA to the rodent cell nucleoskeleton. The yeast integrant replicates late in S phase at a time when G bands of the mouse chromosomes are being replicated, and participates in sister chromatid exchanges at a high frequency. We discuss the implications of these studies to the understanding of how chromatin folding relates to metaphase chromosome morphology and how large stretches of foreign DNA behave when introduced into mammalian cells.

Functional aspects of the longitudinal differentiation of chromosomes.

The discovery of chromosome banding techniques over 20 years ago has revealed extensive longitudinal differentiation of chromosomes. This longitudinal differentiation can be classified into four types: heterochromatin, euchromatic bands, nucleolar organisers (NORs) and kinetochores. The telomeres, at the ends of chromosomes, cannot be detected by banding methods, but are clearly shown by in situ hybridisation. The functions of nucleolar organisers, kinetochores, and telomeres are reasonably well known, but the reasons for the differentiation of the greater part of the chromatin into heterochromatin and euchromatic segments remains uncertain. The function of heterochromatin may be sought in its centrometric location, where part of it is associated with the kinetochores, and another part appears to hold the sister chromatids together until anaphase. It appears that highly conserved nucleotide sequences are not required for these functions, but highly repeated sequences may be necessary. Nevertheless, these functions cannot explain the whole of heterochromatin. G-banding and other methods for euchromatic banding have shown that the euchromatic parts of chromosomes are divided into two major compartments, one gene-rich and the other gene-poor, which also differ in many other properties. The reason for this, which seems to be a fundamental property of chromosome organisation in eukaryotes, is totally obscure. Nevertheless, the observations that the greatest concentrations of genes tend to be found near the ends of chromosomes, and that the telomeres are often located at the nuclear envelope, suggest that a mechanism may have evolved to ensure that active genes are close to the cytoplasm.(ABSTRACT TRUNCATED AT 250 WORDS)