Search PubMed⌕ Search

Biomedical subjects

J Zeuthen

Publications and source records attributed to J Zeuthen.

At least 145 records · Page 8Linked to original sources
PubMed1981

Chromosome banding and compaction.

We have described a characteristic substructure of mitotic chromosomes, the chromosomal unit fibre, with lengths about five times the length of the corresponding metaphase chromosomes and a uniform diameter of 0.4 micrometer. In order to study the relationship of chromosome banding to chromosome compaction, methods have been devised to obtain banding patterns on chromosomal unit fibres, similar to G-band patterns of intact mitotic chromosomes. The total number of bands plus interbands per haploid human karyotype is estimated at about 3000. The banding pattern of chromosomal unit fibres indicates a certain resemblance to the normal G-banding pattern of human chromosomes even if the details indicate a short-range random distribution.

Cells, Cultured↗
PubMed1981

Deficiency of malic enzyme: a possible marker for malignancy in lymphoid cells.

Soluble malic enzyme (MEs) has been examined in long-term human lymphoid cell lines cultured from 101 individuals. In 65 out of 66 lines derived from people without lymphoreticular malignancy the enzyme was very active. Lines established from 35 individuals with various forms of lymphoreticular malignancy were also examined, including in some cases more than 1 line derived from the same patient. In all cases where the cell line was thought to be derived from normal cells MEs was active, but in 27 out of 29 lines thought to be derived from malignant cells (from 25 patients) MEs was not detected. In the case of two patients with chronic lymphatic leukaemia 'normal' lines active for malic enzyme, and 'leukaemic' lines lacking malic enzyme, had been cultured from the same individual. Preliminary investigations of the lack of malic enzyme in somatic cell hybrids derived from lymphoma and leukaemia cell lines are compatible with an alteration at the level of the structural locus MEs on chromosome 6. However, the restoration of MEs activity in one line by fusion with mouse teratocarcinoma cells suggests that the alteration may be of a regulatory nature.

Animals↗
PubMed1980

Characterization of a human ovarian teratocarcinoma-derived cell line.

A cell line (PA I), derived from human ovarian teratocarcinoma cells, was obtained by culturing ascitic fluid cells from a patient with recurrence of malignant ovarian teratoma. During early passages the cultured cells showed a variable morphology, a long doubling time, and a low plating efficiency (2%). After about 50 passages in vitro, a cell population which was more homogeneous and resembled embryonal carcinoma cells were obtained. These cells had a shorter doubling time (26 h), and increased plating efficiency (77%). The early-passage cells were aneuploid (P 24) whereas the late-passage cells had a normal diploid karyotype with one balanced translocation between chromosomes No. 15 and No. 20 (P 224). Details of the karyotype suggest that the cells are heterozygous, i.e. derived from a stage before the first meiotic division. One of the two X chromosomes were inactive, and the cells expressed HLA antigens (A28 and B12), and beta 2-microglobulin. Expression of F9 antigen, characteristic of two-cell and later preimplantation embryos, was absent, while expression of PCC4 antigen, expressed also by blastocysts, was present. This finding suggests that the line might express some embryonic characteristics. The PA I cell line maintained in monolayer cultures showed several characteristics of malignant cells. The proportion of malignant cells increased with successive passages in vitro. The late-passage cells represented a fairly homogenous population of malignant cells similar to embryonal carcinoma cells. Late-passage PA I cells, when seeded under conditions that prevented attachment of cells to the substratum, formed embryoid bodies consisting of an inner core of cells similar to embryonal carcinoma cells, surrounded by a rind of endoderm-like cells. These two cell layers were separated by a basement membrane-like structure containing fibronectin. The core embryonal carcinoma cells expressed high alkaline phosphatase activity whereas the endoderm-like cells had low alkaline phosphatase activity. Embryoid bodies seeded on an adhesive substratum formed polycystic structures divided by layers of epithelial-like cells and containing extracellular fibrils similar to collagen type I or III. In these cultures, further limited differentiation into endoderm-like, epithelial-like cells and pigmented cells was observed. Morphological differenciation of undifferentiated PA I cells into endoderm-like cells in monolayer cultures could be obtained by treatment with BrdUrd or by plating in low serum concentration and at low density. Cells with characteristic fibrillar distribution of fibronectin and actin microfilament bundles were then observed, indicating formation of cells lacking properties of malignant cells. As indicated by these results, the PA I cell line, in spite of a limited capacity to differentiate in vitro, shares some of the properties of mouse teratocarcinoma cell lines and might therefore serve as a useful model for studies on some developmental mechanisms in human cells.

