ABSTRACT. Hereditary hemochromatosis mutation 845A (C282Y) in the HFE gene was recently described, and the C282Y frequencies were reported for various world populations. The aim of this study was to determine the Y allele frequencies of the C282Y mutation for five French populations. The most elevated value (= 5.6%) was obtained for Bretons, in accordance to the hypothesis indicating a Celtic origin of the hereditary hemochromatosis mutation.

Keywords: Hereditary hemochromatosis, C282Y mutation, French populations.

Reprint requests to: Professor Gerard Lucotte, Laboratoire de Neurogenetique Moleculaire (Service de Neurologie), Hopital Maison-Blanche, 45 rue Cognacq-Jay, 51092 Reims Cedex France, phone: 33 139727106, fax: 33 139727927

ABSTRACT: Most retroviral vectors used in preclinical and clinical studies contain a selectable marker gene to facilitate the generation of producer clones. However, the expression of such genes in target cells is often undesirable since this may modify cellular phenotype and invoke a host immune response. Unfortunately, the efficient identification of high-titer producer clones for vectors lacking a selectable marker gene continues to be problematic and lacking for a standard methodology. Despite recent improvements in the screening techniques for identifying high-titer producer clones without the aid of a selectable marker, a solution to the fundamental problem of the very low frequency occurrence of high-titer clones within the starting cell population has not emerged. We have developed a strategy which greatly increases the frequency of virus- producing clones, including those with high-titer, within the population of transduced cells to be screened. This approach relies on the use of high-titer vector preparations generated in 293T cells by co-transfection of retroviral packaging and vector plasmids. Viral preparations of a vector lacking a selectable marker were used to repeatedly transduce exponentially growing packaging cells at a high multiplicity of infection (MOI). Each cell in the resulting polyclonal population of producer cells contained multiple copies of the unrearranged vector genome. Greater than 95% of the clones derived from this population produced vector particles as judged by slot blot analysis of viral RNA from conditioned media. Numerous clones with estimated titers of 105-106 were identified. These titers were confirmed using a standard vector genome transmission assay. This approach significantly enhances the ability, without large scale screening, to easily identify high-titer clones lacking a selectable marker and should facilitate the routine use of simplifed gene marking and therapeutic vectors.

Keywords: Retroviral producer cells, selectable marker gene, retroviral vectors.

Reprint requests to: Elio F. Vanin, Ph.D., Division of Experimental Hematology, St. Jude Children's Research Hospital, 332 North Lauderdale Drive, Memphis, TN 38105, phone: (901) 495-2679, fax: (901) 495-2176, e-mail: elio.vanin@stjude.org.

ABSTRACT. The human zeta-globin gene is expressed in a tissue-and developmental-specific pattern, with expression confined to primitive erythroid cells of the embryonic yolk sac blood islands. Transgenic mouse studies have shown that the proximal zeta-globin promoter contains sequences that contribute to the stage- specificity of expression, but no systematic functional studies of the cis elements in the proximal zeta-globin promoter have been reported. In this paper, we show that a number of conserved sequence elements in the zeta-globin promoter are important for promoter activity in transiently transfected K562 erythroleukemia cells, which constitutively express zeta-globin. These include a GATA site at -105, a CCACC site at -93, a CCAAT box at -65, and a TATA box at -29. A highly conserved CCTCC sequence at -78 is not important for zeta-globin promoter activity in this system. Mutations at these sites do not result in increased promoter activity in OCIM1 cells, an erythroid line that does not express zeta-globin, suggesting none of these sites is a developmental silencer. Electrophoretic mobility shift assays show that K562 and OCIM1 nuclear extracts contain DNA-binding activities that interact with the -105 GATA,-65 CCAAT, and -29 TATA sites. In addition K562 cells, but not OCIM1 cells, have an activity that binds the -93 CCACC site. GATA-1 interacts with the GATA site. The K562 CCACC-binding protein is distinct from Sp1, Sp2, Sp3, Sp4, EKLF, and BKLF. A specific -65 CCAAT-binding activity is present in K562 and OCIM1 nuclear extracts that is distinct from other CCAAT-binding proteins including CBF/NF-Y, C/EBP, NF-1, and CP2. Thus, we have identified two novel factors that may contribute to the tissue or developmental stage-specific expression of zeta-globin.

