Tetra-/di-nucleotide repeat polymorphism upstream of the human α2-globin gene locus at 16p13.3

A highly polymorphic tetra-/di-nucleotide repeat sequence was identified upstream of the human α2/α1-globin gene pair on chromosome 16p13.3. This microsatellite marker should be useful in α-thalassemia genotype phenotype correlations and in respective population genetics studies.     

Selection at the α-Gpdh locus in experimental populations of Drosophila melanogaster

Three sets of experiments have been conducted in order to evaluate the role of natural selection at the -Gpdh locus in Drosophila melanogaster. (1) The evolution of the F-allele frequency has been followed for many generations in 13 experimental populations having different genetic backgrounds. (2) Egg-to-adult viability has been measured in synthetic populations derived from one locality (Brouilly) and the results have been compared with those of a previous experiment involving a different local population (Tostes). (3) The effects of sodium octanoate on egg-to-adult viability have been measured on the genotypes FF, FS, SF, and SS. The results demonstrate that selection operates on a small block of genes which includes the -Gpdh locus.ERA 406 CNRS: Analyse et mécanismes de maintien du polymorphisme.     

A 191-kb genomic fragment containing the human α-globin locus can rescue α-thalassemic mice

A 191-kb human bacterial artificial chromosome (BAC) containing the human α-globin genomic locus was used to generate transgenic mice that express, exclusively, human α-globin (^huα-globin). Expression of ^huα-globin reaches a level of 36% of that of endogenous mouse α-globin (^muα-globin) on a heterozygous mouse α-thalassemia background (^muα-globin knockout, ^muα^+/−). Hemizygous transgenic mice carrying the ^huα-globin locus on a heterozygous knockout background (^huα^+/0, ^muα^++/−−) demonstrated complementation of most hematologic parameters. By crossing ^huα^+/0, ^muα^++/−− mice, we were able to generate mice entirely dependent on ^huα-globin synthesis. Breeding and fluorescent in situ hybridization studies demonstrate that only mice homozygous for the transgene were able to rescue embryonic lethal homozygous ^muα-globin knockout embryos (^muα^{−−/−−}). Adult rescued mice produce hemoglobin at levels similar to wild-type mice, with partial red cell complementation based on mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red cell distribution width (RDW) measurements. Significant erythrocythemia above wild-type levels seems to be the main compensatory mechanism for the normalization of the hemoglobin levels in the rescued animals. Our studies demonstrate that the ^huα-globin locus in the 191-kb transgene contains all the necessary elements for the regulated expression of ^huα-globin in transgenic mice. This animal model should be valuable for studying the mechanisms regulating ^huα-globin production and for development of therapeutic strategies for β-thalassemia based on downregulation of α-globin expression. We dedicate this article to the memory of our valued friend and colleague Panayiotis A. Ioannou who passed away during the completion of this work     

Heat stability studies at the α-glycerophosphate dehydrogenase locus in populations of Drosophila melanogaster

The level of hidden variation in populations of Drosophila melanogaster at the Gpdh ⁺ locus was determined by thermal stability studies of the protein. The results indicate a lack of variation using these methods both in and between the two common electrophoretic variants. It is suggested that -GPDH is conserved in primary structure, which may be related to its critical role in flight muscle metabolism.This investigation was supported by NIH Research Grants No. GM-11546 and GM-23617. Paper No. 5262 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina 27607.     

Equilibrium frequencies of α-globin genes

A mathematical model has been developed to study the mechanism of the maintenance of variable numbers of α-globin genes in human populations. The model incorporates both selection and unequal crossing-over. The selection is formulated so that a homozygous individual with a double deletion is lethal and a heterozygous individual with a deletion or addition of an α-globin gene in a chromosome has decreased fitness. This differs from the previous models of stabilizing selection studied by Ohta (1981) and Takahata (1981). The effect of random genetic drift on the α-thalassemia polymorphims has also been studied.It has been shown that, although the results obtained are compatible with the observation of the low frequency of triple α-globin loci, it cannot explain the high frequency of single and double deletions in Asian populations. For the latter case, some type of heterozygote advantage may be operating.     

