Clonal variants of mouse hepatoma cells that either fail to produce albumin (variant 19/2) or show significantly reduced levels (100-fold less) of albumin production (variant 1/c/1) were isolated from the parental line, Hepa la, after a single exposure to N-methyl-N′-nitrosoguanidine (MNNG). Intracellular levels of albumin in both variants were below detection by our assay. Analyses by cDNA-RNA reassociation kinetics indicate that there are approximately 3900 molecules of cytoplasmic albumin mRNA per cell in the parent and less than 10 molecules per cell in both variants. Southern blotting of the Eco RI restriction fragments of cellular DNA from the parent and variants did not indicate any major deletions in the albumin gene DNA sequences. We conclude that in the two variants studied, processes that regulate albumin production via alterations in the level of cytoplasmic albumin mRNA have been affected. Our analyses have also shown that alpha-fetoprotein (AFP) production is lacking in one variant (19/2) and is slightly reduced in the other (1/c/1). Transferrin secretion is lower than the parental line in both variants. Thus multiple nonlethal defects in hepatic gene expression can be obtained in Hepa la cells in culture that will be useful in determining the number and kinds of genes that control the expression of liver-specific loci.
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