Antigens, Surface↗
PubMed1980

IgE production in vitro by two rat myeloma tumor lines (IR2 and IR162).

Two IgE-synthesizing rat myeloma tumor lines (IR2 and IR162) were maintained in growing cultures that were viable for prolonged periods of up to three months in the presence of primary fibroblasts. The production of IgE by explanted tumor cells was studied in short-term and long-term cultures. The IR 162 tumor line retained expression of both IgE heavy (H) and light (L) chain synthesis for up to three months under in vitro conditions, while the IR2 tumor line initially lost H chain expression after approximately one month in culture, followed by subsequent loss of L chain about one month later. Total polysomal RNA extracted from IR2 cells, before and after loss of IgE-expression, was separated by sucrose gradient centrifugation, and gradient fractions were analysed for poly(A)-containing mRNA by a [3H]poly(U)binding assay. The results for the long-term IR2 cultures showed a disappearance of mRNA sedimenting at 18-20 S and 15 S, found to represent H and L chain mRNAs, respectively. Furthermore, no IgE L chain mRNA sequences could be detected in long-term IR2 cultures when analysed by hybridization assays, using as a probe a 3H-labelled DNA complementary to IgE L chain mRNA, L chain mRNA sequences were also absent from the nuclear RNA in long-term IR2 cultures. The loss of IgE synthesis in long-term cultures of IR2 cells therefore appears to be correlated with a concomitant loss of IgE mRNA sequences indicating a dedifferentiation in vitro modulated at the transcriptional level.

Animals↗
PubMed1980

Hybridization of a myeloid leukemia-derived human cell line (K562) with a human Burkitt's lymphoma line (P3HR-1).

The myeloid leukemia-derived Epstein-Barr virus (EBV)-negative human lymphoid cell line K562 was successfully hybridized with the EBV-carrying Burkitt's lymphoma line P3HR-1. Authenticity of the hybrid PUTKO-1 was established by chromosome and isoenzyme studies. A virtually complete hybrid PUTKO-1 carried the EBV genome derived from the lymphoma parent. It averaged 26 EBV DNA copies per cell and was 100% positive for Epstein-Barr virus-associated nuclear antigen (EBNA). In most respects, the hybrid resembled the K562 parent: It had a high Fc receptor concentration, high sensitivity to natural killer cells, absence of EBV C3 receptors, and deficiency of membrane-associated beta 2-microglobulin (beta 2M) and HLA, in parallel with intracellular synthesis and secretion of beta 2M to the medium. Unlike the P3HR-1 parent, the hybrid was completely nonpermissive for antigens of the EBV cycle, early antigen, and viral capsid antigen. None of the 3 inducing agents, 5-lodo-2'-deoxyuridine, 12-O-tetradecanoyl-phorbol 13-acetate, or sodium butyrate, caused any viral antigen synthesis in PUTKO-1 in contrast to the good inducibility of the parental P3HR-1 subline. Thus the myeloid parent restricted expression of EBV antigens except EBNA. This exception further supports the concept that EBNA is an autonomous function of the viral genome, independent of host cell control that regulates expression of antigens related to the viral cycle. On the contrary, extinction of viral antigens in this hybrid between 2 cell lineages supports our previous concept that the ability to produce viral antigens is similar to a differentiated B-cell property.

Antigens, Surface↗
PubMed1979

Characterization of human chromosomal unit fibers.

A structural component of mitotic chromosomes that partially explains the compaction of DNA within mitotic chromosomes is suggested on the basis of the occurrence of long, regular cylindrical structures in preparations of isolated human chromosomes. These structures, "unit fibers", of a rather constant diameter of about 4,000 A have been postulated to be formed by coiling of the 250-300 A solenoid chromatin fiber that itself is formed by coiling of the 100 A string of nucleosome fiber. The human chromatid would thus be composed by a hierarchy of helices with contraction ratios for DNA at each level of coiling of 7 (string of nucleosomes), 5 (solenoid) and 40 (4,000 A "unit fiber" or "super-solenoid") which results in an overall contraction ratio for DNA in the "unit fiber" structures of about 1,400, which is approximately 5-fold less than the final contraction of DNA in intact chromatids of condensed metaphase chromosomes. The present report concerns more detailed studies with respect to the dimensions and cytochemical properties of the "unit fiber" structures observed in preparations of isolated human mitotic chromosomes that provide direct and indirect evidence in support of their "super-solenoid" structure and relate to known properties of human mitotic chromosomes.

Cells, Cultured↗
PubMed1979

Chromosomal unit fibers in Drosophila.

