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M C Weiss

Publications and source records attributed to M C Weiss.

106 records · Page 6Linked to original sources
PubMed1972

Expression of differentiated functions in hepatoma cell hybrids: induction of mouse albumin production in rat hepatoma-mouse fibroblast hybrids.

The synthesis of serum albumin has been studied in hybrids between well-differentiated rat hepatoma cells, which synthesize serum albumin, and mouse fibroblasts (3T3) that do not synthesize albumin. By immunodiffusion techniques with noncrossreacting antisera, the production of both rat and mouse albumin by the hybrids has been examined. Karyologically identified hybrids were produced between 3T3 cells and cells of a 1s hepatoma (Fu5) clone, and of a 2s hepatoma (2s Fu5-5cl.lE) clone. Each of the 3T3 x Fu5 hybrids produces only rat albumin. Among five 3T3 x 2s Fu5-5cl.lE hybrid clones isolated, one produces both rat and mouse albumin, two produce only mouse albumin, and two do not produce rat or mouse albumin.

Animals↗
PubMed1971

Expression of differentiated functions in hepatoma cell hybrids. I. Tyrosine aminotransferase in hepatoma-fibroblast hybrids.

The inducible enzyme tyrosine aminotransferase (TAT) has been investigated in hybrids between rat hepatoma cells and mouse fibroblasts. In the latter the TAT baseline activity is low, and in the presence of steroids does not change. By contrast, the hepatoma cells have high TAT activity, and this activity increases by a factor of 4-6 in the presence of steroids. The hybrid cells, like the fibroblasts, have low TAT activity and are not inducible. Heat inactivation curves demonstrate that the hybrid cells contain both parental forms of TAT, and therefore contain the parental genes specifying the enzyme. The presence in the hybrids of detectable rat TAT and the total absence of its inducibility suggest that a second gene is involved in the regulation of TAT inducibility, and that this gene is not expressed in the hybrids.

Animals↗
PubMed1971

Expression of differentiated functions in hepatoma cell hybrids: reappearance of tyrosine aminotransferase inducibility after the loss of chromosomes.

HYBRIDS FROM A CROSS OF RAT HEPATOMA CELLS WITH DIPLOID EPITHELIAL CELLS FROM RAT LIVER HAVE BEEN STUDIED WITH RESPECT TO KARYOTYPE AND EXPRESSION OF TWO FUNCTIONS LIMITED TO THE HEPATOMA PARENT: high level of the enzyme tyrosine aminotransferase (EC 2.6.1.5; L-tyrosine:2-oxoglutarate aminotransferase) and its inducibility with steroid hormones. The hybrids that contain the complete chromosomal complements from both parents show low enzyme activity and no inducibility. One hybrid clone, and all of its derivatives, which have lost 30-40% of the chromosomes initially present, show enzyme inducibility. Induction of tyrosine aminotransferase in the hepatoma and hybrid cells responds similarly to inhibition by cycloheximide and actinomycin D, and to steroid concentration. The enzymes from induced and noninduced hepatoma cells and from induced hybrid cells are similar in heat sensitivity and intracellular distribution; those from noninduced hybrid and diploid rat epithelial cells are different.

Animals↗
PubMed1970

Further studies on loss of T-antigen from somatic hybrids between mouse cells and SV40-transformed human cells.

The study of hybrids from three crosses between mouse cells and SV40-transformed human cells have established a positive correlation between the loss of human chromosomes and that of the SV40-induced T-antigen from the hybrid cells. These results, as well as those of other workers, provide strong support for the hypothesis of the integration of the SV40 genome in the chromosomes of transformed cells. Further, it has been shown that hybrid cells which have lost T-antigen are capable of synthesizing this antigen upon infection with SV40, thereby demonstrating that loss of the viral antigen from the hybrid cells is not due to loss of some cellular gene required for the expression of the viral genome. Results of karyological analyses of the hybrid cells argue against the existence of a single specific integration site for the SV40 genome in human cells.

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↗
PubMedDate not supplied

Albumin extinction followed by de novo methylation of its gene in somatic hybrids of a rat hepatoma.

We have previously identified an Msp I site at the 5' end of the rat albumin gene whose undermethylation is necessary but not sufficient for stable albumin expression in rat hepatoma cells. We have also shown that the extinction of albumin expression in somatic hybrids is not the result of methylation at this site, since for two different crosses, rapid extinction was found to occur in the absence of any de novo methylation of the previously active gene. In the present study, we examine albumin expression and albumin gene methylation for independent hybrid clones isolated from crosses between albumin expressing rat hepatoma cells and cells of two different non-expressing lines. The cells from hybrid clones of both crosses are characterized by stable extinction of albumin expression. Moreover, we find that de novo methylation of the "extinguished" albumin gene can occur in somatic hybrids, but only some weeks after the gene has ceased to be expressed.

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