alpha-Globin genes: thalassemic and structural alterations in a Brazilian population

Seven unrelated patients with hemoglobin (Hb) H disease and 27 individuals with alpha-chain structural alterations were studied to identify the alpha-globin gene mutations present in the population of Southeast Brazil. The -alpha3.7, --MED and -(alpha)20.5 deletions were investigated by PCR, whereas non-deletional alpha-thalassemia (alphaHphalpha, alphaNcoIalpha, aaNcoI, alphaIcalpha and alphaTSaudialpha) was screened with restriction enzymes and by nested PCR. Structural alterations were identified by direct DNA sequencing. Of the seven patients with Hb H disease, all of Italian descent, two had the -(alpha)20.5/-alpha3.7 genotype, one had the --MED/-alpha3.7 genotype, one had the --MED/alphaHphalpha genotype and three showed interaction of the -alpha3.7 deletion with an unusual, unidentified form of non-deletional alpha-thalassemia [-alpha3.7/(aa)T]. Among the 27 patients with structural alterations, 15 (of Italian descent) had Hb Hasharon (alpha47Asp->His) associated with the -alpha3.7 deletion, 4 (of Italian descent) were heterozygous for Hb J-Rovigo (alpha53Ala->Asp), 4 (3 Blacks and 1 Caucasian) were heterozygous for Hb Stanleyville-II (alpha78Asn->Lys) associated with the alpha+-thalassemia, 1 (Black) was heterozygous for Hb G-Pest (alpha74Asp->Asn), 1 (Caucasian) was heterozygous for Hb Kurosaki (alpha7Lys->Glu), 1 (Caucasian) was heterozygous for Hb Westmead (alpha122His->Gln), and 1 (Caucasian) was the carrier of a novel silent variant (Hb Campinas, alpha26Ala->Val). Most of the mutations found reflected the Mediterranean and African origins of the population. Hbs G-Pest and Kurosaki, very rare, and Hb Westmead, common in southern China, were initially described in individuals of ethnic origin differing from those of the carriers reported in the present study and are the first cases to be reported in the Brazilian population.

Screening for mutations in human alpha-globin genes by nonradioactive single-strand conformation polymorphism

Point mutations and small insertions or deletions in the human alpha-globin genes may produce alpha-chain structural variants and alpha-thalassemia. Mutations can be detected either by direct DNA sequencing or by screening methods, which select the mutated exon for sequencing. Although small (about 1 kb, 3 exons and 2 introns), the alpha-globin genes are duplicate (alpha2 and alpha1) and highy G-C rich, which makes them difficult to denature, reducing sequencing efficiency and causing frequent artifacts. We modified some conditions for PCR and electrophoresis in order to detect mutations in these genes employing nonradioactive single-strand conformation polymorphism (SSCP). Primers previously described by other authors for radioactive SSCP and phast-SSCP plus denaturing gradient gel electrophoresis were here combined and the resultant fragments (6 new besides 6 original per alpha-gene) submitted to silver staining SSCP. Nine structural and one thalassemic mutations were tested, under different conditions including two electrophoretic apparatus (PhastSystem™ and GenePhor™, Amersham Biosciences), different polyacrylamide gel concentrations, run temperatures and denaturing agents, and entire and restriction enzyme cut fragments. One hundred percent of sensitivity was achieved with four of the new fragments formed, using the PhastSystem™ and 20% gels at 15ºC, without the need of restriction enzymes. This nonradioactive PCR-SSCP approach showed to be simple, rapid and sensitive, reducing the costs involved in frequent sequencing repetitions and increasing the reliability of the results. It can be especially useful for laboratories which do not have an automated sequencer.

Primary structure and evolutionary relationship between the adult alpha-globin genes and their 5'-flanking regions of Xenopus laevis and Xenopus tropicalis

To investigate the evolution of globin genes in the genus Xenopus, we have determined the primary structure of the related adult alpha I- and alpha II-globin genes of X. laevis and of the adult alpha-globin gene of X. tropicalis, including their 5'-flanking regions. All three genes are comprised of three exons and two introns at homologous positions. The exons are highly conserved and code for 141 amino acids. By contrast, the corresponding introns vary in length and show considerable divergence. Comparison of 900 bp of the 5'-flanking region revealed that the X. tropicalis gene contains a conserved proximal 310-bp promoter sequence, comprised of the canonical TATA and CCAAT motifs at homologous positions, and five conserved elements in the same order and at similar positions as previously shown for the corresponding genes of X. laevis. We therefore conclude that these conserved upstream elements may represent regulatory sequences for cell-specific regulation of the adult Xenopus globin genes.

