Murine alpha-fetoprotein and albumin: two evolutionarily linked proteins encoded on the same mouse chromosome

Technology development at the interface of proteome research and genomics: mapping nonpolymorphic proteins on the physical map of mouse chromosomes

Data obtained from protein spots by peptide mass fingerprinting are used to identify the corresponding genes in sequence databases. The relevant cDNAs are obtained as clones from the Integrated Molecular Analysis of Genome Expression (I.M.A.G.E.) consortium. Mapping of I.M.A.G.E. clones is performed in two steps: first, cDNA clones are hybridized against a 10-hit genomic mouse bacterial artificial chromosome (BAC) library. Second, interspersed repetitive sequence polymerase chain reaction (IRS-PCR) using a single primer directed against the mouse B1 repeat element is performed on BACs. As each cDNA detects several BACs, and each individual BAC has a 50% chance to recover an IRS-PCR fragment, the majority of cDNAs produce at least a single IRS-PCR fragment. Individual IRS fragments are hybridized against high-density spotted filter grids containing the three-dimensional permutated pools of yeast artificial chromosome (YAC) library resources that are currently being used to construct a physical map of the mouse genome. IRS fragments that hybridize to YAC clones already placed into contigs immediately provide highly precise map positions. This technology therefore is able to draw links between proteins detected by 2-D gel electrophoresis and the corresponding gene loci in the mouse genome.

Linkage between vitamin D-binding protein and alpha-fetoprotein in the mouse

The albumin gene family consists of four evolutionarily related genes that code for serum transport proteins. In rodents, the genes for albumin, alpha-fetoprotein, and alpha ALB are physically linked within 100 kilobases of DNA. The fourth gene, Gc, encoding vitamin D-binding protein or group-specific component, maps to the same chromosome as the other family members, but linkage has not been established. This report describes the genetic and physical mapping of Gc in mouse and establishes that, although Gc is genetically linked to the other genes, its physical distance from them extends beyond the resolution range of yeast artificial chromosome cloning and pulsed-field gel electrophoresis.

Map of seven polymorphic markers on rat chromosome 14: linkage conservation with human chromosome 4

Seven polymorphic markers identified by polymerase chain reaction (PCR) amplification, including markers for six genes--DRD1L (dopamine receptor, D1-like-2), GLUKA (glucokinase), PF4 (platelet factor 4), ALB (albumin), AFP (alpha-fetoprotein), and BSP (bone sialoprotein)--and one anonymous locus (D14N52), were mapped to a single 67-cM linkage group with F2 intercross progeny of F344/N and LEW/N inbred rat strains. Two of these markers, ALB and AFP, have previously been assigned to rat Chromosome (Chr) 14, allowing assignment of this entire linkage group. Five of the markers--DRD1L, PF4, ALB, AFP, and BSP--have been physically mapped to a large region of human Chr 4 encompassing the p arm and the q arm to band q28. Homologs of two of the markers, ALB and AFP, have been mapped to Chr 5 in the mouse. Comparison of human Chr 4 with the homologous regions on Chr 14 of the rat and Chr 5 of the mouse indicated that linkage conservation with human Chr 4 extends over a greater region in the rat than in the mouse. The markers described here were found to be highly polymorphic in twelve inbred strains (F344/N, LEW/N, ACI/N, BUF/N, BN/SsN, LOU/MN, MNR/N, MR/N, SHR/N, WBB1/N, WBB2/N, and WKY/N). These polymorphic markers should be useful in genetic linkage studies of important phenotypes in rats.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: XXVII. Intermediate generalizations (Part B)

In this second section of generalizations, methylation, differentiation and carcinogenesis are reviewed. Special consideration is given to the alpha-fetoprotein gene which is used extensively as a model embryonic gene. Specific correlations are made between the glucocorticoid response element and the alpha-fetoprotein gene. A further correlation was made between retinoic acid and alpha-fetoprotein synthesis.

Cloning of human hepatic nuclear factor 1 (HNF1) and chromosomal localization of its gene in man and mouse

HNF1 is a transcription factor that is required for hepatocyte-specific expression of several genes, including albumin and fibrinogen. Rat HNF1-encoding cDNAs have recently been cloned, revealing that this factor is a distant member of the homeoprotein family. We have now isolated HNF1 clones from a human liver cDNA library by using a rat HNF1 cDNA-derived probe. The longest clone, HCL20, contains a sequence corresponding to the intact rat HNF1-coding region followed by a 3' nontranslated region and a poly(A) tail, hence representing an almost full-length HNF1 cDNA. Alignment of the human and rat sequences shows that HNF1 is highly conserved between the two species. The HNF1 gene was mapped by in situ hybridization and by RFLP analysis of interspecific mouse backcrosses to chromosomes 12q24.3 and 5F in human and mouse, respectively, establishing a new segmental homology between these two chromosomes.

