Hemoglobin synthesis in cell hybrids formed between teratocarcinoma and Friend erythroleukemia cells

Viable hybrid cells have been isolated following fusion of Friend erythroleukemia cells and undifferentiated teratocarcinoma cells. The hybrids formed between near-diploid parental cells resembled Friend cells in the ability to grow in suspension and to synthesize hemoglobin in the presence of the chemical inducers dimethyl sulfoxide (DMSO) and ouabain. Erythropoietin (EPO) was effective in inducing hemoglobin synthesis in some of the hybrid cell lines. The hemoglobins synthesized by the hybrids were of the adult forms, but were quantitatively different from those hemoglobins synthesized by the parental Friend cells, suggesting that the fusion event modulated the expression of the hemoglobin chain genes.

Heterogeneity of the ribosomal genes in mice and men

The structures of mouse and human ribosomal DNA were studied using the restriction enzymes Eco R1 and Hind III. Individual mice or humans showed a heterogeneous pattern of restriction fragments resulting from differences in the non-transcribed spacer DNA. Six individual mice from the inbred strain CBA/H-T6 had identical patterns. The same pattern was shown by another CBA strain and by C3H. These strains were originally derived from a BALB X DBA cross made in 1920. Different patterns were found for BALB/c, C57BL and Mus poschiavinus. Cultured cells derived from C3H mice (L cells) showed a pattern quantitatively different from that of the parent strain, but two myeloma cell lines derived from BALB/c showed the same pattern as BALB/c mice. Ribosomal DNA in man is also heterogeneous. Differences were observed between human DNAs in the amounts of the different spacer classes. Studies on mouse-human cell hybrids suggest that some spacer classes are present on more than one of the five human nucleolus organizers.

Delayed malignancy and altered growth properties of somatic cell hybrids between rat hepatoma and mouse L-cells

Somatic cell hybrids of mouse L-cells with rat HTC cells were studied for their growth properties in vitro and tumorigenicity in vivo. Three hybrid clones were selected for detailed study. All were delayed in tumor formation in nude mice compared with the parent lines despite their varied growth properties in vitro. One clone was sensitive to density dependent inhibition of growth (DDIG) and had a relatively low saturation density. A second clone was not sensitive to DDIG and had a higher saturation density. The third clone had atypical morphology, was insensitive to DDIG, and had a relatively high saturation density. All of the clones studied produced colonies suspended in agarose gel which were much smaller than those of the parents incubated for the same period of time. Only the pattern of growth in agarose gel corresponded to the delayed tumor formation in vivo of the hybrids. Sensitivity to DDIG and saturation density were not consistent with tumor growth. The hybrid clone that was sensitive to DDIG was the only one of the three that had a nearly complete set of chromosomes derived from each of the parents. The chromosome numbers of all three clones were unchanged after growth in agarose or as tumors in the nude mice.

Amounts of Epstein-Barr virus DNA in somatic cell hybrids between burkitt lymphoma-derived cell lines

The amounts of Epstein-Barr virus DNA in somatic cell hybrids between human lymphoid cell lines were found to be higher than in the parental cell lines, although the hybrids were not induced to spontaneous virus production.

In vivo hybridisation of cultured melanoma cells and isogenic normal mouse cells

Somatic cell hybrids were derived by fusing tumourigenic and melanogenic melanoma (PAZG) cells with normal diploid male mouse cells in vivo. Their chromosomal composition was equivalent to the sum of both parental genomes and included a Y chromosome lacking in the melanoma parent. Our study showed that in PAZG X C57BL hybrids (MP), tumourigenicity was suppressed but pigmentation was expressed.

Mouse-human heterokaryon analysis with a 33258 Hoechst-Giemsa technique

The bibenzimidazol derivative 33258 Hoechst can be used to distinguish microfluorometrically between mouse and human nuclei in heterokaryons. This affords a quick and accurate alternative to autoradiography in the analysis of such heterokaryons. The 33258 Hoechst fluorescence patterns can be converted after irradiation to a Giemsa rendition of the differential staining.

