Biomedical subjects

M O Ott

Publications and source records attributed to M O Ott.

23 records · Page 2Linked to original sources

PubMed1984

Tissue-specific expression is conferred by a sequence from the 5' end of the rat albumin gene.

We have constructed a transient expression vector containing 400 bp of rat albumin gene immediate 5'-flanking sequences inserted 5' to the bacterial enzyme chloramphenicol acetyl transferase (CAT). We have transfected various clones of rat hepatoma cells representing different states of expression of the liver phenotype with this vector (pALB-cat) and also with two control vectors containing viral promoters (pSVE-cat and pRSV-cat), and measured activity of the bacterial enzyme CAT in cellular extracts 48 h later. The albumin flanking sequences are able to direct highly efficient CAT expression, compared with the control vectors, only in cells which express their own albumin gene: the albumin-negative hepatoma cells are at least 100 times less efficient in expressing CAT after transfection with the pALB-cat plasmid than are the albumin-positive ones. An unexpected result of our study is the total inability of the rat albumin flanking sequences to direct expression in albumin-producing mouse hepatoma cells.

Acetyltransferases↗

PubMed1984

Albumin extinction without methylation of its gene.

In earlier work we identified at the 5' end of the rat albumin gene an Msp I site whose undermethylation appears to be necessary but not sufficient for stable expression of the gene in rat hepatoma cells. Here, we ask whether the block to expression of albumin production, which occurs when rat hepatoma cells are hybridized with cells that do not produce the protein, could be the result of de novo methylation of this site. In two types of somatic hybrids, rat hepatoma-mouse L cell fibroblasts, and rat hepatoma-dedifferentiated variant rat hepatoma cells, extinction occurs and is maintained during the first 5-15 generations after fusion. During this time the Msp I site of the now inactive rat albumin gene remained unmethylated.

Albumins↗

PubMed1982

Undermethylation at the 5' end of the albumin gene is necessary but not sufficient for albumin production by rat hepatoma cells in culture.

We have measured methylation of the albumin gene in clones of rat hepatoma cells that vary quantitatively in their rates of synthesis of albumin and in variant and hybrid cells that produce no albumin. Although the albumin gene is undermethylated for its entire length in rat liver, only the 5' end is ever undermethylated in hepatoma cells. Moreover, undermethylation of the 5' end of the gene appears to be necessary for stable expression of the albumin gene in hepatoma cells. Since undermethylation of this region is found in some variant cells that fail to produce albumin, it is not a sufficient condition for albumin gene expression. Despite the excellent correlation between undermethylation of the 5' end of the albumin gene and its stable expression, the results argue against the possibility that the methylated state of such genes during development determines whether they will or will not be expressed.

Albumins↗

PubMed1981

Expression of the albumin gene in rat hepatoma cells and their dedifferentiated variants.

Rat hepatoma clones whose cells do and do not produce albumin, as well as somatic hybrid between the two types of cells, have been examined for albumin mRNA. A direct proportionality between the rate of albumin production and the concentration of albumin mRNA sequences was found for all albumin-producing hepatoma and hybrid clones, indicating that rate of synthesis of the protein is determined by the concentration of its mRNA. Albumin-negative dedifferentiated variant and somatic hybrid cells contain fewer than one to five molecules of albumin mRNA per cell; the block in expression of the gene appears to be at the same (probably transcriptional) level in variants and their somatic hybrids.

Albumins↗

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.

Animals↗