G A Evans

α-Fetoprotein biosynthesis and hepatocellular differentiation

Biosynthesis of α-fetoprotein, a marker for differentiated fetal liver cells, was studied in RLA209-15 , rat fetal hepatocyte line that is temperature-dependent for differentiation. At 33°C, these cells showed characteristics of malignant transformation and synthesized only low levels of α-fetoprotein with an apparent molecular weight of 65,000. At 40°C, RLA209-15 cells regained the normal, differentiated phenotype and synthesized elevated levels of α-fetoprotein of two variants of 73,000 and 69,000 apparent molecular weight which co-migrated with the two fully processed forms of rat α-fetoprotein. The increase in α-fetoprotein synthesis at 40°C corresponded to an increase in mRNA for α-fetoprotein. The induction of α-fetoprotein indistinguishable from that produced by normal fetal hepatocytes demonstrates the reversion from the transformed to the differentiated state.

H-2 hemizygous mutants from a heterozygous cell line: role of mitotic recombination.

Variants that no longer express an entire H‐2 haplotype were readily isolated, by immunoselection with antisera directed against the haplotype, from an H‐2b/H‐2d heterozygous Friend leukemia cell line carrying a Robertsonian translocation of the chromosomes bearing the H‐2 genetic region. These variants can be denoted as being of the phenotype H‐2b‐ H‐2d+ or H‐2b+ H‐2d‐. Some of the H‐2b‐ H‐2d+ variants: (1) lack the restriction enzyme fragments characteristic of the missing H‐2b haplotype, as assessed by Southern blot analysis; (2) express more cell surface H‐2d antigens than wild‐type cells, as assessed by flow microfluorimetry; and (3) appear to have become homozygous for the more active H‐2d‐linked allele at the Glyoxalase I locus. These variants thus seem to have lost genetic material corresponding to the H‐2b haplotype and may have gained genetic material corresponding to the H‐2d haplotype. These results are consistent with the possibility that these variants were generated by mitotic recombination.