The gene for the beta-subunit of retinal transducin (Gnb-1) maps to distal mouse chromosome 4, and related sequences map to mouse chromosomes 5 and 8

The heterotrimeric G protein transducin releases cGMP-phosphodiesterase from inhibition in retinal rod photoreceptor cells when stimulated by light-activated rhodopsin. As a result the level of cGMP goes down, the rod plasma membrane hyperpolarizes, and the release of neurotransmitter is modified. We have used a bovine cDNA for the beta-subunit of transducin (G beta 1) to map its gene Gnb-1 to distal mouse chromosome 4. This cDNA also identified two other homologous sequences in the mouse genome. One of the sequences was on chromosome 5 which we identified as the locus of Gnb-2, a second G protein beta-subunit gene. The other sequence was on chromosome 8 and is either a pseudogene or an as yet undiscovered third G beta-subunit gene, here termed Gnb-3.

Expression of the alpha-fetoprotein gene in adult rat liver

The adult rat liver contains three alpha-fetoprotein (AFP) mRNAs of 2.2 (minor), 1.7, and 1.5 kb. These transcripts share a common 3' sequence, but the 1.7- and 1.5-kb AFP mRNAs lack sequences present in the first seven 5' exons of the 2.2-kb AFP mRNA. S1 nuclease analysis maps the 1.7-kb mRNA at the 5' boundary of the eighth exon of the 2.2-kb AFP mRNA and the 1.5-kb mRNA in the middle of the eight exon. In a transformed fetal rat liver cell line, we have previously identified a 1.7-kb AFP mRNA which is encoded by an AFP cDNA (ARFP5) isolated from an adult rat liver cDNA library. The 90-bp 5' sequence of ARFP5, which is located in the seventh intron of the rat AFP gene, is not present in the 2.2-kb fetal AFP mRNA, although ARFP5 does contain nucleotide sequence present in the 2.2-kb AFP mRNA extending from the beginning of its eighth exon (nucleotide 873) to the 3' end. The 1.7-kb RNA in adult liver also hybridizes with the 90-bp 5' sequence of ARFP5, suggesting that the two 1.7-kb AFP mRNAs are similar. The developmental profile of these AFP transcripts shows that fetal rat liver contains mainly the 2.2-kb mRNA which decreases to a very low level around the fifth week after birth. The 1.7- and 1.5-kb AFP mRNAs can be visualized about the third and fourth weeks after birth, respectively, and are the major AFP mRNAs in the liver of rats that are older than 4 weeks. The levels of the AFP mRNAs in adult liver are approximately 0.4% of the AFP mRNA level in 18-day-old fetal liver. Both the 1.7- and 1.5-kb AFP mRNAs are actively translated; they direct the cell-free synthesis of two polypeptides of 50K and 44K. A 50K polypeptide is also the encoded product of the 1.7-kb mRNA in the transformed fetal rat liver cell line, suggesting that the 44K polypeptide may be encoded by the 1.5-kb AFP mRNA.

Conditions required for activation of the mouse albumin or alpha-fetoprotein gene in hybrids between mouse lymphoblastoma and rat hepatoma cells

Activation of two previously silent mouse hepatic genes has been investigated in hybrid cells between pseudodiploid mouse lymphoblastoma cells and hyperdiploid or hypertetraploid rat hepatoma cells. In this material, activation of the mouse albumin gene is a frequent event, whereas activation of mouse alpha-fetoprotein (AFP) occurs only in those cells that produce large amounts of albumin. Quantitative tests of hybrid populations for the activated proteins and their mRNAs revealed the expected sizes and structures: moreover, as in hepatoma cells, the amount of both rat and mouse albumin produced was directly proportional to the intracellular concentration of the corresponding mRNA. The cellular environment required for activation of the liver-specific genes was investigated by cell-by-cell analysis of each hybrid clone. Immunostaining for the presence of rat and mouse albumin and mouse AFP revealed unexpected heterogeneity in the phenotypes of the hybrid populations, which were found to contain cells that: (a) failed to express either of the proteins; (b) produced all three; (c) produced both rat and mouse albumin; or (d) produced rat albumin only. Karyotypic analysis indicated that the hybrid-cell phenotype depended on parental chromosome ratios rather than absolute numbers of chromosomes. It was found for albumin and mouse AFP that the fraction of immunostained cells was equal to the fraction of metaphases that contained a minimal rat-to-mouse chromosome ratio of 2.5 and 9, respectively. It is concluded that in those hybrids, expression of liver-specific genes is regulated by extinguishers, but in a dose-dependent fashion, suggesting the intervention of antagonistic activators from the rat hepatoma chromosomes.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

Three functional ribosomal protein genes are unlinked in mouse genome

The mouse chromosomes bearing three functional ribosomal protein (rp) genes were identified by Southern blot analysis of DNA from a panel of mouse-hamster hybrid cell lines. Unique sequence intron probes were used to distinguish the functional rp genes from their multiple processed pseudogene counterparts. The genes specifying ribosomal proteins S16, L30, and L32 were found to be on chromosomes 7, 15, and 6, respectively. Since these functional rp genes are widely dispersed in the mouse genome, coordinate regulation of their transcriptional activity cannot be accomplished by a structural alteration of a single chromosomal region. Rather, it would have to involve interactions with sequences or structural motifs that are common to all three genes.

Mapping of haploid expressed genes: genes for both mouse protamines are located on chromosome 16

Mouse spermatozoa contain two protamines with different amino acid sequences. By hybridizing Southern blots of a series of mouse-hamster somatic cell hybrids containing subsets of mouse chromosomes and a complete set of hamster chromosomes with 32P-labeled cDNAs for each mouse protamine, we assign the two mouse protamine genes to chromosome 16. This report presents the first evidence for chromosomal linkage of two sperm-specific, haploid regulated gene products.

