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

The ZFHX3 (ATBF1) transcription factor induces PDGFRB, which activates ATM in the cytoplasm to protect cerebellar neurons from oxidative stress

Ataxia telangiectasia (A-T) is a neurodegenerative disease caused by mutations in the large serine-threonine kinase ATM. A-T patients suffer from degeneration of the cerebellum and show abnormal elevation of serum alpha-fetoprotein. Here, we report a novel signaling pathway that links ATM via cAMP-responsive-element-binding protein (CREB) to the transcription factor ZFHX3 (also known as ATBF1), which in turn promotes survival of neurons by inducing expression of platelet-derived growth factor receptor β (PDGFRB). Notably, AG1433, an inhibitor of PDGFRB, suppressed the activation of ATM under oxidative stress, whereas AG1433 did not inhibit the response of ATM to genotoxic stress by X-ray irradiation. Thus, the activity of a membrane-bound tyrosine kinase is required to trigger the activation of ATM in oxidative stress, independent of the response to genotoxic stress. Kainic acid stimulation induced activation of ATM in the cerebral cortex, hippocampus and deep cerebellar nuclei (DCN), predominately in the cytoplasm in the absence of induction of γ-H2AX (a marker of DNA double-strand breaks). The activation of ATM in the cytoplasm might play a role in autophagy in protection of neurons against oxidative stress. It is important to consider DCN of the cerebellum in the etiology of A-T, because these neurons are directly innervated by Purkinje cells, which are progressively lost in A-T.

Role of albumin in human physiology and pathophysiology

Albumin is one of the major products of hepatic protein synthesis. Although it is a small molecule, it is an important diagnostic and prognostic determinant, as well as a useful therapeutic agent. A review of the evolution and structure of albumin as well as a description of its colloidal and buffering properties is presented. Synthesis, distribution, and catabolism, the major determinants of serum albumin level, are discussed. Emphasis is given to those mechanisms responsible for the regulation of these processes, including the importance of nutritional status on substrate availability, energy supply, and hormonal modulation.

Confirmation of assignment of the human alpha 1-crystallin gene (CRYA1) to chromosome 21 with regional localization to q22.3

The crystallins are highly conserved structural proteins universally found in the eye lens of all vertebrate species. In mammals, three immunologically distinct classes are present, alpha-, beta-, and gamma-crystallins, and each class represents a multigene family. The alpha-crystallin gene family consists of alpha 1-crystallin (CRYA1) and alpha 2-crystallin (CRYA2) genes (previously designated alpha A- and alpha B-crystallin, respectively), which show extensive sequence homology. We constructed a synthetic oligonucleotide probe of 25 bases corresponding to a specific region of the human alpha 1-crystallin gene sequence. This 25-mer probe bears little sequence homology to human alpha 2-crystallin gene and does not cross-hybridize to alpha 2-crystallin sequences in Southern blot analysis. Using this unique synthetic probe, we have demonstrated the identity of the alpha 1-crystallin gene in human genomic DNA. In addition, we have also confirmed its chromosomal location on human chromosome 21. Finally, we have regionally localized the gene to q22.3 by using both Southern blot analysis of a panel of cell hybrids containing different parts of human chromosome 21, and in situ hybridization to metaphase chromosomes. The use of synthetic oligonucleotide probes specific for individual genes should be useful in identifying and mapping members of multigene families.

Direct regional assignment of the gene for vitamin D binding protein (Gc-globulin) to human chromosome 4q11-q13 and identification of an associated DNA polymorphism

Using a characterized human vitamin D binding protein (DBP) cDNA probe and a panel of rodent X human somatic cell hybrids, we established the chromosomal location of the structural gene for DBP on human chromosome 4. In situ hybridization of 3H-labeled DBP cDNA to human metaphase chromosomes confirmed this assignment and allowed regional localization to bands 4q11-4q13. A restriction fragment length polymorphism associated with the DBP gene that should prove useful in future linkage studies was identified with the enzyme BamHI.

Molecular genetics of human chromosome 4

The recent discovery that the gene causing Huntington's disease (HD) resides on chromosome 4 has generated increased interest in this autosome. Chromosome 4 contains two of the more informative conventional genetic markers, GC and MNS, but most loci have been assigned to it by recombinant DNA techniques. There are currently more anonymous DNA fragments detecting restriction fragment length polymorphisms (RFLPs) on chromosome 4 than on any other autosome. In addition, most of the cloned genes from this chromosome detect useful RFLPs. A genetic linkage map including both conventional and DNA markers should soon span the entire chromosome and will undoubtedly lead to the localisation of other inherited disorders.