Ribosomal proteins of hamster, mouse and hybrid cells

We hhave been analyzing what could be considered to be structural ribosomal proteins, that is, those that remain with the ribosome when it has been subjected to centrifugation through 1.75 M sucrose, treatment with puromycin and KCl, and centrifugation through 0.5 M KCl and sucrose. By two-dimensional gel electrophoresis, a mouse-specific protein and a Syrian hamster-specific protein are detected, using liver or cultured cell lines. With liquid scintillation counting after two-dimensional gel electrophoresis it is possible to estimate the proportion of species-specific ribosomal protein in a mouse-hamster somatic cell hybrid.

Studies of the linkage relationship of beta-2-microglobulin in man-mouse somatic cell hybrids

Beta-2-microglobulin (beta2mu) production has been studied in 33 primary man-mouse hybrid clones and in 26 secondary man-mouse hybrid clones. These clones have also been examined for the presence of 15 human enzyme phenotypes. Karyotypic analyses have been carried out on clones. From these studies the following conclusions can be drawn: (1) Gene(s) determining human beta2mu production in humans are apparently syntenic with the MPI gene on chromosome 15. (2) Long-term fibroblast lines may be of limited use in mapping studies as chromosomal rearrangements frequently occur in these lines. (3) The gene(s) determining beta2mu production in humans segregate independently of chromosome 6. If the assignment of the genes determining HL-A alloantigens to chromosome 6 is correct, our results imply that beta2mu and HL-A alloantigens are determined by genes carried on different chromosomes, despite the fact that beta2mu forms an integral part of the HL-A molecule.

Human RNA transcripts in man-mouse somatic cell hybrids. II. Thermal denaturation studies and Cot analysis

The present report confirms an earlier finding that human RNA transcripts from a man-mouse somatic cell hybrid that has regularly retained only the human X chromosome can be identified by molecular hybridization on nitrocellulose filters. From thermal denaturation studies it is concluded that molecular hybrids between hybrid cell and human nucleic acids have higher Tm's, and thus greater specificity, than those between mouse and human nucleic acids. Additional data, utilizing the kinetics of molecular hybridization in solution (Cot analysis), demonstrate the presence of "few gene copy" DNA sequences in the above-mentioned hybrid cells that are complementary to human (HeLa) HnRNA. Also shown is a fraction of hybrid cell HnRNA that is complementary to "few gene copy" DNA sequences of human DNA. Thus, the experiments reported may represent a specific assay for identifying reiterated and "few gene copy" DNA sequences of the human X chromosome and their complementary RNA. Theoretically this experimental approach may be extended to any chromosome. Some of the short-term and long-term perspectives of these types of studies are discussed.

Somatic cell hybrids between mouse peritoneal macrophages and simian-virus-40-transformed human cells: II. Presence of human chromosome 7 carrying simin virus 40 genome in cells of tumors induced by hybrid cells

Cells derived from tumors induced in "nude" mice after injection of cells that were hybrids between mouse peritoneal macrophages and simian virus 40 (SV40)-transformed human cells were found to retain the human chromosome 7 carrying the SV40 genome, and indicate that the presence of human chromosome 7 carrying the SV40 genome is responsible for the expression of the tumorigenic phenotype in the hybrid cells.

Fate of mitochondrial DNA in human-mouse somatic cell hybrids (density gradient centrifugation-ethidium bromide-karyotype)

Several hybrid lines between human and mouse somatic cells, containing one or two complements of mouse chromosomes and a reduced complement of human chromosomes, have been examined for the presence of mouse and human mitochondrial DNAs. For this analysis, advantage was taken of the fact that these two types of mitochondrial DNA have a buoyant density difference in CsCl gradients of 0.008 g/cm(3). In all the hybrid clones analyzed, which retained an average number of human chromosomes estimated conservatively to vary from 5 to 23, only mitochondrial DNA of mouse character was detected. It seems likely that either repression of relevant human genes by the mouse genome or loss of human chromosomes is responsible for these results. If the latter explanation is true, since chromosome loss under the conditions used here was substantially a random process, one would have to assume that the activity of nuclear genes distributed in many chromosomes is required for the survival of mitochondrial DNA.