Plasma-protein production by rat hepatoma cells in culture, their variants and revertants

A series of subclones of the H4II line of the Reuber H35 rat hepatoma produce substantial amounts of three plasma proteins, transferrin, alpha 1-antitrypsin and fibrinogen. Immunocytochemical staining demonstrated that each of these proteins is synthesized by essentially every cell of these cell populations. Cells of dedifferentiated variant clones either cease to produce the proteins, or exhibit a substantial reduction that is accompanied by variability in the synthetic activity of individual cells of the population. As previously observed with regard to angiotensinogen production, the variant clones clearly divide into two categories: those that show only a reduction in synthesis are able to give rise to revertants, whereas the negative clones fail to do so. Revertant cells exhibit a dramatic restoration of the synthesis of plasma proteins, which in some cases, exceeds by severalfold the rates seen in the differentiated clones of origin. In addition, the revertant cells synthesize alpha-fetoprotein, a function that is not expressed by H4II cells or its daughter subclones. Immunocytochemical staining revealed that, with regard to several plasma proteins including albumin, fibrinogen and alpha-fetoprotein, the cell populations of revertant clones are very heterogeneous, for only a fraction of the cells synthesizes each protein. Hybrid cells resulting from several types of crosses, exhibited extinction of the plasma proteins, the exception being transferrin, whose production was maintained, but at a reduced level and in only a fraction of the cells. Taken together, our results show that the expression of albumin and transferrin can be dissociated from one to another, and from that of fibrinogen, alpha 1-antitrypsin and angiotensinogen.

In vitro activation of bone marrow-derived T-and non-T-cell subsets by alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a major serum glycoprotein during embryonic and early postnatal life. A number of diverse biologic functions have been attributed to AFP, including osmotic and carrier function and immunosuppressive activity. In this study we demonstrate that AFP selectively stimulates in vitro proliferation of two distinct subsets of adult murine bone marrow cells. One population of AFP-reactive bone marrow cells expresses surface receptors for soybean agglutinin (SBA) lectin. SBA+ bone marrow cells are resistant to cytotoxic pretreatment with T-cell-specific antisera and are not retained on Ig-anti-Ig affinity columns. The absence of conventional T- and B-cell markers, coupled with the presence of SBA receptors, suggests that AFP-activated non-T bone marrow cells may belong to an immature set of B lymphocytes. A second population of AFP-responsive bone marrow cells expresses the Thy-1+ Lyt 1+2- phenotype characteristic of conventional mature adult T helper cells. The potential physiological relevance of the mitogenic effects of AFP on bone marrow cells with respect to immunoregulatory processes in the fetal/newborn environments is discussed.

A lethal deletion on mouse chromosome 7 affects regulation of liver-cell-specific functions: posttranscriptional control of serum protein and transcriptional control of aldolase B synthesis

Steady-state levels of mRNAs were determined for the serum proteins albumin, alpha-fetoprotein (AFP), and transferrin, as well as for aldolase B in livers of newborn mice homozygous for a radiation-induced lethal deletion (c14CoS) in chromosome 7. Deficiencies in synthesis and secretion of the serum proteins as well as in activities of certain liver-specific enzymes characterize these homozygotes. The results of RNA dot and gel-blot hybridizations with the respective cloned cDNA probes showed a decrease to one-fourth of aldolase B mRNA levels in homozygous mutant livers compared to normal littermates, in contrast to normal levels of mRNA sequences for the three serum proteins in the mutants. Furthermore, the mRNA sequences were shown to be present as mature mRNA molecules in both mutant and normal littermate livers. We suggest that the deficiencies of liver-specific serum proteins and those of the enzymes caused by the lethal deletions around the albino locus on chromosome 7 of the mouse are due to different causes. In the case of the liver-specific enzyme examined here--i.e., aldolase B--control at the level of transcription or of message stability is affected in the homozygous deletion mutants, whereas the deficiencies of serum proteins are not reflected on the mRNA level and owe their origin to an effect on a posttranscriptional or translational level. These results lend further support to the assumption that the deleted portion of the genome includes genes concerned with the control and regulation of liver cell differentiation.

Activation of a silent gene is accompanied by its demethylation

The phenomenon of gene activation by cell fusion makes it possible to study a gene when it passes from a silent to an active state. The relationship between methylation and activation of the mouse albumin gene has been investigated in two types of hybrid clones: mouse lymphoblastoma--rat hepatoma hybrids where activation is very frequent, and mouse L-cell--rat hepatoma hybrids where activation is a rare event. Analysis of the methylation pattern of seven MspI/HpaII sites that occur along the first 8000 bases of the mouse albumin gene has been performed. The entire 5' region is unmethylated only in albumin-producing cells (adult liver and hepatoma); in non-hepatic cells this region is heavily methylated. In hybrids between rat hepatoma cells and mouse cells of mesenchymal origin, the only regular change is the demethylation of the most 5' site (M1), which is systematically observed in clones where expression of the mouse albumin gene has been activated. Demethylation of this site, like activation of the mouse albumin gene, is gene dosage-dependent; it is systematic in the lymphoblastoma--hepatoma hybrids and rare in L-cell--hepatoma hybrids. We conclude that demethylation of this site is tightly coupled with activation of the gene and may well be a necessary prerequisite for activation.