Transcriptional activation of human adult alpha-globin genes by hypersensitive site-40 enhancer: function of nuclear factor-binding motifs occupied in erythroid cells.

The developmental stage- and erythroid lineage-specific activation of the human embryonic zeta- and fetal/adult alpha-globin genes is controlled by an upstream regulatory element [hypersensitive site (HS)-40] with locus control region properties, a process mediated by multiple nuclear factor-DNA complexes. In vitro DNase I protection experiments of the two G+C-rich, adult alpha-globin promoters have revealed a number of binding sites for nuclear factors that are common to HeLa and K-562 extracts. However, genomic footprinting analysis has demonstrated that only a subset of these sites, clustered between -130 and +1, is occupied in an erythroid tissue-specific manner. The function of these in vivo-occupied motifs of the alpha-globin promoters, as well as those previously mapped in the HS-40 region, is assayed by site-directed mutagenesis and transient expression in embryonic/fetal erythroid K-562 cells. These studies, together with our expression data on the human embryonic zeta-globin promoter, provide a comprehensive view of the functional roles of individual nuclear factor-DNA complexes in the final stages of transcriptional activation of the human alpha-like globin promoters by the HS-40 element.

Conserved sequences and cell-specific DNase I hypersensitive sites upstream from the co-ordinately expressed alpha I- and alpha II-globin genes of Xenopus laevis

The globin gene family of Xenopus laevis comprises pairs of closely related genes that are arranged in two clusters, each pair of genes being co-ordinately and stage-specifically expressed. To get information on putative regulatory elements, we compared the DNA sequences and the chromatin conformation 5' to the co-ordinately expressed adult alpha-globin genes. Sequence analysis revealed a relatively conserved region from the cap site up to position -289, and further upstream seven distinct boxes of homology, separated by more diverged sequences or deletions/insertions. The homology boxes comprise 22 to 194 base-pairs showing 78 to 95% homology. Analysis of chromatin conformation showed that DNase I preferentially cuts the upstream region of both genes at similar positions, 5' to the T-A-T-A and the C-C-A-A-T boxes, only in chromatin of adult erythroblasts and erythrocytes, where adult globin genes are expressed, but not in chromatin of adult liver cells or larval erythrocytes, where these genes are silent. This suggests that cell- and stage-specific activation of these genes coincides with specific changes in chromatin conformation within the proximal upstream region. No difference was found in the nucleotide sequence within the DNase I hypersensitive region proximal to the adult alpha 1-globin gene in DNA from embryonic cells, in which this gene is inactive, and adult erythrocytes, expressing this gene.

Promoter region sequence differences in the A and G gamma globin genes of Brazilian sickle cell anemia patients

Fetal hemoglobin (HbF), encoded by the HBG2 and HBG1 genes, is the best-known genetic modulator of sickle cell anemia, varying dramatically in concentration in the blood of these patients. This variation is partially associated with polymorphisms located in the promoter region of the HBG2 and HBG1 genes. In order to explore known and unknown polymorphisms in these genes, the sequences of their promoter regions were screened in sickle cell anemia patients and correlated with both their HbF levels and their βS-globin haplotypes. Additionally, the sequences were compared with genes from 2 healthy groups, a reference one (N = 104) and an Afro-descendant one (N = 98), to identify polymorphisms linked to the ethnic background.The reference group was composed by healthy individuals from the general population. Four polymorphisms were identified in the promoter region of HBG2 and 8 in the promoter region of HBG1 among the studied groups. Four novel single nucleotide polymorphisms (SNP) located at positions -324, -317, -309 and -307 were identified in the reference group. A deletion located between -396 and -391 in the HBG2 promoter region and the SNP -271 C→T in the HBG1 promoter region were associated with the Central African Republic βS-globin haplotype. In contrast, the -369 C→G and 309 A→G SNPs in the HBG2 promoter region were correlated to the Benin haplotype. The polymorphisms -396_-391 del HBG2, -369 SNP HBG2 and -271 SNP HBG1 correlated with HbF levels. Hence, we suggest an important role of HBG2 and HBG1 gene polymorphisms on the HbF synthesis.

Changes in gene expression in PBMCs profiles of PPAR alpha target genes in obese and non-obese individuals during fasting

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Reduction of two functional gamma-globin genes to one: an evolutionary trend in New World monkeys (infraorder Platyrrhini).

