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Biomedical subjects

B G Forget

Publications and source records attributed to B G Forget.

At least 109 records · Page 6Linked to original sources
PubMed1987

Expression of the affected A gamma globin gene associated with Greek nondeletion hereditary persistence of fetal hemoglobin.

The overexpressed A gamma globin gene in the Greek type of nondeletion hereditary persistence of fetal hemoglobin has a unique single-base substitution located at position -117 relative to the site of transcription initiation. This gene and its normal counterpart were transferred into cultured cell lines by using a retroviral vector. The only difference in expression between the transferred normal and mutant gamma genes was observed in the human erythroleukemia cell line KMOE after exposure of the cells to cytosine arabinoside, a condition that resulted in an adult pattern of endogenous globin gene expression by the cells and was associated with increased expression of the mutant gene.

Animals↗
PubMed1987

A new mutation in IVS-1 of the human beta globin gene causing beta thalassemia due to abnormal splicing.

A G to T transversion at the fifth nucleotide of the first intervening sequence (IVS-1) of the beta-globin gene has been identified in cloned beta-thalassemia genes of two unrelated individuals, one of Mediterranean and the other of Anglo Saxon ancestry. In each patient the mutation was present in a different beta globin gene framework, defined by intragenic restriction site polymorphisms, thereby suggesting the occurrence of independent mutations. The study of the RNA products of one of these cloned genes, after transfer and transient expression in HeLa cells, showed partial inactivation of the normal donor splice site of IVS-1 and activation of two major and one minor cryptic splice sites. Only one of the two major cryptic sites was utilized in a cell-free splicing extract. The effects of this mutation on messenger RNA (mRNA) splicing are similar to that of another beta thalassemia gene with a G to C transition at the same position.

Base Sequence↗
PubMed1987

The beta-globin gene on the Chinese delta beta-thalassemia chromosome carries a promoter mutation.

A new type of delta beta-thalassemia characterized by decreased expression of the beta-globin gene and increased expression of both G gamma and A gamma globin gene in the absence of a detectable deletion has recently been described in the Chinese population. In this study we characterize the mutant beta-globin gene from this delta beta-thalassemia chromosome. An A to G transversion is identified in the "ATA" sequence of the promoter region that leads to decreased expression of the beta-globin gene in vivo and in vitro. We also demonstrate the presence of this mutation in every individual with a high fetal hemoglobin phenotype in this family and its absence in every individual with a normal hemoglobin phenotype. This same promoter mutation has recently been detected in Chinese beta-thalassemia genes where it is present on chromosomes of the same haplotype as that of the delta beta-thalassemia chromosome we are studying. These data support the hypothesis that an as yet unidentified mutation occurred on the ancestral chromosome carrying the promoter mutation and subsequently gave rise to the delta beta-thalassemia phenotype.

China↗
PubMed1986

Beta zero thalassemia caused by a base substitution that creates an alternative splice acceptor site in an intron.

A thalassemic beta-globin gene cloned from a haplotype I chromosome contains a T to G transversion at position 116 of IVS1 which results in the generation of an abnormal alternative acceptor splice site. Transient expression studies revealed a 4-fold decrease in the amount of RNA produced with greater than 99% of it being abnormally spliced despite preservation of the normal acceptor splice site at position 130. These results suggest that the mutation at IVS1 position 116 results in beta zero thalassemia. A closely related mutation at position 110 of IVS1 also generates a novel acceptor site and results in a similar decrease in total mRNA produced, but approximately 20% of the mRNA produced is normally spliced and thus the phenotype is that of beta + thalassemia. These observations suggest that short range position effects may play a dramatic role in the choice of potential splice acceptor sites. We demonstrate the presence of abnormally spliced mRNA in reticulocytes of affected individuals and show the mutation at IVS1 position 116 segregating from the mutation at IVS1 position 110 in a three generation pedigree. The mutation results in the creation of a MaeI restriction site, as do a number of other thalassemic mutations, and we demonstrate some difficulties that may arise in the differential diagnosis of these mutations.

Amino Acid Sequence↗
PubMed1986

Cloning of a portion of the chromosomal gene for human erythrocyte alpha-spectrin by using a synthetic gene fragment.