Tandem arrangement of the albumin and alpha-fetoprotein genes in the human genome

A genomic clone containing human albumin mRNA sequences was isolated from a lambda phage gene library derived from a human hepatoma cell line that produces alpha-fetoprotein (AFP) and albumin. This clone was also found to hybridize with the 5'-flanking region of the human AFP gene. Restriction mapping and nucleotide sequencing revealed that the albumin and AFP genes are present in tandem, in the same transcriptional orientation, with the albumin gene 14.5 kb upstream of the AFP gene. We have also isolated a genomic clone carrying both the albumin and AFP gene sequences from human fibroblasts, which produce neither AFP nor albumin. This DNA showed a restriction map that was indistinguishable from that of the clone obtained from the hepatoma described above, demonstrating that no gross rearrangements of the intergenic DNA sequence are involved in control of expression of the AFP and albumin genes.

Locus unlinked to alpha-fetoprotein under the control of the murine raf and Rif genes

The levels of alpha-fetoprotein mRNA in mice are determined by at least two trans-acting, unlinked genes, raf and Rif. raf determines the basal levels of alpha-fetoprotein mRNA in adult mice, while Rif determines its degree of inducibility during liver regeneration. To determine whether these regulatory loci affect other structural genes, we screened a murine fetal liver cDNA library for clones containing mRNA sequences that decrease after birth. One such clone, termed pH19, was identified, and its mRNA was shown to be under the control of both raf and Rif. The single-copy gene for H19 mRNA was localized to chromosome 7, and genetic crosses established that it was unlinked to either raf or Rif. It encodes a 2.5-kilobase mRNA that was identified in those tissues that produce alpha-fetoprotein: visceral endoderm, liver, and fetal gut. The repression of H19 mRNA in neonatal liver occurs several days after the decrease in alpha-fetoprotein mRNA, whereas inductions of both mRNAs during the differentiation of F9 teratocarcinoma cells into visceral endoderm were identical. The tissue-specific expression of H19 mRNA is different from that of alpha-fetoprotein in that H19 mRNA was detected also in both cardiac and skeletal muscle where no alpha-fetoprotein mRNA is produced. Despite the fact that the levels of H19 mRNA decline to 1/10th to 1/20th in cardiac muscle after birth, the adult basal levels are not under the influence of raf. This observation argues that the raf gene is a tissue-specific regulator of mRNA levels.

Molecular mechanisms of extinction of liver-specific functions in mouse hepatoma rat fibroblast hybrids: extinction of alpha-fetoprotein gene

Somatic cell hybrids formed by the fusion of mouse hepatoma (BWTG3) and rat fibroblast (JF1) cells exhibit the extinction of mouse AFP gene expression. Analysis of HindIII digests clearly shows that both mouse and rat AFP genes are present in the hybrids. DNA-RNA hybridization data show that AFP mRNA is virtually absent in the somatic cell hybrids. Our studies indicate, therefore, that extinction of mouse AFP gene expression in somatic cell hybrids (BJ01, BJ50, and BJ140) occurs in the presence of the rat genes and that the mechanism of extinction involves processes that result in the loss of AFP mRNA. We propose that the mechanism may involve either the inhibition of transcription or an inhibition of the processing of the mRNA transcript.

Localization of the L1Md family of repeated sequences in the mouse albumin-alpha-fetoprotein gene complex

Studies on the beta-globin gene complex in the mouse have demonstrated the existence of repeated DNA sequences interspersed throughout the intergenic regions (1,2). These sequences are members of families of middle repetitive sequences and have been mapped to specific intergenic sites in the 60 kbp beta-globin complex. In this study we present evidence that members of this middle repetitive family of DNA sequences, the L1Md family, are interspersed throughout the mouse albumin and alpha-fetoprotein gene complex. Unlike those of the beta-globin complex, all of which are found in the intergenic regions, these sequences are localized within intron 12 of the albumin gene and intron 3 of the AFP gene as well as twice in the 13.5 kbp intergenic region that links the albumin gene to the AFP gene.

Induction of alpha-fetoprotein synthesis in differentiating F9 teratocarcinoma cells is accompanied by a genome-wide loss of DNA methylation

F9 teratocarcinoma cells can be grown as monolayers or aggregates, and upon treatment with retinoic acid they will differentiate into parietal or visceral endoderm, respectively. Visceral endoderm specifically synthesizes alpha-fetoprotein and albumin mRNAs, which are not found in parietal endoderm. In contrast, both endoderms produce enhanced levels of the major histocompatibility antigen (H2) mRNA compared with F9 cells. F9 cells contain highly methylated DNA as judged by restriction enzyme digestion. However, upon differentiation into visceral endoderm, there is a genome-wide loss of methylation in induced, silent, and constitutively expressed genes. Experiments in which methylation loss is induced via the methyltransferase inhibitor 5-azacytidine result in no induction of alpha-fetoprotein mRNA and no morphological differentiation, suggesting that methylation loss alone is not sufficient to induce the visceral endoderm phenotype. Likewise, 5-azacytidine treatment of differentiated cells does not result in enhanced expression of alpha-fetoprotein mRNA. However, the patterns of loss of DNA methylation at all sites examined after differentiation or 5-azacytidine treatment were remarkably similar, suggesting that the two occur by a similar mechanism, the inhibition of DNA methyltransferase activity. These results argue that the specificity for methylation loss at a given site is an inherent property of aggregated F9 cell chromatin. This system provides a model for studying a tissue-specific change in DNA methylation upon differentiation.