Keywords: Gene expression, transcription factors, embryonic globin, zeta-globin, GATA-1, Sp1, promoters, transfection.

Reprint requests to: Daniel E. Sabath, M.D.,Ph.D., Department of Laboratory Medicine, University of Washington, Box 357110, Seattle, WA 98195-7110, phone: (206) 548-6833, fax: (206) 548-6189, e-mail: dsabath@u.washington.edu.

ABSTRACT. Nramp2 is a gene encoding a transmembrane protein that is important in metal transport, in particular iron. Mutations in nramp2 have been shown to be associated with microcytic anemia in mk/mk mice and defective iron transport in Belgrade rats. Nramp2 contains a classical iron responsive element in the 3' untranslated region that confers iron dependent mRNA stabilization. In this report, we describe a splice variant form of human nramp2 that has the carboxyl terminal 18 amino acids substituted with 25 novel amino acids and has a new 3' untranslated region lacking a classical iron-responsive element. This splice form of nramp2, nramp2 non-IRE, was found to be derived from splicing of an additional exon into the terminal coding exon.

The nramp2 gene is comprised of 17 exons and spans more than 36 kb. It contains an additional 5' exon and intron (exon and intron 1) and an additional 3' exon (exon 17) and intron (intron 16) as compared to nramp1, a homologous gene. The additional exons and introns account for much of the difference in length between nramp2 (>36 kb) and nramp 1 (12 kb). The exon-intron borders of nramp2 exons 3-15 are homologous to nramp1 exons 2-14. The nramp2 5' regulatory region contains two CCAAT boxes but lacks a TATA box. The 5' regulatory region of nramp2 also contains five potential metal response elements (MRE's) that are similar to the MRE's found in the metallothionein-II(A) gene, three potential SP1 binding sites and a single gamma-interferon regulatory element.

Five single nucleotide mutations or polymorphisms were identified within the nramp2 gene. One of these, 1303C A, occurs in the coding region of nramp2 and results in an amino acid change from leucine to isolecine. A polymorphism, 1254T/C, also occurs in the coding region of nramp2 but does not cause an amino acid change. The other 3 polymorphisms are within introns (IVS2+11A/G, IVS4+44C/A, and IVS6+538G/Gdel). In addition, a polymorphic microsatellite TATATCTATATATC (TA)(6-7) (CA)(10-11) CCCCCTATA (TATC)(3)(TCTG)(5) TCCG (TCTA)(6) was identified in intron 3.

Analysis of cDNA derived by direct amplification of reversed transcribed RNA or cDNA clones isolated from a library provide evidence of skipping of exons 10 and 12 of nramp2. Deletion of either of these exons would result in a sequence that remains in frame yet would generate a protein that would lack transmembrane spanning region 7 or 8 respectively. The deletion of a single transmembrane domain would have severe topological consequences.

The coding region of the nramp2 gene of hemochromatosis patients with or without mutations in the hemochromatosis gene, HFE, were examined and found to be normal. One hemochromatosis patient, with a normal HFE genotype, was heterozygous for the 1303C A mutation. Furthermore, in an examination of hemochromatosis patients with mutant HFE and normal HFE genes, we did not observe a linkage disequilibrium of either group with a particular nramp2 haplotype. These data suggest that mutations in nramp2 are not commonly associated with hemochromatosis.

Keywords: Nramp, alternative splicing, iron-responsive element, gene structure, metal response element, hemochromatosis, hypoxia-inducible factor-1.

Reprint requests to: Pauline L. Lee, Ph.D., The Scripps Research Institute, Department of Molecular and Experimental Medicine, 10550 North Torrey Pines Road, La Jolla, CA 92037, phone: (619) 784-8042, fax: (619) 784-2083, e-mail: plee@scripps.edu.