A region of minimal codon degeneracy was selected from the amino acid sequence of the amino-terminal alpha I domain of human erythrocyte spectrin to design a 90-base-pair DNA probe for the screening of a human genomic library. Five complementary oligonucleotides were assembled to form a full-length double-stranded DNA, which was then cloned in an M13 phage vector to generate hybridization probes. Under stringent conditions, a single hybridizing clone was isolated from a total human genomic library. Partial DNA sequence analysis established the 16.8-kilobase-pair isolate as erythrocyte alpha-spectrin by correlation to a known sequence of 131 amino acids. The spectrin 106 amino acid repeat segment is encoded by multiple exons separated by introns of various sizes. Of the 3074 base pairs of DNA sequenced thus far, 12.8% code for amino acids.

Base Sequence↗
PubMed1986

Concordance of a point mutation 5' to the A gamma-globin gene with A gamma beta + hereditary persistence of fetal hemoglobin in Greeks.

In the Greek A gamma beta + type of hereditary persistence of fetal hemoglobin (HPFH), adult heterozygotes produce about 20% fetal hemoglobin (HbF), which is predominantly of the A gamma chain variety. The affected beta-globin gene cluster produces near normal amounts of beta-like globin, but in a A gamma to beta ratio of 20:80 instead of 0.5:99.5. Gelinas et al and Collins et al have shown a G to A change 117 nucleotides 5' to the A gamma gene in two Greeks with A gamma beta + HPFH. To demonstrate that this change is not a neutral polymorphism, we carried out hybridization with oligonucleotide probes (19mers) specific for the normal and the mutant sequences. While normal probe identified the A gamma fragment in genomic DNA of all subjects studied, mutant probe was positive only in Greeks with A gamma beta + HPFH. In sum, 108 beta-globin gene clusters of individuals without HPFH were negative when tested with mutant probe, but all 11 affected individuals of six families with Greek A gamma beta + HPFH (two previously sequenced and four new families) were positive with mutant probe. These data support the conclusion that the -117 mutation is causative of A gamma beta + HPFH in Greeks.

Fetal Hemoglobin↗
PubMed1986

A novel basis for delta beta-thalassemia in a Chinese family.

We have studied a Chinese family in which beta-thalassemia and delta beta-thalassemia were found in simple and compound heterozygous states. The delta beta-thalassemia heterozygote (the mother) had 22.3% hemoglobin F, of which 40% was G gamma and 60% A gamma; globin chain studies showed an alpha/beta + gamma ratio of 1.36. The compound heterozygote for delta beta-thalassemia and beta-thalassemia (the child) had the clinical picture of thalassemia intermedia and an alpha/beta + gamma ratio of 4.44. Gene mapping studies were performed using DNA from the affected child. Seventy kilobases of DNA in the beta-globin gene cluster starting upstream from the epsilon-globin gene and ending downstream from the beta-globin gene were mapped, and no detectable deletions or rearrangements were detected. In addition, heterozygosity was detected at multiple polymorphic restriction sites in and 3' to the beta-globin gene, which excludes the possibility of a deletion of the entire beta-globin gene cluster. This is the first example of a nondeletion delta beta-thalassemia associated with increased expression of both G gamma and A gamma genes.

Female↗
PubMed1986

Identification of a beta-thalassemia mutation associated with a novel haplotype of RFLPs.

The study of the molecular defects that result in beta-thalassemia in Mediterraneans has uncovered a large number of unique mutations. This information is already being utilized for prenatal diagnosis of pregnancies at risk. Here, we report the definitive identification, by molecular cloning, of the beta-thalassemia mutation associated with a Mediterranean chromosome bearing a novel haplotype of restriction fragment length polymorphisms (RFLPs) in the beta gene cluster that has been previously designated as haplotype X. The thalassemia mutation was identified as a T----C base substitution at IVS-1 position 6, a mutation previously described in association with haplotype VI. We describe the use of the restriction enzyme SfaNI for the detection of this mutation and point out a possible pitfall that should be avoided if such an approach is used for the detection of this mutation, which appears to be a common cause of mild beta+-thalassemia in some populations.

Alleles↗
PubMed1985

Beta-thalassemia resulting from a single nucleotide substitution in an acceptor splice site.