Characterization and strain distribution of four alleles at the hemoglobin α-chain structural locus in the mouse

In a survey of mice from 40 inbred strains, largely previously untested, four alleles were distinguished at the Hba locus, determining structure of adult mouse hemoglobin chain. This finding supports and extends previous sequence studies by others. Methods are given by which each phenotype was characterized by its solubility profile at varying pH and by its chromatography pattern. Concordance was complete between histidine-positive T-4 (defining Hba ^c) and high-intermediate solubility profile. In three inbred strains, a distinct new low-solubility profile, not associated with his-positive T-4, was recognized, and mice with this phenotype were classified as Hba ^d. Implications of observed widely distributed four-allele polymorphism of mouse hemoglobin -chain structure are discussed.This investigation was supported in part by NIH research grant CA-01074 from the National Cancer Institute and in part by the Virginia and D. K. Ludwig Foundation. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care.     

Heterogeneity of the α-globin gene defects in German α-thalassemia affected families

Summary Analysis of -thalassemia syndromes in several German families revealed DNA deletion as well as nondeletion forms as the molecular basis for the defects. Thus, the -thalassemia haplotype was identified as the (–)^3.7 rightward deletion form, and the region of the putative recombination process generating such a deletion was further characterized. In addition three different ° haplotypes, (--)^MED, (--)^>26, and ()^T, could be detected using -and -globin gene-specific probes.     

Proteins binding to the 5''''-flanking regulatory elements of the human β-globin gene~1

The binding of nuclear proteins prepared from mouse erythroid tissue in different developmental stages to the 5'-flanking regulatory elements of human globin gene, two negative control regions(NCR1, -610 to -490 bp; NCR2,-338 to -233bp), was identified. Two stage specific protein factors corresponding to embryonic and fetal stages were found to be capable of binding to NCR2. These data provided evidence that the cis acting elements of the 5'-flanking region might be involved in the developmental control of globin gene and NCR2 might be responsible in part for the silence of globin gene in the embryonic and fetal stages.     

High-resolution FISH mapping of the rat α2u-globulin multigene family

The rat α_2u-globulins are a group of similar proteins that are encoded by a family of approximately 20 genes located a single locus of ≤880 kbp on Chromosome (Chr) 5q. Individual members of this gene family demonstrate complex tissue, hormonal, and developmental expression patterns despite a high degree of sequence similarity among the members and consequently provide an interesting system for studying the evolution of differential gene expression. Hybridization analysis indicated that gene classes, similar to those identified at the homologous MUP locus in the mouse, do not exist within the rat α_2u-globulin locus. Furthermore, cross-hybridization analysis revealed the presence of conserved sequences in the 5′ and 3′ regions flanking the α_2u-globulin genes, some of which were present in an inverted orientation. We have used high-resolution fiber FISH to examine the structural organization of the α_2u-globulin locus, and found the genes to be arranged as an array of both direct and inverted repeats. The organization of the rat α_2u-globulin genes differs from the MUP genes and suggests different evolutionary events have reorganized these homologous sets of genes. Received: 26 July, 1999 / Accepted: 8 December 1999     

Genomic rearrangement of the α-globin gene complex during mammalian evolution

In man, the gene for hydroxyacyl glutathione hydrolase (HAGH; glyoxalase II) is closely linked to the α-globin locus (HBα) on Chromosome 16. HAGH polymorphism in the mouse has now enabled the mapping of the murine homologue. Deletion mapping, congenic strain studies, and characterization of 41 recombinant inbred strains establish that the mouseHagh locus lies very close to the α-globin pseudogene (Hba-ps4) in the vicinity of the major histocompatibility locus (H-2) on chromosome 17. Several other loci have been identified previously that are also closely linked to the human α-globin locus but near the α-globin pseudogeneHba-ps4 in the mouse. These linkage relationships suggest that during the evolution of mice a translocation occurred that subdivided the α-globin locus, leaving one inactive α-globin gene still associated with theHagh locus and linked sequences, while moving and inserting the active α-globin locus and all distal sequences into an internal location on another autosome, the predecessor to mouse chromosome 11.