Chromosome maps of man and mouse II

Chromosome displays and listings are presented showing loci whose position is known in both man and mouse, in similar manner to our previous report (Dalton et al. 1981). There is now evidence for at least 27 conserved autosomal segments with two or more loci in the two species. The human and mouse chromosome maps show the location of homologous genes. The mouse map also shows the positions of translocations used in gene location and of some other genes used in linkage studies on them.

Re-expression of hepatic functions in mouse hepatoma X rat hepatoma hybrids

Neonatal hepatic functions are selectively extinguished in hybrids between mouse hepatoma cells, that express only fetal hepatic functions, and rat hepatoma cells expressing neonatal as well as fetal functions. A search for hybrid cells reexpressing these neonatal functions was undertaken to determine; (1) whether the selective extinction of neonatal functions is reversible and at what frequency, and (2) whether the re-expression of neonatal functions would be accompanied by modifications in the expression of fetal functions. The criterion used to obtain hybrids showing re-expression was glucose-free medium (G) where growth requires the presence of the extinguished gluconeogenic enzymes. Even though the parental cells are of the same histotype it proved difficult to obtain re-expression. Survivors in G- were obtained only from hybrids containing a greater than 1s complement of rat chromosomes; they reexpress not only gluconeogenic enzymes but also basal tyrosine aminotransferase activity, and the fetal hepatic function alpha-fetoprotein continues to be expressed in most of the clones. All survivors in G- display a significant loss of chromosomes and this loss concerns essentially mouse chromosomes.

Induction of alpha-fetoprotein synthesis in differentiating F9 teratocarcinoma cells is accompanied by a genome-wide loss of DNA methylation

F9 teratocarcinoma cells can be grown as monolayers or aggregates, and upon treatment with retinoic acid they will differentiate into parietal or visceral endoderm, respectively. Visceral endoderm specifically synthesizes alpha-fetoprotein and albumin mRNAs, which are not found in parietal endoderm. In contrast, both endoderms produce enhanced levels of the major histocompatibility antigen (H2) mRNA compared with F9 cells. F9 cells contain highly methylated DNA as judged by restriction enzyme digestion. However, upon differentiation into visceral endoderm, there is a genome-wide loss of methylation in induced, silent, and constitutively expressed genes. Experiments in which methylation loss is induced via the methyltransferase inhibitor 5-azacytidine result in no induction of alpha-fetoprotein mRNA and no morphological differentiation, suggesting that methylation loss alone is not sufficient to induce the visceral endoderm phenotype. Likewise, 5-azacytidine treatment of differentiated cells does not result in enhanced expression of alpha-fetoprotein mRNA. However, the patterns of loss of DNA methylation at all sites examined after differentiation or 5-azacytidine treatment were remarkably similar, suggesting that the two occur by a similar mechanism, the inhibition of DNA methyltransferase activity. These results argue that the specificity for methylation loss at a given site is an inherent property of aggregated F9 cell chromatin. This system provides a model for studying a tissue-specific change in DNA methylation upon differentiation.

Evolution of the albumin: alpha-fetoprotein ancestral gene from the amplification of a 27 nucleotide sequence

The genes for alpha-fetoprotein and albumin arose by duplication of an ancestral gene that contained three genetic domains. These domains were generated by the triplication of a primordial genetic domain composed of five exons or subdomains. That the primordial domain itself arose by amplification of a simpler sequence is suggested by nucleotide sequence homologies among the subdomains of the mouse alpha-fetoprotein gene. A detailed analysis of these homologies reveals that each of the five subdomain families contains remnants of a 27-base-long repeat from which the entire alpha-fetoprotein coding sequence has been assembled. A consensus sequence for the 27 nucleotide repeat is derived, and the positions of the repeats within each subdomain are described. A model is proposed for the evolution of the primordial domain by the amplification and divergence of the 27 base-pair sequence, along with the condensation of the repeats into subdomains separated by intervening sequences. It is postulated that the role of intervening sequences may be to limit sequence amplification in genes such as alpha-fetoprotein and albumin whose protein products cannot tolerate size variation.

Lengths of chromosomal segments conserved since divergence of man and mouse

Linkage relationships of homologous loci in man and mouse were used to estimate the mean length of autosomal segments conserved during evolution. Comparison of the locations of greater than 83 homologous loci revealed 13 conserved segments. Map distances between the outermost markers of these 13 segments are known for the mouse and range from 1 to 24 centimorgans. Methods were developed for using this sample of conserved segments to estimate the mean length of all conserved autosomal segments in the genome. This mean length was estimated to be 8.1 +/- 1.6 centimorgans. Evidence is presented suggesting that chromosomal rearrangements that determine the lengths of these segments are randomly distributed within the genome. The estimated mean length of conserved segments was used to predict the probability that certain loci, such as peptidase-3 and renin, are linked in man given that homologous loci are chi centimorgans apart in the mouse. The mean length of conserved segments was also used to estimate the number of chromosomal rearrangements that have disrupted linkage since divergence of man and mouse. This estimate was shown to be 178 +/- 39 rearrangements.

