alpha-Fetoprotein and albumin genes are in tandem in the mouse genome.

Abstract

The murine a-fetoprotein (AFP) and serum albumin genes most probably arose in evolution as the consequence ofa duplication ofa common ancestral gene. They have both been previously mapped to chromosome 5 in the mouse. We now have evidence that these genes are closely linked. By using a unique copy DNA probe derived from previously cloned AFP 5' flanking DNA, a recombinant DNA phage has been isolated, from a bacteriophage DNA library, that contains sequences flanking the 5' end of the AFP gene and the 3' end of the albumin gene. Restriction endonuclease mapping and DNA sequence determination of the recombinant phage and comparison to total genomic DNA confirmed that the genes are in tandem, 13.5 kilobase pairs apart, with the albumin gene to the 5' side of the AFP gene. Thus, they are transcribed from the same strand of DNA.a-Fetoprotein (AFP), which is synthesized by the embryonic liver and yolk sac, is the major serum protein of the developing mammalian fetus (1, 2). In rodents, its rate of synthesis by fetal liver begins to decline just prior to birth, at a time when the rate of synthesis of serum albumin, the major adult serum protein, is increasing (3,4). This reciprocal expression ofAFP and albumin, coupled to a number offunctional and structural properties which they share (5, 6), led to the proposal that they were the products of a pair of duplicated genes. Two strong lines of evidence support this hypothesis. First, the complete mouse AFP amino acid sequence, deduced from direct determination of the nucleotide sequences of AFP cDNA and AFP chimeric cDNA plasmids (7), shows an overall 32% conservation of primary sequence with several mammalian albumins. Similar results have been obtained from more limited sequence comparisons ofthe human (6) and rat (8,9) proteins. Second, structural analysis of the mouse AFP and albumin genes, by using cloned segments of genomic DNA, revealed that both genes were organized identically into 15 coding segments interrupted by 14 intervening sequences (10, 11). The corresponding coding segments in each gene were the same size, although no nucleotide cross-hybridization was detected between them.More recently we have found that the two genes are present on chromosome 5 in the mouse (12). By using a series of hamster-mouse somatic cell hybrids in which the mouse chromosomes had differentially segregated, the presence of murine albumin and AFP DNA sequences was detected by hybridization and correlated to the presence of mouse chromosome 5 in the cell lines. In the present report, the close linkage ofthe AFP and albumin genes is demonstrated by the isolation and characterization of a recombinant genomic DNA clone whose sequences span the distance between them. MATERIALS AND METHODSIdentification of Unique Copy DNA Flanking the AFP and Albumin Genes. DNA from AAFP14 (11) was cleaved with several restriction enzymes (New England BioLabs) in both single and double digestions. The fragments were electrophoresed through 1.5% agarose gels and transferred from the agarose gels...

Characterization of Distant Enhancers and Promoters in the Albumin-α-Fetoprotein Locus during Active and Silenced Expression

“…The two genes diverged from a single 15-exon gene 300 -500 million years ago, but unlike most genes with a similar degree of relationship, they have remained next to each other, on rat chromosome 14, mouse chromosome 5, and human chromosome 4 (3,4). Such conservation of locus structure is generally an indicator of common regulation.…”

“…Computer analysis also predicts that these factors bind the AFP gene Ϫ4.3-kb (E2) and Ϫ2.7-kb (E1) enhancers. 3 Thus C/EBP binds all of the enhancers and promoters. In contrast, Foxa predominantly binds the enhancers while HNF1 is confined to promoters.…”

“…Other articles described transient assays of promoter and enhancer constructs in these cells (11,22) and we also characterized the relevant transcription factors (below). 3 This resource of cell lines and characterizations is the basis of a model system of enhancer and promoter function. The new experiments demonstrated that the albumin promoter and enhancer were active in both cell lines, while the AFP promoter and proximal enhancer were active in 8994 but repressed in H4E cells.…”

Distant Enhancers Stimulate the Albumin Promoter through Complex Proximal Binding Sites

“…In all three species, the albumin gene is 5Ј to the AFP gene, and the promoters are separated by about 30 kbp (7)(8)(9). The unusual conservation of the albumin/AFP locus suggests an arrangement necessary for coordinated regulation.…”

Transcriptional control of the murine albumin/alpha-fetoprotein locus during development.

“…Since that time, the murine genes have remained closely linked in tandem on chromosome 5, with the 3' terminus of the albumin gene 13.5 kilobases (kb) ofDNA to the 5' side of the AFP gene (7,8). The selective advantage to the organism for maintaining these genes in close proximity over such a long time span may reside in the development of cis-acting regulatory mechanisms that govern the expression of both genes during development.…”