Somatic Cell Genetics最新文献

Even though polyethylene glycol (PEG) has been shown to be a potent fusogen, it has not been widely exploited as an alternative to the Sendai virus for premature chromosome condensation (PCC) induction. A simple, rapid, and reproducible PEG protocol for primary cells in suspension is presented which allows satisfactory cell fusion and PCC indices, giving at the same time high cell viability and low giant, multinucleated cell formation. Technical details for PEG-mediated fusion and premature chromosome condensation induction in human and rat lymphocytes, rodent spleen cells, and spleen and whole body cells of newborn mice are provided. Further applications of the method are suggested.

We have mapped two new genes to chromosome 11 which control the cell-surface expression of two distinct antigens defined by monoclonal antibodies. One of the antigens has a general tissue distribution and is associated with a molecular complex of two polypeptides of 80,000 dalton and 40,000 dalton molecular weight. The second antigen has a restricted tissue distribution and is carried on a polypeptide of 100,000 daltons. We have used a combination of genetic and biochemical techniques to demonstrate that these new markers are distinct from the antigens defined by the monoclonal antibodies F10.44.2 and W6/34 which are also encoded by genes on chromosome 11. It is concluded that human chromosome 11 carries at least four distinct genes controlling cell-surface antigen expression.

The human gene for parathyroid hormone (PTH) was chromosomally mapped using human-rodent hybrids and Southern filter hybridization of cell hybrid DNA. A recombinant DNA probe containing human PTH cDNA insert (pPTHm122) hybridized to a 3.7-kb fragment in human DNA cleaved with the restriction enzyme EcoRI. By correlating the presence of this fragment in somatic cell hybrid DNA with the human chromosomal content of the hybrid cells, the PTH gene was mapped to the short arm of the chromosome 11.

In order to study the involvement of human chromosomes in the expression of liver-specific functions, we have produced somatic cell hybrids between a rat hepatoma (7777) cell line and human diploid skin fibroblasts (series XIX) or human fetal liver cells (series XXII). Production of human serum proteins was detected by immunoelectrophoretic analyses of concentrated serum-free hybrid culture supernatants. Human alpha 1-antitrypsin (AAT) was secreted by a subset of hybrids but not by the parental cells. The activated human AAT phenotype segregated concordantly with human chromosome 14 in 18 primarily HAT-selected and five azaguanine back-selected series XXII hybrids. All other chromosomes were excluded as playing a role in AAT expression. Therefore, the AAT gene (PI) is assigned to chromosome 14. This quasi-constitutive expression of a liver-specific function was not observed for the other serum proteins studied, nor was it seen in the skin fibroblast-derived hybrids (series XIX) although AAT was produced by some of them.

Inactivation of the X chromosome during mammalian spermatogenesis has been postulated to occur by the same mechanism that controls female somatic X chromosome inactivation. We have used DNA-mediated transformation of HPRT- cells to test this idea, because it has been shown previously that inactive X chromosome DNA from somatic cells will not transform HPRT- cells. Isolated DNA from the mature sperm of five mammals (human, mouse, horse, bull, rabbit) were all capable of HPRT transformation, and transformants were confirmed electrophoretically. Measures were taken to ensure that the transformation frequencies observed could not be due to somatic contamination. The positive HPRT transformation result indicates that mature sperm X chromosomal DNA is not modified in the same manner as that of female inactive X chromosomal DNA. Since there is evidence for methylation of the somatic inactive X chromosome, it is possible that methylation, at least for the genes studied, is not involved in sperm X chromosome inactivation.

Somatic cell hybrids obtained from the fusion of human B lymphocytes and an asparagine synthetase-deficient Chinese hamster ovary cell line were isolated after growth in asparagine-free medium. The human and hamster forms of asparagine synthetase differ significantly in their rate of inactivation at 47.5 degrees C. The asparagine synthetase activity expressed in the hybrids was inactivated at 47.5 degrees C at the same rate as the human form of the enzyme. Karyotypic analysis and analysis for chromosome-specific enzyme markers showed that the structural gene for asparagine synthetase is located on chromosome 7 in humans. The heat-inactivation profile for asparagine synthetase in extracts of hybrids formed between human peripheral leukocytes and a hamster cell line expressing asparagine synthetase activity was intermediate between the two parental types when human chromosome 7 was present, but was identical to the hamster parent when chromosome 7 was absent.

