Search PubMed⌕ Search

Biomedical subjects

H G Coon

Publications and source records attributed to H G Coon.

At least 37 records · Page 2Linked to original sources
PubMed1976

Variation in aryl hydrocarbon (benzo(a)pyrene) hydroxylase activity in heteroploid and predominantly diploid rat liver cells in culture.

Aryl hydrocarbon (benzo(a)pyrene) hydroxylase is present and inducible in Buffalo rat liver cells in culture. There is substantial variation in both basal and inducible hydroxylase activities among heteroploid subclones isolated from a heteroploid parent population, and among diploid subclones isolated from a diploid parent population. This variation is not related to differences in the growth characteristics of the subclones, or to differences in their chromosome number. The results indicate that substantial heterogeneity in both basal and induced hydroxylase activity develops during the growth of both heteroploid and diploid cell strains in culture. These findings indicate that diploid cell populations are not necessarily homogeneous with respect to aryl hydrocarbon hydroxylas activity. This observation may complicate the interpretation of experiments involving somatic cell hybridization or polycyclic hydrocarbon-induced transformation and/or cytotoxicity. This heterogeneity in hydroxylase activity develops rather rapidly (2-3 mo of culture), in the absence of any apparent mutational stress.

Benz(a)Anthracenes↗
PubMed1975

Genetic heterogeneity in xeroderma pigmentosum: complementation groups and their relationship to DNA repair rates.

Fibroblast strains from 12 patients with xeroderma pigmentosum had lower than normal rates of DNA repair, as determined by autoradiographic studies of ultraviolet-induced unscheduled nuclear DNA synthesis. The nuclei in binuclear cells, obtained by fusing fibroblasts from certain pairs of these strains, had a greater rate of DNA repair than the nuclei of either strain's unfused mononuclear cells. These results indicate that complementary corrections of the strains' repair defects had occurred in the fused cells. Four complementation groups were found, indicating that at least four mutations caused decreased DNA repair among these 12 strains. The unfused mononuclear cells of each group had a characteristic rate of repair that differed from the rates of the other groups.

Autoradiography↗
PubMed1975

Neuronal properties of hybrid neuroblastoma X sympathetic ganglion cells.

Clonal mouse neuroblastoma cells without tyrosine 3-monooxygenase [EC 1.14.16.2; tyrosine hydroxylase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating)] activity were fused with normal cells from embryonic mouse sympathetic ganglia. One of the 37 hybrid cell lines obtained possesses high tyrosine 3-monooxygenase activity and synthesizes dopamine. These cells also have excitable membranes and generate action potentials in response to electrical stimuli. Thus hybrid cells, generated by fusion of neuroblastoma cells with normal cells from the nervous system, can acquire neural properties not found with the parental neuroblastoma cells.

Action Potentials↗
PubMed1975

Isolation from the asian mouse Mus caroli of an endogenous type C virus related to infectious primate type C viruses.

Treatment of a cell line derived from the Asian feral mouse Mus caroli with 5-bromodeoxyuridine induces an infectious, xentropic type C virus. This virus shares strongly cross-reactive reverse transcriptase (RNA-dependent DNA polymerase) and p30 antigens and crossinterferes with type C viruses isolated from a woolly monkey (SSAV) and gibbon apes (GALV). By similar criteria, the caroli virus is much less related to previously described type C viruses of the laboratory mouse, Mus musculus. Induction of virus from 10 of 13 single cell clones indicates that the virus is endogenous in Mus caroli cells. Thre results suggest that infectious primate type C viruses arose by trans-species infection(s) of certain primates with endogenous type C viruses from MUs caroli or a closely related Mus species.

Animals↗
PubMed1975

Expression of phenotypes in hybrid somatic cells derived from the nervous system.

The techniques of somatic cell hybridization allow a genetic analysis of differentiated functions of mammalian cells in vitro. Clonal lines of mouse neuroblastoma cells expressing a variety of differentiated neuroectodermal functions have been fused to L cells not expressing these functions. The resulting NL hybirds, on a clonal basis, express a variety of parental and non-parental phenotypes. Some hybrid clones inherit the ability to synthesize the neurotransmitter acetylcholine (Ach) (expression of high levels of choline acetyltransferase, CAT) while others do not. The ability to synthesize Ach and the ability to degrade this neurotransmitter (high levels of acetylcholinesterase activity, AChE) appear to segregate independently in NL hybrid progeny.--When a a variety of clonal cell lines replicating in culture are fused to cells freshly derived from the embryonic nervous system, interesting phenotypes result in the hybrid progeny. Neuroblastoma x rodent nervous tissue hybrids express AChE and in a few instances have developed the ability to synthesize CAT. Transformed human fibroblasts fused to normal rodent nervous tissue yield hybrid progeny that retain human and segregate mouse chromosomes and isozymes. No expression of differentiated functions has yet been found in these latter hybrids but they are useful for mapping mouse genes.