Chromosomal unit fibers consisting of long, regular fibers of about 0.40 micron diameter were obtained from disintegrated, isolated chromosomes of two Drosophila melanogaster cell lines. In one cell line with an essentially normal karyotype, three clearly defined size classes of 15,13, and 11 micron length were observed corresponding to the three larger chromosomes of Drosophila. In a cell line carrying an additional translocation between the two largest chromosomes a 19 micron fiber derived from the translocation chromosome was observed. Direct determinations of the DNA content per micron length of Drosophila unit fibers show that DNA is contracted by a factor of about 1400x in agreement with calculations based on the length of the unit fibers and the known DNA content of the individual Drosophila chromosomes. These findings support our previously proposed model for the unit fiber sub-structure of chromosomes as being derived by a hierarchy of coiling with the corresponding contraction ratios being 7 (100 A string of nucleosomes), 5 to 6 (250-300 A thick nucleohistone fiber), and about 40 (unit fiber), resulting in a total contraction of DNA in unit fibers in the order of 1400x.

Animals↗
PubMed1977

Somatic cell hybrids between human lymphoma lines. III. Surface markers.

Hybrids between two human lymphoma lines, Raji and Daudi (8A) and Raji BJAB (83) were examined for genetically determined and/or differentiation-related surface markers. HL-A B ce-l alloantigens, Fc and complement receptors, EBV receptors and beta2 microglobulin showed an autonomous ("co-dominant") expression in the hybrid. This is in contrast to most previous studies on other differentiation markers, involving as a rule crosses between cells of different lineages, where the differentiated pattern usually became "eclipsed" in the hybrid. Staining of activated complement and complement consumption tests showed intermediate or partially suppressed expression in the hybrids. This may be viewed in relation to the fact that these reactions do not merely depend on complement binding to the receptor, but also on subsequent activation and binding of the activated complement. A more complex interaction is also suggested for immunoglobulin production. Surface immunoglobulin showed a suppressive or intermediate pattern in both hybrids, whereas intracellular kappa chain production showed an amplification in the 83 hybrid. The beta2 microglobulin deficiency of the Daudi parent was corrected in the Raji/Daudi hybrid. Two new HL-A specificities,A10 and BW17, appeared on this hybrid which were not present on the parental lines. This suggests that the HL-A deficiency of the Daudi cell is due to its lack of beta2 microglobulin.

B-Lymphocytes↗
PubMed1977

Double immunoglobulin production in cloned somatic cell hybrids between two human lymphoid cell lines.

Several clones of independently established somatic cell hybrids between two human lymphoid cell lines, Raji and Namalwa, were examined for surface immunoglobulin expression. Double-antibody radioimmunoassays were established for kappa and lambda light chains. Immunoglobulins were detergent-extrated by Triton X-100 and quantified by radioimmunoassay. The Raji parent expressed small amounts of kappa chains on its surface, and the Namalwa parent a 10 fold greater amount of lambda chains. We show that the majority of the hybrid clones co-express both parental phenotypes.

Burkitt Lymphoma↗
PubMed1977

Spontaneous and induced patterns of the Epstein-Barr virus (EBV) cycle in a new set of somatic cell hybrids.

A somatic cell hybrid line and its subclones obtained by fusing two Burkitt lymphoma lines (Raji and Namalwa) were examined for the expression of EBV-specific antigens both spontaneously and after induction. The hybrids retained spontaneous early antigen (EA) production at the level characteristic of Raji. Similarly the more permissive Raji pattern dominated the induction of EA by IUDR treatment or P3HR-1 virus superinfection. These findings accord with our previous results on independently derived Raji/Namalwa hybrids. Virus capsid antigen was induced in the hybrids by P3HR-1 virus superinfection though at a lower level than in the Raji parental cell.

Antigens, Viral↗
PubMed1977

Higher-order structure of human mitotic chromosomes.

From observations on the partial disintegration of isolated human metaphase chromosomes we propose that human metaphase chromatids have a rather simple organization based on the folding and coiling of a long, regular, hollow cylindrical structure with a diameter of about 4000 A. This cylindrical structure, the unit fiber, is postulated to be a super-solenoid formed by the coiling of a 300 A solenoid, itself composed by coiling the basic string of nucleosomes. The structure of a human chromatid would thus be a hierarchy of helices, the contraction ratio of each coil, in ascending order of size, being approximately 7, 6, 40, and 5. This model appears to explain the estimated mass/unit length and accounts for many of the known features of human mitotic chromatids.

Chromosomes↗