Nucleotide sequences were determined for the gamma1- and gamma2-globin loci from representatives of the seven anciently separated clades in the three extant platyrrhine families (Atelidae, Pitheciidae, and Cebidae). These sequences revealed an evolutionary trend in New World monkeys either to inactivate the gamma1 gene or to fuse it with the gamma2 gene, i.e. to have only one functional fetally expressed gamma gene. This trend is clearly evident in six of the seven clades: (i) it occurred in atelids by deletion of most of the gamma1 gene in the basal ancestor of this clade; (ii-iv) in pitheciid titi, saki, and cebid capuchin monkeys by potentially debilitating nucleotide substitutions in the proximal CCAAT box of the gamma1 promoters and (v and vi) in cebid owl and squirrel monkeys by crossovers that fused 5' sequence from gamma1 with 3' sequence from gamma2. In the five clades with gamma1 and gamma2 loci separated by intergenic sequences (the fifth clade being the cebid marmosets), the gamma2 genes retained an unaltered proximal CCAAT motif and their gamma2 promoters accumulated fewer nucleotide substitutions than did the gamma1 promoters. Thus, phylogenetic considerations indicate that the stem platyrrhines, ancestral to all New World monkeys, had gamma2 as the primary fetally expressed gamma gene. A further inference is that when the earlier stem anthropoid gamma gene duplicated, gamma2 (at its greater downstream distance from epsilon) could evade embryonic activation by the locus control region but could be fetally activated once released by regulatory mutations from fetal repressors.

Mouse model of human beta zero thalassemia: targeted deletion of the mouse beta maj- and beta min-globin genes in embryonic stem cells.

beta zero-Thalassemia is an inherited disorder characterized by the absence of beta-globin polypeptides derived from the affected allele. The molecular basis for this deficiency is a mutation of the adult beta-globin structural gene or cis regulatory elements that control beta-globin gene expression. A mouse model of this disease would enable the testing of therapeutic regimens designed to correct the defect. Here we report a 16-kb deletion that includes both adult beta-like globin genes, beta maj and beta min, in mouse embryonic stem cells. Heterozygous animals derived from the targeted cells are severely anemic with dramatically reduced hemoglobin levels, abnormal red cell morphology, splenomegaly, and markedly increased reticulocyte counts. Homozygous animals die in utero; however, heterozygous mice are fertile and transmit the deleted allele to progeny. The anemic phenotype is completely rescued in progeny derived from mating beta zero-thalassemic animals with transgenic mice expressing high levels of human hemoglobin A. The beta zero-thalassemic mice can be used to test genetic therapies for beta zero-thalassemia and can be bred with transgenic mice expressing high levels of human hemoglobin HbS to produce an improved mouse model of sickle cell disease.

Sp1 functions in a chromatin-dependent manner to augment human alpha-globin promoter activity.

The 5' flanking region of the human alpha-globin gene is highly G + C rich and contains multiple copies of the consensus sequence for the Sp1 binding site. We investigated the role of this G + C-rich region in augmenting alpha-globin promoter activity in the presence of the far-upstream alpha-globin enhancer, HS-40. We show that in transiently transfected erythroid cells, deletion of the alpha-globin G + C-rich 5' flanking region has no effect on alpha-globin promoter activity. However, upon stable integration into chromatin, deletion of this region causes a nearly 90% decrease in promoter activity compared with expression from an alpha-globin promoter retaining this region. These results suggest that the alpha-globin G + C-rich 5' flanking region augments alpha-globin promoter activity in a chromatin-dependent manner. We further show that this G + C-rich region is required for the activation of alpha-globin gene expression during erythroid differentiation. Finally, we show by both footprint analysis and functional assays that the ability of the G + C-rich region to increase alpha-globin promoter activity from a stably integrated alpha-globin gene is mediated by its multiple binding sites for the transcription factor Sp1.