Acetylcholinesterase↗
PubMed1974

Interspecific recombination of mitochondrial DNA molecules in hybrid somatic cells.

The mitochondrial DNA (mtDNA) in rodent-human hybrid somatic cells was studied in strains that contain nucleotide sequences from both parental mtDNAs. A test for linkage of rodent to human mtDNA was devised on the basis of the density and sequence differences between these DNAs. When a mixture of rodent and human mtDNAs was banded in a CsCl gradient and each fraction hybridized with a mixture of complementary [(3)H]RNA transcribed from human mtDNA and complementary [(32)P]RNA transcribed from rodent mtDNA, each DNA was detected as a distinct and separate band at its expected density by specific hybridization with its complementary RNA. In some of the hybrid cell strains, the mtDNA sequences derived from the two species did not separate in the CsCl gradients. This result is interpreted as evidence for linkage between sequences from the two parental mtDNAs. While the exact nature of the linkage and the structure of the molecules containing both types of sequences are not known, the evidence supports the conclusion that the linkage is realized by a covalent bond. An event leading to the covalent bonding of these different sequences may be described as recombination. Among 18 hybrid cell strains examined, 13 contained large proportions of recombinant molecules. These molecules were found in both mouse-human and rat-human strains, and in strains containing more human or more rodent mtDNA sequences.

Animals↗
PubMed1974

The use of hybrid somatic cells as an approach to mitochondrial genetics in animals.

We have studied the fate of parental mitochondrial DNA (mtDNA) in hybrid somatic cells derived by Sendai virus-induced fusion of human cells and mouse or rat cells. Many hybrid cell strains were obtained which contained sequences from both human and rodent mtDNA after 40 to 60 population doublings. Some strains were subcloned and cultured further for up to 150 doublings; a large fraction of these strains contained both parental mtDNA sequences at that time. The relation between human and rodent mtDNA sequences was tested in some of the hybrid cell strains. In a high fraction of strains tested the human and rodent mtDNA sequences were linked to each other by what are most likely covalent bonds. This linkage may be described as "recombination" of mtDNA sequences from two different animals.

Animals↗
PubMed1972

Regulation of aryl hydrocarbon hydroxylase in intraspecific hybrids of human, mouse, and hamster cells.

Microsomal aryl hydrocarbon (benzo{a}-pyrene) hydroxylase is an enzyme complex highly inducible by various substrates. The activity of this enzyme complex was studied in hybrid cell strains obtained from parent cells that differ widely in basal as well as in induced enzyme activity. Hybrid cells were made from mouse fibroblasts, 3T3-4C2, with moderate basal and induced enzyme activity and the L-cell subline, A9, which has no detectable hydroxylase activity. Hybrid A9/3T3-4C2 cells exhibited enhanced basal and induced enzyme activities, which were 2- to 5-fold higher than those in 3T3-4C2 cells. In contrast, intraspecific hybrid cells of the human cell lines, JEC-3 and VA-2, and the hamster cell lines, OBP and BHK, exhibited a reduced basal and induced enzyme activity that was similar to or lower than that of the parent with low enzyme activity. In all hybrid cells examined, an association was observed between basal and induced enzyme activities, suggesting a closely coupled regulation of these activities.

Animals↗
PubMed1969

A quantitative comparison of formation of spontaneous and virus-produced viable hybrids.

Ultraviolet-inactivated Sendai virus used in conjunction with a selective system reproducibly gives high yields of viable hybrid cell lines. With two different crosses, the frequency of hybrid colonies obtained after virus treatment was found to be 100 times greater than the frequency of spontaneous hybrids, and this increase was found to show little variation between 33 and 1000 hemagglutinating units of virus. No differences have been found between the properties of hybrids obtained after Sendai treatment and those obtained from untreated mixed cultures of parental cells.

Animals↗
PubMed1966

Differentiation in vitro: effects of Sephadex fractions of chick embryo extract.

Chicken embryo extract has been fractionated into high-and low-molecular-weight components on Sephadex G-25. Media supplemented with the low-molecular-weight fraction (L) support full differentiation in clones of cartilage and of pigmented retina cells from chicken embryos. Growth rates of such cultures in L-supplemented media are greater than in media without embryo extract, and plating efficiencies are higher than in media with or without whole embryo extract. The high-molecular-weight fraction (H) in low concentrations also stimulates growth and plating efficiency, but inhibits the expression of differentiation.

Animals↗