Beta-globin gene mutations which alter normal globin RNA splicing have confirmed the necessity of invariant nucleotides GT at donor splice sites. Functional consequences of point mutations in the invariant AG acceptor splice site have not been determined. We have isolated and characterized a beta-globin gene from a Black patient with beta-thalassemia intermedia which has an A-G transition at the usual intervening sequence 2 (IVS2) acceptor splice site. Functional analysis of transcripts produced by this mutant gene in a transient expression vector indicates that the mutation inactivates the normal acceptor splice site and results in some utilization of a cryptic splice site near position 580 of IVS2. This mutation would be expected to produce a beta-globin gene which results in no normal beta-globin mRNA.

Base Sequence↗
PubMed1985

Polyadenylation of a human mitochondrial ribosomal RNA transcript detected by molecular cloning.

We have identified by molecular cloning a polyadenylated RNA transcript in the human leukemia cell line, K562, which is complementary to a portion of the gene-encoding mitochondrial 16S ribosomal RNA (mt 16S rRNA). The cloned portion of the transcript corresponds to positions 2191-2395 of the human mt genome. The clone represents a cDNA copy of an RNA transcript from the H strand and carries an additional poly(A) tail 21 residues long at its 3'-end. Our data provide direct evidence for polyadenylation of some mt 16S rRNA transcripts.

Base Sequence↗
PubMed1984

Beta globin messenger RNA content of bone marrow erythroblasts in heterozygous beta-thalassemia.

RNA from bone marrow erythroblasts and peripheral blood reticulocytes of patients with heterozygous beta-thalassemia was analyzed for relative content of alpha and beta globin messenger RNA by molecular hybrization. Erythroblasts from nonthalassemic patients exhibited approximately the same alpha and beta globin mRNA content (beta/alpha mRNA ratio = 0.8-1.0) as circulating reticulocytes (beta/alpha mRNA ratio = 0.74-1.2). The mRNA ratios corresponded well to levels of globin synthesis observed in bone marrow and peripheral blood. Erythroblasts from four patients with heterozygous beta-thalassemia also exhibited approximately the same beta/alpha mRNA ratios in bone marrow erythroblasts (0.34-0.59) as in reticulocytes (0.34-0.4): beta globin mRNA was clearly deficient in bone marrow erythroblasts. Globin biosynthesis by erythroblasts of beta-thalassemia heterozygotes was balanced despite the mRNA deficiency (beta/alpha = 0.9-1.0), suggesting that post-translational phenoma (eg, proteolysis of free globin chains), rather than instability of beta mRNA, accounts for the balanced globin chain synthesis frequently observed in bone marrow erythroblasts of patients with beta-thalassemia trait.

Adult↗
PubMed1984

G gamma beta+ hereditary persistence of fetal hemoglobin: cosmid cloning and identification of a specific mutation 5' to the G gamma gene.

Hereditary persistence of fetal hemoglobin (HPFH) is a benign condition in which the normal shutoff of fetal hemoglobin (Hb F) production fails to occur. In the G gamma beta+ type of HPFH, erythrocytes of adult heterozygotes contain approximately equal to 20% Hb F, which is almost exclusively of the G gamma-globin variety, without increased levels of gamma-globin chains from the nearby A gamma-globin gene. Unlike some forms of HPFH, no major deletions in the globin gene cluster have been found by genomic blotting in the G gamma beta+ variety. We report here a family with this condition, from which cosmid clones of the beta-globin gene cluster from the G gamma beta+ HPFH allele have been obtained. Sequencing around the fetal genes has identified a point mutation 202 base pairs 5' to the G gamma-globin gene that is present in genomic DNA of 3/3 unrelated individuals with G gamma beta+ HPFH but in none of more than 100 non-HPFH individuals. Although the mutation could represent a tightly linked polymorphism, its location in a region suggested by recent data to be important in tissue-specific control of gene expression suggests the possibility that the -202 mutation accounts for the phenotype. The sequence created resembles elements of other eukaryotic promoters known to be important for efficient transcription.

Base Sequence↗
PubMed1984

Concordance of a point mutation 5' to the G gamma globin gene with G gamma beta +. Hereditary persistence of fetal hemoglobin in the black population.