Analysis of Alpha CA Genes in Early Vertebrates and ; High-Invertebrates

Carbonic anhydrases are enzymes that are ubiquitously found in all organisms that are engaged in catalyzing the hydration of carbon dioxide to form bicarbonate and proton and vice versa. They are crucial in the process of respiration, bone resorption, pH regulation, ion transport, and photosynthesis in plants. Out of the five classes of carbonic anhydrase α, β, γ, δ, ζ this study focused in the α carbonic anhydrases. This class of CAs constitute of 16 subfamilies in mammals that include 3 non-active enzymes known as Carbonic Anhydrase Related Proteins. The inactiveness of these enzymes is due to the loss of one or more Histidine residues in the active site. This thesis was conducted based on the aim of studying evolutionary analysis of carbonic anhydrase sequences from organisms spanning from the Cambrian age. It was carried out in two phases. The first phase was the sequence collection, which involved many biological sequence databases as a source. The scope of this segment included sequence alignments and analysis of the sequence manually and in an automated form incorporating few analysis tools. The second Phase was phylogenetic analysis and exploring the subcellular location of the proteins, which was key for the evolutionary analysis. Through the medium of the methods conducted with respect to the phases mentioned above, it was possible to accomplish the desired result. Certain thought-provoking sequences were come across and analyzed thoroughly. Whereas, Phylogenetics showed interesting results to bolster previous findings and new findings as well which lay bedrock for future intensified studies.

Thalassemia intermedia as a result of heterozygosis for ß0-thalassemia and aaaanti-3.7/aa genotype in a Brazilian patient

We report a case in which the interaction of heterozygosis for both the ß0-IVS-II-1 (G->A) mutation and the aaaanti-3.7 allele was the probable cause for the clinical occurrence of thalassemia intermedia. The propositus, a 6-year-old Caucasian Brazilian boy of Portuguese descent, showed a moderately severe chronic anemia in spite of having the ß-thalassemia trait. Investigation of the alpha-globin gene status revealed heterozygosis for alpha-gene triplication (aaa/aa). The patient's father, also presenting mild microcytic and hypochromic anemia, had the same alpha and ß genotypes as his son, while the mother, not related to the father and hematologically normal, was also a carrier of the aaaanti-3.7 allele. The present case emphasizes the need for considering the possibility of alpha-gene triplication in ß-thalassemia heterozygotes who display an unexpected severe phenotype. The ß-thalassemia mutation found here is being described for the first time in Brazil.

Influence of the polymorphisms of the α-major regulatory element HS-40 on in vitro gene expression

The α-MRE is the major regulatory element responsible for the expression of human α-like globin genes. It is genetically polymorphic, and six different haplotypes, named A to F, have been identified in some population groups from Europe, Africa and Asia and in native Indians from two Brazilian Indian tribes. Most of the mutations that constitute the α-MRE haplotypes are located in flanking sequences of binding sites for nuclear factors. To our knowledge, there are no experimental studies evaluating whether such variability may influence the α-MRE enhancer activity. We analyzed and compared the expression of luciferase of nine constructs containing different α-MRE elements as enhancers. Genomic DNA samples from controls with A (wild-type α-MRE) and B haplotypes were used to generate C-F haplotypes by site-directed mutagenesis. In addition, three other elements containing only the G→A polymorphism at positions +130, +199, and +209, separately, were also tested. The different α-MRE elements were amplified and cloned into a plasmid containing the luciferase reporter gene and the SV40 promoter and used to transiently transfect K562 cells. A noticeable reduction in luciferase expression was observed with all constructs compared with the A haplotype. The greatest reductions occurred with the F haplotype (+96, C→A) and the isolated polymorphism +209, both located near the SP1 protein-binding sites believed not to be active in vivo. These are the first analyses of α-MRE polymorphisms on gene expression and demonstrate that these single nucleotide polymorphisms, although outside the binding sites for nuclear factors, are able to influence in vitro gene expression.

Genes encoding tumor necrosis factor alpha and granzyme A are expressed during development of autoimmune diabetes.

Progressive destruction of the insulin-producing beta cells in nonobese diabetic mice is observed after infiltration of the pancreas with lymphocytes [Makino, S., Kunimoto, K., Muraoka, Y., Mizushima, Y., Katagiri, K. & Tochino, Y. (1980) Exp. Anim. (Tokyo) 29, 1-13]. We show that the genes for tumor necrosis factor alpha and granzyme A, a serine protease associated with cytoplasmic granules of cytotoxic cells, are expressed during the development of spontaneous diabetes mellitus in the nonobese diabetic mouse. Granzyme A-positive cells are found both in and surrounding the islets, implying induction prior to islet infiltration. Tumor necrosis factor alpha expression is exclusively observed in the intra-islet infiltrate, predominantly in lymphocytes adjacent to insulin-producing beta cells, the targets of the autoimmune destruction, implying that tumor necrosis factor alpha expression is induced locally--i.e., in the islet. A considerable portion of cells expressing tumor necrosis factor alpha appear to be CD4+ T cells. This T-cell subset was previously shown to be necessary for development of the disease. Thus, these findings may be important for understanding the pathogenesis of autoimmune diabetes mellitus and potentially also for that of other T-cell-mediated autoimmune diseases.