Assignment of the genes for the alpha and beta subunits of thyrotropin to different mouse chromosomes

A series of mouse-hamster somatic cell hybrids, containing reduced numbers of mouse chromosomes and a complete set of hamster chromosomes, was used to determine the chromosomal locations of the genes for the alpha and beta subunits of mouse thyrotropin. Cloned cDNA probes for each subunit, in conjunction with Southern blot analysis of DNA treated with the restriction enzyme BamHI, allowed for assignment of the alpha-subunit gene to mouse chromosome 4 and of the beta-subunit gene to chromosome 3. Mouse alpha-subunit gene sequences always segregated with chromosome 4 (concordant in 14 hybrids) and the enzyme markers phosphoglucomutase 2 and 6-phosphogluconate dehydrogenase. Mouse beta-subunit gene sequences always segregated with chromosome 3 (concordant in 15 hybrids). Thus, the genes for at least one of the glycoprotein hormones, thyrotropin, are on different chromosomes.

Structural integrity of the human albumin gene in congenital analbuminemia

The human serum albumin gene was analyzed by restriction endonuclease mapping of chromosomal DNA isolated from a patient with congenital analbuminemia. Following digestion with a variety of restriction endonucleases, the DNA from this individual produced the same fragments with homology to a serum albumin cDNA probe as did a control DNA specimen. Therefore, the genetic condition of congenital analbuminemia is not caused by any gross structural rearrangement or deletion of the gene itself, but may result from an abnormality in the gene's fine structure, perhaps affecting regulation or processing of the primary RNA transcript.

Transient expression of a mouse alpha-fetoprotein minigene: deletion analyses of promoter function

The constitutive transcription of a mouse alpha-fetoprotein (AFP) minigene was examined during the transient expression of AFP-simian virus 40-pBR322 recombinant DNAs introduced into HeLa cells by Ca3(PO4)2 precipitation. We tested three constructs, each of which contains the AFP minigene and pBR322 DNAs inserted in the late region of simian virus 40 and found that the relative efficiency of AFP gene expression was dependent on the arrangement of the three DNA elements in the vector. The transcripts begin at the authentic AFP cap site and are properly spliced and polyadenylated. To define a sequence domain in the 5' flanking region of the AFP gene required for constitutive expression, sequential 5' deletion mutants of the AFP minigene were constructed and introduced into HeLa cells. All AFP deletion mutants which retained at least the TATA motif located 30 base pairs upstream from the cap site were capable of directing accurate and efficient AFP transcription. However, when the TATA sequence was deleted, no accurately initiated AFP transcripts were detected. These results are identical to those obtained from in vitro transcription of truncated AFP 5' deletion mutant templates assayed in HeLa cell extracts. The rate of AFP transcription in vivo was unaffected by deletion of DNA upstream of the AFP TATA box but was greatly affected by the distance between the simian virus 40 control region and the 5' end of the gene. The absence of any promoter activity upstream of the TATA box in this assay system is in contrast to what has been reported for several other eucaryotic structural genes in a variety of in vivo systems. A sequence comparison between the 5' flanking region of the AFP gene and these genes suggested that the AFP gene lacks those structural elements found to be important for constitutive transcription in vivo. Either the AFP gene lacks upstream promoter function in the 5' flanking DNA contained within the minigene, or the use of a viral vector in a heterologous system precludes its identification.

Angiotensinogen production by rat hepatoma cells in culture and analysis of its regulation by techniques of somatic cell genetics

Angiotensinogen was synthesized by cells derived from the Reuber H35 rat hepatoma. Independent clones produced similar amounts of angiotensinogen, which corresponded to about four times more than expected for normal hepatocytes. The protein was secreted rapidly but could be visualized within cells using immunofluorescence. For one clone, it is shown that maximal angiotensinogen synthesis occurred during mid-exponential growth. Somatic cell genetics techniques have been used to investigate the regulation of angiotensinogen expression. Eleven clones of dedifferentiated variant hepatoma cells that failed to produce most or all of the liver specific proteins analyzed including albumin fell into two groups: Seven clones produced only 1-3% as much angiotensinogen as the differentiated clones, and four showed a reduction to 10-30%. Clones of the latter class were the only ones among the eleven analyzed that retained the potential to give rise to revertants, showing restoration of the differentiated state. All revertants fully restored angiotensinogen production, but only some of them re-expressed albumin. Somatic hybrids between differentiated hepatoma cells and one of the variants showed a substantial reduction in angiotensinogen production, whereas for some clones, albumin synthesis was fully maintained. These results show that regulation of the expression of angiotensinogen and of a second serum protein, albumin, was independent and that angiotensinogen synthesis was a faithful indicator of the general differentiation profile of all classes of clones.

