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Expression of the mouse alpha-fetoprotein gene in embryonic, adult, and neoplastic tissues was assessed by RNA dot hybridization using 32P-labeled alpha-fetoprotein cDNA as probe, alpha-fetoprotein mRNA was present in high levels in total RNA from yolk sac endoderm, fetal liver, and an alpha-fetoprotein-producing hepatoma. In contrast, this mRNA was greatly depleted in total RNA from yolk sac mesoderm and essentially absent in brain, adult liver, and a non-alpha-fetoprotein-producing hepatoma. These results indicated that alpha-fetoprotein gene expression was controlled primarily at the transcriptional level. The presence of the modified base, 5-methylcytosine, in the alpha-fetoprotein gene was studied by comparing hybridization patterns obtained by Southern blot analysis of DNA cleaved with the restriction endonuclease isoschizomers Msp I and Hpa II. The gross sequence organization and reiteration frequency of the alpha-fetoprotein gene were invariant among the DNA samples, whereas, in each case, there was a positive correlation between hypomethylation of six CCGG (Hpa II) sites in the alpha-fetoprotein gene and expression of this gene. These Hpa II sites were distributed throughout a large portion of the alp]a-fetoprotein gene. Patterns of cytosine methylation in this gene were established before day 15 of gestation in yolk sac endoderm and mesoderm.
Andrews et al. (Sat,) studied this question.