Hereditary persistence of fetal hemoglobin (HPFH) is a genetically heterogeneous and clinically benign condition characterized by persistent expression of fetal hemoglobin (Hb F) into adulthood. In the G gamma beta + type, no major deletions in the globin gene cluster occur; adult heterozygotes produce approximately 20% Hb F, which results from overproduction of G gamma chains, with no apparent increase in production from the adjacent A gamma gene. We have recently described a point mutation 202 base pairs 5' to the cap site of the G gamma gene in an individual with G gamma beta + HPFH. This mutation abolishes a normal ApaI restriction endonuclease site, and thus can be detected by blotting of genomic DNA. We present here further data on the ApaI mutation: (1) It occurs in six of seven families with G gamma beta + HPFH. (2) In three families, detailed haplotype analysis using 11 polymorphic restriction sites in the beta globin cluster has been done. The two that carry the missing ApaI site are identical but the third, which has a normal ApaI pattern, differs from the other two in at least two sites, one of which is a new polymorphic Nco I site between the delta and beta globin genes. This suggests the possibility of a different HPFH mutation in the third family. (3) The haplotype of the G gamma beta + HPFH chromosome carrying the ApaI mutation is different from that of 108 beta A chromosomes of black individuals that have been tested. (4) The G gamma ApaI site is normal in 61 beta A and 109 beta S alleles from non-HPFH black individuals, including 22 who share the same haplotype for the intragenic G gamma, A gamma HindIII polymorphisms. These data add support to the possibility that the -202 mutation is actually causative of the G gamma beta + HPFH phenotype.

Alleles↗
PubMed1984

Intranuclear defect in beta-globin mRNA accumulation due to a premature translation termination codon.

We have analyzed a cloned beta O-thalassemia (beta O-thal) gene from a patient doubly heterozygous for hemoglobin Lepore and beta O-thalassemia. Studies of 3H-uridine incorporation into beta-globin mRNA in this patient's erythroblasts suggested an intranuclear defect in both beta and Lepore (delta beta) mRNA synthesis, as did S1 nuclease analysis of nuclear RNA. However, the nucleotide sequence of the beta O-thal gene revealed only a single base change in codon 39 (CAG----UAG), which created a premature translation termination codon. The 5' flanking sequence, including transcription promotor boxes and the mRNA initiation (CAP) site, were normal. The unexpected effect of this mutation on intranuclear beta-mRNA synthesis in vivo was studied by insertion of the cloned gene into a plasmid expression vector and transfection into tissue culture (COS-1) cells. beta-Globin mRNA produced by the transfected cells was assessed by S1 nuclease analysis. The beta O-39 thalassemia gene generated five- to tenfold less beta-mRNA than a normal beta-gene in both nuclear and cytoplasmic RNA, simulating the results observed in vivo. Moreover, the small amount of beta O-39 mRNA produced was as stable as normal beta-mRNA during an actinomycin D chase, ruling out rapid cytoplasmic turnover as a cause of the reduced accumulation. Cotransfection of the beta O-39 thalassemia gene with a mutant tyrosine suppressor tRNA gene resulted in restoration of the beta O-39 mRNA accumulation to near-normal levels. On the basis of these results, we suggest that the low levels of beta-mRNA known to exist in the common form of beta O-thalassemia, beta O-39 thalassemia, result from a lesion in transcription, or early posttranscriptional processes; the defect appears to be corrected by restoration of proper translational potential to the mutant mRNA, at least in a gene transfer-expression system in tissue-culture cells.

Base Sequence↗
PubMed1983

Different 3' end points of deletions causing delta beta-thalassemia and hereditary persistence of fetal hemoglobin: implications for the control of gamma-globin gene expression in man.

DNA at the end point of the gene deletion associated with one form of hereditary persistence of fetal hemoglobin (HPFH) was cloned and used as a probe in gene mapping experiments to analyze the extent and approximate 3' end points of various deletions associated with HPFH and delta beta-thalassemia. The deletions in the two known forms of deletion-type HPFH were shown to be considerably more extensive than in the two cases of delta beta-thalassemia studied. The overall extents of the deletions in the two types of HPFH were quite similar in both cases and the 3' end points were located at a minimum distance of approximately equal to 52 and 57 kilobases from the 3' extremity of the beta-globin gene. In contrast, the 3' end points of the deletions in the two forms of delta beta-thalassemia were located approximately equal to 5 and 10 kilobases to the 3' side of the beta-globin gene. The extent of these deletions and the nature of the DNA brought into the vicinity of the gamma-globin genes by the deletions may therefore be a more important influence on the phenotype of the deletions than the specific nature of the DNA sequences that are deleted within the non-alpha-globin gene cluster as a result of the mutations.

Base Sequence↗