Cytotoxic plant lectins select for mutants which exhibit unique structural changes in surface carbohydrates reflecting specific defects in glycosylation reactions. However, lectins are not highly specific selective agents and, as a result, only the most frequently occurring mutants are obtained from single lectin selections. We have previously shown that the specificity of lectin selections may be improved by utilizing a combination of lectins added together or sequentially. This strategy has now been further exploited in the search for novel lectin-resistant mutants of Chinese hamster ovary cells. Five new LecR phenotypes have been uncovered. One belongs to a new, recessive complementation group, two behave dominantly in somatic cell hybrids, and the remaining two appear to represent new phenotypes which fall into previously described complementation groups.

Seven different Chinese hamster cell lines were found to vary greatly in their sensitivity to inhibitors of the mitochondrial ATPase. In plating-efficiency experiments, Chinese hamster lung V79 and bone marrow M3-1 cells were approximately 10,000-fold more resistant to oligomycin, 100-fold more resistant to efrapeptin, and 10-fold more resistant to ossamycin and leucinostatin than were ovary CHO or peritoneal B14 cells. In vitro experiments indicated that the increased resistance of V79 versus CHO cells to these inhibitors was due to an increased resistance of the mitochondrial ATPase. Heat-inactivation experiments indicated that there was a difference in the structure of the mitochondrial ATPase of V79 and CHO cells. Genetic experiments indicated that the difference in the sensitivity of V79 and CHO cells to inhibitors of the ATPase and the difference in the structure of the mitochondrial ATPase of V79 and CHO cells was due to a difference in both a nuclear and a cytoplasmic gene.

Human--hamster somatic cell hybrids have been obtained by fusion of a CHO line (NA31) doubly deficient in hypoxanthine guanine phosphoribosyltransferase and glucose 6-phosphate dehydrogenase (G6PD) with normal G6PD(+) human fibroblasts. Analysis of NA31 extracts has revealed that, although G6PD activity is nearly absent, significant activity can be detected with 2-deoxyglucose 6-phosphate as substrate, so that the mutant and normal forms of the enzyme can both be easily detected. The cell hybrids obtained express human G6PD. The human G6PD subunits are distributed in homodimeric molecules as well as in human--hamster heterodimeric molecules. However, whereas the amount of hamster G6PD subunits present in the hybrid is similar to that in the hamster parental cells, the amount of human G6PD subunits is decreased by 3- to 10-fold when compared to the human parental cell. These results indicate that either the expression of the G6PD gene or the stability of the gene product is altered in the hybrid. By mutagenesis and selection in diamide (a substance that oxidizes intracellular glutathione), we have isolated a clone with a 3- to 5-fold increase in human G6PD activity. This derivative may have an increased rate of expression of the human G6PD structural gene.

Fifty-four benzo[a]pyrene (BP)-resistant, aryl hydrocarbon hydroxylase (AHH)-deficient mutants were found to be recessive, while five were dominant. Hybrids between the former mutants and the wild-type were killed by BP, and possessed AHH activities of at least 0.5 (relative to the wild-type). Dominant-mutant--wild-type hybrids were resistant to BP and had activities of about 0.05. Additional experiments assigned the recessive mutants to three complementation groups, designated A through C. Group-B--group-C hybrids were exceptional in possessing a mean AHH activity (0.36), less than the value (0.5) expected from gene dosage. This deficiency was probably due, in part, to instability of AHH activity in these hybrids. However, all hybrids tested retained stable DNA complements, equal to the sum of those of their parents, for 140 days in culture. Previous studies have shown that group B and group C mutations both affect the functioning of a cytosolic receptor required for AHH induction (1).