Transient expression of a mouse alpha-fetoprotein minigene: deletion analyses of promoter function

The constitutive transcription of a mouse alpha-fetoprotein (AFP) minigene was examined during the transient expression of AFP-simian virus 40-pBR322 recombinant DNAs introduced into HeLa cells by Ca3(PO4)2 precipitation. We tested three constructs, each of which contains the AFP minigene and pBR322 DNAs inserted in the late region of simian virus 40 and found that the relative efficiency of AFP gene expression was dependent on the arrangement of the three DNA elements in the vector. The transcripts begin at the authentic AFP cap site and are properly spliced and polyadenylated. To define a sequence domain in the 5' flanking region of the AFP gene required for constitutive expression, sequential 5' deletion mutants of the AFP minigene were constructed and introduced into HeLa cells. All AFP deletion mutants which retained at least the TATA motif located 30 base pairs upstream from the cap site were capable of directing accurate and efficient AFP transcription. However, when the TATA sequence was deleted, no accurately initiated AFP transcripts were detected. These results are identical to those obtained from in vitro transcription of truncated AFP 5' deletion mutant templates assayed in HeLa cell extracts. The rate of AFP transcription in vivo was unaffected by deletion of DNA upstream of the AFP TATA box but was greatly affected by the distance between the simian virus 40 control region and the 5' end of the gene. The absence of any promoter activity upstream of the TATA box in this assay system is in contrast to what has been reported for several other eucaryotic structural genes in a variety of in vivo systems. A sequence comparison between the 5' flanking region of the AFP gene and these genes suggested that the AFP gene lacks those structural elements found to be important for constitutive transcription in vivo. Either the AFP gene lacks upstream promoter function in the 5' flanking DNA contained within the minigene, or the use of a viral vector in a heterologous system precludes its identification.

Somatic cell genetics and gene families

The utility of somatic cell genetic analysis for the chromosomal localization of genes in mammals is well established. With the development of recombinant DNA probes and efficient blotting techniques that allow visualization of single-copy cellular genes, somatic cell genetics has been extended from the level of phenotypes expressed by whole cells to the level of the cellular genome itself. This extension has proved invaluable for the analysis of genes not readily expressed in somatic cell hybrids and for the study of multigene families, especially pseudogenes dispersed in different chromosomes throughout the genome.

Genetic analysis of alpha-fetoprotein synthesis in mice

The differential induction of alpha-fetoprotein (AFP) mRNA during liver regeneration in three inbred strains of mice was examined to determine the genetic and molecular bases for the differences in protein production. BALB/cJ, C3H/He, and C57BL/6 mice, previously identified as high, intermediate, and low AFP producers, respectively, were used. Liver AFP mRNA concentrations during normal development and after carbon tetrachloride administration were measured and shown to correlate exactly with the serum protein concentrations. By performing a series of genetic crosses, we identified two unlinked genetic loci that acted independently to affect the inducibility of AFP mRNA. The raf gene, previously identified by Olsson et al. (J. Exp. Med. 145:819-827, 1977), determines the adult basal level of AFP mRNA, and the Rif gene affects its inducibility during regeneration. By using a polymorphic restriction endonuclease site within the albumin-AFP structural gene region, we show that neither regulatory gene is closely linked to the structural genes. In addition, neither gene affects the concentration of albumin mRNA during development or liver regeneration.

Genetic analysis of alpha-fetoprotein synthesis in mice

The differential induction of alpha-fetoprotein (AFP) mRNA during liver regeneration in three inbred strains of mice was examined to determine the genetic and molecular bases for the differences in protein production. BALB/cJ, C3H/He, and C57BL/6 mice, previously identified as high, intermediate, and low AFP producers, respectively, were used. Liver AFP mRNA concentrations during normal development and after carbon tetrachloride administration were measured and shown to correlate exactly with the serum protein concentrations. By performing a series of genetic crosses, we identified two unlinked genetic loci that acted independently to affect the inducibility of AFP mRNA. The raf gene, previously identified by Olsson et al. (J. Exp. Med. 145:819-827, 1977), determines the adult basal level of AFP mRNA, and the Rif gene affects its inducibility during regeneration. By using a polymorphic restriction endonuclease site within the albumin-AFP structural gene region, we show that neither regulatory gene is closely linked to the structural genes. In addition, neither gene affects the concentration of albumin mRNA during development or liver regeneration.

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

The ontogeny of expression of the alpha-fetoprotein (AFP) and albumin genes was examined in livers from late prenatal to 1-month-postpartum C3H/He mice. A parallel accumulation of both AFP and albumin mRNAs before birth, followed by a selective nonreciprocal decrease in AFP mRNA after birth, was observed. The decrease in AFP mRNA was the result of a decrease in transcription of the AFP gene, as measured by an in vitro nuclear transcription assay. We suggest a model for hepatic expression of the AFP and albumin gene cluster in which transcription of the two genes is activated simultaneously during differentiation and each gene is thereafter modulated independently in committed cells.

Generation and chracterization of variants of mouse hepatoma cells with defects in hepato-specific gene expression. I. Albumin synthesis variants

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.