Loss of alleles at polymorphic loci on chromosome 2 in uveal melanoma

The loss of alleles at loci on specific chromosomes in some malignant tumors, such as retinoblastoma and Wilms' tumor, suggests that recessive mutations are important in their oncogenesis. We postulate that similar mechanisms may be involved in the formation of uveal melanomas. We studied alleles at autosomal loci in uveal melanoma cells and in the constitutional cells from 19 patients who developed the tumors. We observed loss of alleles only at loci on chromosome #2. This suggests that recessive alleles at some chromosome #2 locus may be important in the oncogenesis of uveal melanomas.

The gene coding for a sphingolipid activator protein, SAP-1, is on human chromosome 10

SAP-1 is a sphingolipid activator protein found in human tissues required for the enzymatic hydrolysis of GM1 ganglioside and sulfatide. It appears to be missing in patients who have a genetic lipidosis resembling juvenile metachromatic leukodystrophy. Using rabbit antibodies against human SAP-1 it could be visualized in extracts from cultured human skin fibroblasts after sodium dodecylsulfate-polyacrylamide gel electrophoresis, followed by electroblotting to nitrocellulose membrane and immunochemical staining (Western blotting). A series of 23 human-Chinese hamster ovary cell hybrids containing different human chromosomes were examined. The parent Chinese hamster ovary cells did not have a reacting protein in the region of human SAP-1. Only in the eight hybrid clones containing human chromosome 10 was a reacting protein identified. Other chromosomes were excluded by this method. Therefore the gene for SAP-1 and the genetic mutation resulting in a fatal lipidosis are located on human chromosome 10.

Polymorphisms of human albumin gene after DNA restriction by HaeIII endonuclease

Hybridization of albumin clones cDNA with human DNAs digested by several restriction endonucleases reveals two HaeIII polymorphisms. The first polymorphism, H1, is of low frequency (f1 = 0.05); the second, which is validated by family analysis, occurs frequently (f2 = 0.21) and is an intronic polymorphism, probably of substitution--base type.

Genetic mapping of the structural gene for antithrombin III to human chromosome 1

Using a purified cDNA probe of human antithrombin III (AT3) gene and a series of human/Chinese hamster cell hybrids, we established the chromosomal location of the structural gene for AT3 in human chromosome 1 by Southern blot analysis.

DNA restriction fragment length polymorphisms and heterozygosity in the human genome

A list is presented of published reports of DNA polymorphisms found in the human genome by restriction enzyme analysis. While the list indicates the large number of restriction fragment length polymorphisms (RFLPs) detected to date, the information collated is insufficient to permit an estimate of heterozygosity for the genome as a whole. Data from our laboratory are therefore also presented on RFLPs detected using a random sample of cloned DNA segments. Such an analysis has permitted a first unbiassed estimate of heterozygosity for the human genome. Since this figure is an order of magnitude higher than previous estimates derived from protein data, the majority of polymorphic variation present in the human genome must, by implication, occur in noncoding sequences. In addition it was confirmed that enzymes containing the dinucleotide CpG in their recognition sequences detect more polymorphic variation than those that do not contain a CpG. Also presented are the clinical applications of DNA polymorphisms in the diagnosis of human genetic disease.

Localization of the structural gene for human apolipoprotein A-I on the long arm of human chromosome 11

Apolipoprotein A-I (apo A-I), the major apolipoprotein in human high density lipoproteins, is involved in the disease atherosclerosis. Cloned apo A-I cDNA (pA1-3) was used as a probe in chromosome mapping studies to detect the human apo A-I structural gene sequence in human-Chinese hamster cell hybrids. Southern blot analysis of 13 hybrids localized the gene to human chromosome 11. Confirmation of the chromosomal assignment was obtained by analysis of a hybrid (J1) containing a single human chromosome, no. 11. Regional mapping was achieved by using deletion subclones of J1 that localized the human apo A-I structural gene to the region 11q13 leads to qter. Since the human apolipoprotein C-III (apo C-III) structural gene is closely linked to apo A-I, it can be assigned to the same region on the long arm of chromosome 11. By extension of methods previously described, it now appears possible to carry out fine-structure analysis of this and related gene regions on chromosome 11 and to study the biochemical concomitants of these genes and of genes on other chromosomes for analysis of their role in atherosclerosis.

Molecular genetics of human serum albumin: restriction enzyme fragment length polymorphisms and analbuminemia

By using cDNA probes for the human albumin gene, four restriction enzyme fragment length polymorphisms (RFLPs) were discovered that were transmitted by codominant autosomal inheritance. Among Caucasians, the gene frequencies were 0.04/0.96 for Msp I/5', 0.43/0.57 for Hae III/3', 0.44/0.56 for Hae III/5', and 0.04/0.42/0.54 for Pst I/5'. These common variants provide a marker for chromosome 4 (q11-q13). A calculation of the extent of DNA variation at the albumin locus revealed that 1/95 nucleotide sites was affected by a RFLP, a figure similar to that found in the globin system. Restriction enzyme fragment study of the DNA of a human analbuminemic individual revealed no gross structural rearrangements of the albumin locus. The exact nature of abnormality will require more study.