Molecular mechanism of extinction of liver-specific functions in mouse hepatoma x rat fibroblast hybrids: extinction of the albumin gene

Hybrids formed by the fusion of mouse hepatoma (BWTG3) and rat fibroblast (JF1) cells exhibit the extinction of mouse albumin and alpha-fetoprotein synthesis. Karyotype analyses suggest that all parental chromosomes are present in the hybrids. The extinction, therefore, of mouse hepatocyte genes is attributed to the inhibitory action of the rat genome. In these studies, we show that these hybrids possess and express the mouse beta-glucuronidase gene (which is encoded on the same chromosome as the mouse albumin and alpha-fetoprotein gene), and we present data of Southern blot analysis which demonstrate that such hybrids have indeed retained both mouse and rat albumin DNA sequences. In addition, using mouse albumin cDNA, we have shown by cDNA-RNA reassociation kinetics that albumin mRNA is virtually absent in these hybrids. We conclude from these studies that the extinction of albumin synthesis involves a mechanism which results in the loss of cytoplasmic albumin mRNA.

Expression of human hepatic genes in somatic cell hybrids

Four diploid human cell types (lymphocytes, fibroblasts, amniotic fluid cells, and hepatocytes) were fused to mouse hepatoma cells, HH. HH synthesized and secreted several liver-specific gene products including albumin, transferrin, and alpha-fetoprotein. The resulting interspecific hybrids were compared to determine whether or not the pattern of human hepatic gene expression was similar when these various cells were fused with the mouse hepatoma line. The expression of six human hepatic genes was examined, including albumin, alpha-fetoprotein, ceruloplasmin, transferrin, alpha-1-antitrypsin, and haptoglobin. Albumin was most frequently expressed while alpha-fetoprotein was not detected in any of the hybrids studied. The patterns of expression of human serum proteins differed between the hybrid series. Hybrids derived from human fibroblasts produced primarily albumin, while those derived from lymphoblastoid cells and amniocytes had a higher frequency of clones secreting alpha-1-antitrypsin. The findings reported here suggest that the frequency of hybrid clones expressing human hepatic gene products and the array of proteins produced are influenced by the histogenetic state of the human parental cell type.

Localization of the casein gene family to a single mouse chromosome

A series of mouse-hamster somatic cell hybrids containing a variable number of mouse chromosomes and a constant set of hamster chromosomes have been used to determine the chromosomal location of a family of hormone-inducible genes, the murine caseins. Recombinant mouse cDNA clones encoding the alpha-, beta-, and gamma-caseins were constructed and used in DNA restriction mapping experiments. All three casein cDNAs hybridized to the same set of somatic cell hybrid DNAs isolated from cells containing mouse chromosome 5, while negative hybridization was observed to ten other hybrid DNAs isolated from cells lacking chromosome 5. A fourth cDNA clone, designated pCM delta 40, which hybridized to an abundant 790 nucleotide poly(A)RNA isolated from 6-d lactating mouse mammary tissue, was also mapped to chromosome 5. The chromosomal assignment of the casein gene family was confirmed using a mouse albumin clone. The albumin gene had been previously localized to mouse chromosome 5 by both breeding studies and analogous molecular hybridization experiments. An additional control experiment demonstrated that another hormone-inducible gene, specifying a 620 nucleotide abundant mammary gland mRNA, hybridized to DNA isolated from a different somatic cell hybrid line. These studies represent the first localization of a peptide and steroid hormone-responsive gene family to a single mouse chromosome.

J chain is encoded by a single gene unlinked to other immunoglobulin structural genes

Immunoglobulin J chain mediates the polymerization of both IgM and IgA immunoglobulins. Its synthesis is closely regulated in B lymphocytes, apparently at the level of RNA transcription. To define the genetic bases of this regulation, we have determined the location and number of J chain genes in the mouse. Analysis of DNA from a group of somatic cell hybrids containing various mouse chromosomes on a constant background of Chinese hamster chromosomes indicated that this gene is located on mouse chromosome 5, unlinked to immunoglobulin heavy and light chain structural genes. Restriction mapping experiments further suggested the existence of a single J chain gene per haploid genome. This result was confirmed by quantitative analyses of band intensities yielded by Southern blots of mouse genomic DNA and J gene-containing plasmid DNA.

Assignment of the structural gene coding for albumin to human chromosome 4

Albumin is a developmentally regulated serum protein synthesized in the liver mainly during adulthood. Family studies using variant forms of albumin established autosomal linkage between albumin and group-specific component protein (GS). Since GC has been assigned to human chromosome 4, albumin can be indirectly assigned to the same chromosome; however no direct assignment has been made. Recently, the human albumin cDNA probe has been isolated and characterized. It thus permits a direct chromosomal assignment of the albumin gene in the human genome. When the cDNA probe was hybridized to the HindIII digested total human DNA, an intense band at 6.8 kb was present. When the probe was hybridized to the HindIII digested Chinese hamster CHO-K1 DNA, a less intense band at 3.5 kb was found, plus three other faint bands. When the probe was hybridized to a series of human/CHO-K1 cell hybrids retaining a complete hamster genome and various combinations of human chromosomes, it was evident that hybrids containing human albumin gene sequences could be readily distinguished from hybrids containing no human albumin gene. Analysis of 22 primary cell hybrids for the presence or absence of human albumin sequences has assigned the albumin gene to human chromosome 4. Similar results were obtained using another restriction endonuclease EcoR1. Thus, by direct assay of the genomic albumin gene sequences in the cell hybrids, we provide evidence for a direct assignment of the structural gene for human albumin to chromosome 4.